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- ! klogical Repal 85(7.25): ;‘*’ <

September 1989

THE ECOLOGY OF THE

SEAGRASS MEADOWS

OF THE WEST COAST

OF FLORIDA:

A

Community

Profile

a

Minerals Management Serviceand

Fish and Wildlife ServiceU.S. Department of the Interior

Biological Report 85(7.25)September 1989

THE ECOLOGY OF THE SEAGRASS MEADOWS OF THE WESTCOAST OF FLORIDA: A COMMUNITY PROFILE

Joseph C. ZiemanRita T. Zieman

Department of Environmental SciencesUniversity of Virginia

Charlottesville, VA 22903

Project OfficerEdward Pendleton

U.S. Fish and Wildlife ServiceNational Wetlands Research Center

1010 Gause BoulevardSlidell, LA 70458

Conducted in Cooperation WithMinerals Management Service

Gulf of Mexico

U.S. Department of the InteriorFish and Wildlife ServiceResearch and DevelopmentWashington, D C 20240

DISCLAIMER

T h e o p i n i o n s a n d r e c o m m e n d a t i o n s e x p r e s s e d i n t h i s r e p o r t a r e t h o s e o f t h e a u t h o r sa n d d o n o t n e c e s s a r i l y r e f l e c t t h e v i e w s o f t h e U . S . F i s h a n d W i l d l i f e S e r v i c e , n o rdoes the mention of trade names constitute endorsement or recommendations for use bythe Federal Government.

Library of Congress Cataloging-in-Publication Data

Zieman, Joseph C.The ecology of the seagrass meadows of the west coast of Florida.

(Biological report ; 85 (7.25)“National Wetlands Research Center.”“Conducted in cooperation with Minerals Management Service, Gulf of Mexico.”“September 1989.”Bibliography: p.1. Marine ecology--Florida. 2. Marine ecology--Mexico, Gulf of. 3.

Seagrasses--Florida--Ecology. 4. Seagrasses--Mexico, Gulf of--Ecology. I.Zieman, Rita T. II. Pendleton, Edward C. III. National Wetlands Research Center(U.S.) IV. United States. Minerals Management Service. V. Title. VI. Series:Biological report (Washington, D.C.) ; 857.25.

QH105.F6Z49 1989 574.5’2636’0916364 89-600197

S u g g e s t e d c i t a t i o n :

Z i e m a n , J . C . , and R.T . Z ieman. 1989. The ecology of the seagrass meadows of the westcoast of Florida: a community profile. U.S. Fish Wildl. Serv. Biol. Rep.85(7.25). 155 pp.

PREFACE

Seagrass beds have come to be known asextremely productive and valuable coastalwetland resources. They are criticalnursery areas for a number of fish,shrimp, and crab species, and support theadults of these and other species thatforage around seagrass beds, preying onthe rich and varied fauna that occur inthese habitats. Seagrass beds supportseveral endangered and threatenedspecies, including sea turtles andmanatees along the west coast of Florida,the geographic area covered in thisprofile.

For these reasons and others, seagrassbeds or meadows have been the topic ofseveral of the reports in this communityprofile series. This report, coveringthe seagrass community of the FloridaGulf of Mexico coastline from south ofTampa Bay to Pensacola, is the fifthcommunity profile to deal with submergedaquatic vegetation beds; others in theseries have synthesized ecologic data onseagrasses of south Florida, eelgrassbeds in the Pacific Northwest and alongthe Atlantic coast, and kelp forests ofthe central California coastline.

These reports in total represent amajor effort toward summarizing and

synthesizing what is known of theecologic structure, functioning, andvalues of these marine and estuarinecommunities. This profile in particularbuilds on the author's earlier profile onthe seagrass meadows of south Florida.As will become apparent to the reader,while enough is known to describe thegulf coast seagrass community, there hasbeen little study of the finer points ofthe structure and function of seagrassbeds in this region. To shed light onthe ecology of Thalassia, Syringodium,and Halodule meadows on Florida's aulf.,coast, one is forced to extrapolate agood deal from information from studiesconducted on the south and southeastFlorida coasts and elsewhere. However,in so doing the author has been able toupdate his own earlier communitv profile.Thus, The Ecology of the Seagra;s'Meadows- -of the West Coast of Florida is not only- -a synthexof &IC, but also servesas- a state-of-the-art review ofsubtropical seagrass ecology and a

this series, the profile finally high-lights how much is still left to learnabout these valuable natural habitats.

iii

CONVERSION FACTORS

Multiplymillimeters (mm)centimeters (cm)meters (m)meters (m)kilometers (km)kilometers (km)

BY To Obtain0.03937 inches0.3937 inches3.281 feet0.5468 fathoms0.6214 statute miles0.5396 nautical miles

square meters (m’) 10.76square kilometers (km’) 0.3861hectares (ha) 2.471

liters (I)cubic meters (m3)cubic meters (m3)

0.2642 gallons35.31 cubic feet

0.0008110 acre-feet

milligrams (mg)grams (9)kilograms (kg)metric tons (1)metric tons (1)

0.00003527 ounces0.03527 ounces2.205 pounds

2205.0 pounds1.102 short tons

kilocalories (kcal)Celsius degrees (‘C)

3.968 British thermal units1.8(%) + 32 Fahrenheit degrees

inches 25.40inches 2.54feet (ft) 0.3048fathoms 1.829statute miles (mi) 1.609nautical miles (nmi) i ,852

square feet (ft2)square miles (mi2)acres

gallons (gal)cubic feet (ft3)acre-feet

ounces (02)ounces (02)pounds (lb)pounds (lb)short tons (ton)

British thermal units (Etu) 0.2520

Metric to U.S. Customary

U.S. Customary to Metric

0.0929 square meters2.590 square kilometers0.4047 hectares

3.785 liters0.02831 cubic meters

1233.0 cubic meters

28350.0 milligrams28.35 grams

0.4536 kilograms0.00045 metric tons0.9072 metric tons

kilocaloriesCelsius degreesFahrenheit degrees (“F) 0.5556 (“F - 32)

square feetsquare mrlesacres

millimeterscentimetersmetersmeterskilometerskilometers

iv

CONTENTS

PREFACE ...........................................................................CONVERSION FACTORS ................................................................FIGURES ...........................................................................TABLES ............................................................................ACKNOWLEDGMENTS ...................................................................

CHAPTER 1. INTRODUCTION ..........................................................

:*:Seagrass Ecosystems .....................................................

1:3The Seagrasses of the West Coast of Florida .............................Physical Environment ....................................................

:::Geologic Environment ....................................................Succession and Ecosystem Development ....................................

CHAPTER 2 AUTECOLOGY OF FLORIDA GULF COAST SEAGRASSES ...........................

2.1 Plant Morphology and Growth .............................................

zReproduction ............................................................

214Plant Constituents ......................................................Physiological Ecology ...................................................2.4.1 Environmental Tolerances and Responses ...........................2.4.2 Photosynthetic Carbon Fixation ...................................2.4.3 Isotopic Fractionation ...........................................

2.5 Nutrient Uptake and Supply ..............................................

CHAPTER 3 DISTRIBUTION, BIOMASS, AND PRODUCTIVITY ...............................

3.1 Distribution ... ........................................................3.1.1 Seagrass Distribution in Tampa Bay ...............................3.1.2 Seagrass Distribution in the Big Bend Area .......................

3.2 Biomass .................................................................3.2.1 Seagrass Biomass in Tampa Bay ....................................3.2.2 Seagrass Biomass in the Big Bend Area ............................

3.3 Productivity ............................................................3.3.1 Seagrass Productivity in Tampa Bay ...............................3.3.2 Seagrass Productivity in the Big Bend Area .......................

CHAPTER 4. COMPONENTS OF THE SEAGRASS COMMUNITY ..................................

4.1 Algal Associates ........................................................4.1.1 Phytoplankton ....................................................4.1.2 Benthic Algae ....................................................4.1.3 Epiphytic Algae ..................................................

4.2 Invertebrates ...........................................................4.3 Fishes ..................................................................

V

Page

iiiiv

viiviii

ix

1

11

:2'14

;:232324

27

27272934

::37

:;

40

t;

t:4648

Page

4.4 Reptiles ................................................................4.5 Birds ...................................................................4.6 Mammals .................................................................

CHAPTER 5. STRUCTURAL AND FUNCTIONAL RELATIONSHIPS IN SEAGRASS SYSTEMS...........

5.1

5.2

5.3

CHAPTER 6

6.16.26.36.46.5

The Relationship of Structure, Shelter, and Predation ...................5.1.1 Fauna1 Abundance and Structure ...................................5.1.2 Structure and Predation ..........................................5.1.3 Fauna1 Sampling: The Problems of Gear and Technique ..............General Trophic Structure ...............................................5.2.1 Seagrass Grazers .................................................5.2.2 Epiphyte Seagrass Complex ........................................5.2.3 Detrital Feeding .................................................5.2.4 Carnivory........................................................5.2.5 Trophies and Ontogenetic Development

of Grassbed Fishes ...............................................Decomposition and Detrital Processing ...................................

INTERFACES WITH OTHER SYSTEMS .........................................

Salt Marsh and Mangrove .................................................Gulf Reefs ..............................................................Continental Shelf .......................................................Export of Seagrass ......................................................Nursery Grounds .........................................................6.5.1 Blue Crabs .......................................................6.5.2 Shrimp ...........................................................6.5.3 Fish...............................~ .............................6.5.4 Detached Macrophytes as Nursery Habitat ..........................

CHAPTER 7. HUMAN IMPACTS AND APPLIED ECOLOGY .....................................

7.1 Dredging, Filling, and Other Physical Damage ............................7.1.1 Acute Stress .....................................................7.1.2 Other Physical Damage ............................................7.1.3 Chronic Effects ..................................................

7.2 Eutrophication and Sewage ...............................................7.3 Oil .....................................................................7.4 Temperature and Salinity ................................................7.5 Paper Mill Effluents ....................................................7.6 Disturbance, Recolonization, and Restoration ............................

7.6.17.6.27.6.3

7.7 Final

REFERENCES.....APPENDIX: FISH

Disturbance ......................................................Recolonization ...................................................Restoration ......................................................

Thoughts ..........................................................

SpECIEj.;;kVEVs.IN.SbUjH'ANb'WESiikN'iib~~~~::::::::::::::::::::::

535354

58

585860666768707071

7272

77

777981838484858686

88

888890919191939595959699

101

103131

vi

Number

FIGURES

Page

17

181920

2122

2324

Z

2728

Location Map of Florida ...................................................... 1The seagrasses of the west Florida coast ..................................... 4Temperatures at four locations in coastal Florida ........................... 5Coastal geology of the Florida west coast .................................... 8General morphology of a Thalassia plant ...................................... 12Flowers of Thalassia and Syringodium (Durako) ................................ 13Temperature responses of Thalassia and Syringodiumon the west Florida coast .................................................... 19Carbon isotopic variation at two locations in Florida ........................ 24Seagrass coverage in Tampa Bay, 1879 and 1982 ................................ 28Seagrass meadow types in Tampa Bay ........................................... 29Seagrass distribution and density in Big Bend area ........................... 30Seagrass species distribution in the Big Bend area ........................... 31Depth distribution of seagrass biomass in Apalachee Bay ...................... 32Seasonal cycle of Thalassia at two stations in Apalachee Bay ................. 37Location of recently fixed carbon photosynthate in Thalassia ................. 38Seasonal changes in productivity of seagrasses and redalgae in Apalachee Bay ....................................................... 39Distribution and diversity of benthic marine plants in theGulf of Mexico ............................................................... 42Representative temperate (Carolinean) invertebrate communities ............... 47Representative tropical (West Indian) invertebrate communities ............... 48Comparison of fauna1 abundance between seagrass beds andadjacent habitats ............................................................ 58Salt-marsh zonation in Florida ............................................... 79Life histories of spotted sea trout and snook on the westFlorida coast ................................................................ 80Fauna1 zonation of west Florida shelf ........................................ 82Eastern Gulf of Mexico current patterns during summer ........................ 83Blue crab spawning migrations and larval transport ........................... 85Channel through grassbed with open-water dredge disposal areain Tampa Bay ................................................................. 89Dredged and filled areas in Boca Ciega Bay ................................... 90Crystal River power plant .................................................... 93

vii

TABLES

Number

1234

z789

1':1213141516171819

Page

Precipitation statistics for gulf coast stations .............................Sediment characteristics of the west coast of Florida ........................Constituents of seagrasses

!...................................................

Seasonal changes in protein and carbohydrates in seagrasses in Tampa Bay15

..... 18Representative values of seagrass biomassBiomass partitioning in seagrasses

.................................... 35...........................................

Seagrass biomass in Tampa Bay area36

........................................... 36Representative values of seagrass productivity ...............................Macroalgae of seagrass communities of west Florida

37

Algal epiphytes of the seagrasses of Florida........................... 43

..............................Fishes of Apalachee Bay...................................................:::Seagrass-associated fish families

:;..............................

Seagrass and wetlands associated birds of the Florida west coast:::::::::::::Comparative abundance of organisms in seagrass and sand habitats

z:.............

Influence of seagrass community structure on fauna1 abundance59

................Wetlands acreage on the west Florida coast

61.......................... 77

Historic human impact on Florida seagrass meadows...................:::::::: 1 97Seagrass damage and restoration assessmentSuccess of seagrass restoration techniques

................................... 99

................................... 100

. . .VIII

ACKNOWLEDGMENTS

The production of this manuscript turnedinto a much larger project than wasenvisioned when we began. During that time,many people contributed greatly towards theproduction of the final product. Theauthors are especially grateful to RichardL. Iverson who contributed both writtenmaterial and numerous published andunpublished figures for Chapters 2 and 3.

We wish to give special thanks to ourproject officer, Edward C. Pendleton, whohas been unusually conscientious throughoutall aspects of the project, starting withthe outline and continuing to the final

production. We especially thank him for hispatience in the face of numerousunanticipated delays.

Critical comments and reviews were madeby Ron Phillips, Robin Lewis, Mike Durako,Laura Gabanski, Cheryl Vaughn, Charles Hill,Robert Rogers, David Moran, Ed Pendleton,and Lorna Sicarello. Robin Lewis and MikeDurako also thoughtfully provided severalillustrative photographs.

Sue Lauritzen did the layout and DaisySingleton and Joyce Rodberg keyboarded thefinal draft.

ix

NWRC

This page has been left blank intentionally.

CHAPTER 1. INTRODUCTION

1 .l SEAGRASS ECOSYSTEMS

Seagrass meadows are recognized today asone of the most important communities inshallow coastal waters. Rapidly growingseagrass leaves serve as the basis of aproductive grazing and detrital food web,while the canopy structure formed by theseleaves offers shelter and protection frompredation for innumerable small organisms,many of which are the juveniles ofimportant commercial species. The coastalwaters of Florida are especially rich inseagrass resources. The two largestseagrass meadows in Florida have receivedlittle human disturbance thus far. Thelargest, in Florida Bay, is approximately5,500 km2, and is protected fromlarge-scale human impact because it ismostly within the boundaries of EvergladesNational Park. The second largest bed isjust off the northwest coast of Florida,between Tarpon Springs and St. Marks, andis approximately 3,000 km2 (Iverson andBittaker 1986). Other seagrass meadows,especially those within urbanizedestuaries, have not fared as well. Lewiset al. (1985a) found that in 1982, TampaBay contained 5,750 ha of seagrass cover.From old maps and aerial photographs theyestimated the historical coverage to benearly 31,000 ha, thus showing a reductionto less than 20% of the historicalcoverage.

The coastline of western Florida is amajor ecocline for the tropical seagrassspecies. Although the distance is notgreat, about 650 km from Florida Bay toApalachicola Bay, it represents a shiftfrom a region in the south where tropicalseagrasses reach their highestdevelopment, to areas that are thenorthern limits of distribution forseveral of the species, notably Thalassiaand Syringodium. While this report

addresses the west and northwest coast ofFlorida, the area of central interest forthis community profile is the region fromTampa Bay to Apalachicola Bay (Figure 1).This region contains the large offshorebeds of the Big Bend area, as well asseveral representative estuarine systems.It is largely defined by the availabledata base for the Florida west coast.

Compared with seagrass meadows insouthern Florida, communities of westernFlorida and the northeastern Gulf ofMexico have received little attention fromthe research community; therefore, thiscommunity profile will refer to data fromsouth Florida and the Caribbean when

ApalachicoloBQY

G U L F O FM E X I C O

Figure 1. Location map of Florida.

1

comparable studies from western Florida donot exist. Interestingly, the west coastarea was the location of the seminalseagrass studies of Florida, inparticular, and the Southeast, in general.This work culminated in the monograph onthe seagrasses of Florida by Ronald C.Phillips published in 1960. Within thepast 10 years, research on these systemshas accelerated in the bays and estuariesof north Florida and in central Florida;however, less work has been done on thelarge offshore bed between these tworegions. This extensive seagrass meadowis unique among Florida's seagrassresources since it is truly offshore, anddoes not lie behind any form of protectivebarrier.

Seagrass ecosystems are among therichest, most productive, and mostimportant of all coastal systems. Theyare also paradoxical in nature--simultaneously simple and complex. Theyare simple in that there are few speciesof seagrasses, unique marine angiospermsthat live and carry out their life cyclein seawater. Vast and extensive underseameadows stretching for hundreds ofkilometers may be composed of only one toperhaps four species. The ecosystems,however, are complex ,because there arehundreds to thousands of species ofassociated flora and fauna that inhabitthe seagrass meadows and utilize the food,substrate, and shelter provided by theplants.

The pioneering work of Petersen (1918)in the Baltic region provided the firstdocumentation of the value of seagrassbeds to shallow coastal ecosystems. Thesestudies demonstrated how the primaryproduction from these plants was channeledthrough the detrital food web andsupported the rich commercial fisheries ofthe region. Despite the thoroughness andquality of Petersen's work, only in thepast two decades have the richness andvalue of seagrass ecosystems begun to berealized (Wood et al. 1969; McRoy andMcMillan 1977; Zieman and Wetzel 1980).The first conceptualization of thefunctions of seagrasses was provided byWood et al. (1969). The generalizationshave now been shown to be applicable to awide variety of systems and situations.The following is an updated version

(Zieman 1982) of the earlier conceptualframework.

1.

2.

3.

4.

5.

High Production and GrowthThe ability of seagrasses to exert a

major influence on the marine seascapeis due in large part to theirextremely rapid growth and high netproductivity. The leaves grow atrates of typically 5 mm per day, butgrowth rates of over 10 mm per day arenot uncommon under favorablecircumstances.

Food and Feeding PathwaysThe photosynthetically fixed energy

from the seagrasses may follow twogeneral pathways: direct grazing oforganisms on the living plant materialor utilization of detritus fromdecaying seagrass material, primarilyleaves. The export of seagrassmaterial, both living and detrital, toa location some distance from theseagrass bed allows for furtherdistribution of energy away from itsoriginal source.

ShelterSeagrass beds serve as a nursery

ground, that is, a place of both foodand shelter, for the juveniles of avariety of finfish and shellfish ofcommercial and sportfishingimportance.

Habitat StabilizationSeagrasses stabilize the sediments

in two ways: the leaves slow andretard current flow to reduce watervelocity near the sediment-waterinterface, which promotessedimentation of particles as well asinhibiting resuspension of bothorganic and inorganic material.Secondly, roots and rhizomes form acomplex, interlocking matrix withwhich to bind the sediment and retarderosion.

Nutrient EffectsThe production of detritus

promotion of sedimentationleaves of seagrasses provide

and theby theorganic

matter for the sediments and maintainan active environment for nutrientrecycling. Epiphytic algae on theleaves of seagrasses have been shown

2

to fix nitrogen, thus adding to thenutrient pool of the region. Inaddition, seagrasses have been shownto take up nutrients from thesediments, transporting them throughthe plant and releasing the nutrientsinto the water column through theleaves, thus acting as a nutrientpump.

In addition to providingshelter, the seagrass leavesfood resource in coastal

habitat andare a majorecosystems,

functioning through three major pathways:direct herbivory, detrital food webs, andexport to adjacent ecosystems. Directherbivory on green seagrass leaves isconfined to a small number of species andis most prevalent in tropical andsubtropical regions, especially in thevicinity of coral reefs. Since the timeof Petersen (1918), the detrital food webhas been considered the main trophicpathway in seagrass meadows, and currentstudies continue to support this concept,although direct herbivory can be locallyimportant in some areas (Zieman et al.1984a; Thayer et al. 1984). In additionto the internal utilization of seagrassesas a food source, many beds, especiallythose dominated by Syringodium, exportlarge quantities of organic material toother distant ecosystems.

In the subtropical waters of southFlorida, seagrass meadows often bridgelarge areas between the mangrove and coralreef communities, while also serving as aprimary nursery and feeding groundthemselves (Zieman 1982). On the westcoast of Florida, they function in asimilar manner, as nurseries and feedinggrounds, but also serve as an interfacebetween the coastal salt marsh communitiesand offshore habitats of the eastern Gulfof Mexico.

1.2 THESEAGRASSESOFTHEWESTCOASTOFFLORIDA

Seagrasses compose the relatively smallgroup of monocots which have evolved theability to carry out their life cyclecompletely submerged in the marineenvironment. Worldwide, they include 2families divided into 12 genera and

approximately 45 species. ThePotamogetonaceae include 9 genera and 34species and are represented on the westcoast of Florida by Syringodium filiformeKutz, whose common name is manatee grass,and Halodule wrightii Ascherson, shoalgrass; the Hydrocharitaceae contains 3genera with 11 species (Phillips 1978), ofwhich Thalassia testudinum Konig, (turtlegrass), and two species of Halophila, H.engelmanni Acherson and H. decipiensOstenfeld, are found in the waters of thewest coast of Florida. Ruppia maritimaLinneaus (widgeon or ditch grass)euryhaline angiosperm found abundantly infresh waters and in the marine environmentgrows primarily in lower salinity areas.

The small number of species occurring inthese waters, and their distinctive grossmorphologies (Figure 2) preclude the needfor a dichotomous key, although systematicworks such as den Hartog (1970) andTomlinson (1980) are available forcomparison of seagrasses in other areas.Phillips (1960a) still provides the besttreatment of local species.

The three dominant species of the opencoastal waters are Thalassia testudinum,Syringodium filiforme, and Halodulewrightii.

Thalassia is the largest and most robustof the west Florida seaarasses. and thedensest growth in the vast" grassded of theBig Bend area is dominated by a mixture ofthis species and Syringodium (Iverson andBittaker 1986). While this species is notabundant in the lower salinity waters ofTampa Bay (Lewis et al. 1985a), it is thedominant seagrass in the adjacent watersof Boca Ciega Bay (Taylor and Saloman1968; Bauersfeld et al. 1969), and in theTarpon Springs area (Phillips 1960a).

Among the local seagrasses, Syringodiumis distinctive in having cylindricalleaves which are quite brittle andbuoyant, and thus are readily broken offand exported from the immediate area bywinds and currents. This species is morewidely distributed in Tampa Bay than isThalassia (Phillips 1960a; Lewis et al.-and while it is codominant in theBig Bend grassbed, its biomass isgenerally lower than that of Thalassia inthe mixed stands of that area, although

3

Halodule wrightii

Syringodium filiforme

Thalassla testudlnum

Halophila engelmanni Halophila decipiens Ruppia maritima

Figure 2. The seagrasses of the west Florida coast.

there are localized areas where it isabundant.

Halodule, which has narrow leaves and ashmot system,pioneer species in

is recognized as thethe successional

development of grassbeds in the gulf andCaribbean. It is more tolerant of lowsalinity than both Thalassia and

Fyand thus occurs in areas of

ampa Bay where those seagrasses cannotsurvive1985a).

(Phillips 1960a; Lewis et al.As its common name, shoal grass,

indicates, it is often found in shallowwaters where it is subjected to repeated

4

exposure to the atmosphere. In the BigBend grassbed, this plant often forms boththe shallowest shoreward fringe of and thedeepest, outermost stands of seagrass, andexhibits different morphologies in the twozones (Phillips 1960b; McMillan 1978;R.L. Iverson, unpubl. data).

1.3 PHYSICAL ENVIRONMENT

The west coast of Florida has a mildmaritime climate varying from temperate inthe north to semitropical * thesouthernmost regions. For much':f the

year the southern portion of Florida isdominated by the southeasterly tradewinds, while the airflow in the northernand central portion is from the west,under the influence of the westerlies andaccompanying cyclones (counterclockwisecirculation about a center of lowpressure) in the winter, and the westernmargin of the Bermuda-Azores anticyclone(clockwise circulation about a center ofhigh pressure) in summer.

The resulting differences in temperaturepatterns are evident in Figure 3, whichshows the average monthly watertemperatures at several locations fromPensacola to Key West (McNulty et al.1972). The Cedar Key station is in thecenter of the region under considerationhere. Both the average and maximum summertemperatures vary little among thestations, with highs around 33 OC. Mostobvious are the lower winter temperaturesand greater seasonal range at the northernstations. Key West has a monthly lowaverage of 22 OC and a range of 14-26 OCduring January, while Cedar Key has a

January average temperature of 13.5 'Cwith a range of 4-22 OC.

Earle (1969) found a similar patternwith inshore gulf temperatures of 13-15 OCin the north and 22.6-22.9 OC in theFlorida Keys. However, north of CedarKey, extreme winter lows of O-5 OC havebeen recorded. The average wintertemperatures in the northern gulf inwinter are similar to the summer hightemperatures in New England, and Earle(1969) noted that many winter species inthe northern gulf are the same as thesummer species in New England waters.

Precipitation generally increasesnorthward and westward along the Floridacoast from a low of 100 cm annually at KeyWest to 163 cm at Pensacola (Table 1).However, in the region from Tampa toApalachicola the precipitation isrelatively uniform with a minimum annuallyof 118 cm at Cedar Key to a maximum of 140cm at Apalachicola with about half of theannual amount falling between June andSeptember. The average annual and monthly

Key West St. Petersburg Cedar Key PensacolaJ F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

Figure 3. Temperatures atfourlocations in coastal Florida (from McNulty eta11972).

5

Table 1. Precipitation statistics for coastal stations on the eastern Gulf of Mexico(from Jordan 1973).

Precipitation, Precipitation, Precipitation,Mean Annual June-Sept. Dec.-March(inches) G) G)

Mobile 65.5 41.4 34.9Pensacola 63.4 43.3 30.0Apalachicola 56.2 52.5 25.8Tallahassee 56.9 47.5 28.5Cedar Key 46.6 55.9 23.8Tampa 51.6 60.2 20.6Fort Meyers 53.3 63.6 14.3Everglades 54.7 62.5 12.4Key West 40.0 48.0 17.4

rates show the general patterns, but theextreme months and years are highlyvariable and can have severe effects onthe local biota. For Cedar Key, annualrainfall has varied between 68-208 cm,while monthly values at Apalachicola havevaried from a low of 0.03 cm to a high of57 cm.

In the shallow waters of the estuariesand the inshore gulf, water temperatureand salinity are locally affected by bothseasonal and isolated storms. The mostsevere storms are tropical hurricanes withtheir high winds, heavy rainfall, andoften devastating storm surges.Hurricanes occur most frequently in thelate summer months when the oceanicsurface temperatures are at their highest,but can occur in any month. Theprobability of encountering hurricaneforce winds in any one year varies greatlyalong the Florida coast, being 1 in 8 atKey West and Pensacola, 1 in 17 atApalachicola and St. Marks, and 1 in 25 atTampa-St. Petersburg (Bradley 1972). Inaddition to the immediate local effects ofthese storms, water quality is affectedfollowing their passage by greatlyincreased runoff from rivers and streams,accompanied by increased turbidity andbiochemical oxygen demand.

In most locations, seagrass beds arerelatively protected from the surges oflarge storms. However, in the Big Bend ofFlorida these beds are subject to the full

force of storm waves. In 1985, twohurricanes, "Kate" and "Elena" passeddirectly through the area causinglocalized disruption and bottom scouring.Qualitative observations of stationssampled before and after the hurricanessuqqested complete recovery of the denserinshore beds' of Thalassia, Syringodium,and Halodule and the sparse offshoreHalophila beds in the vicinity of TarponSorinas Shelf Associates1986):

(ContinentalIn the vicinity of Cedar Key,

where Hurricane "Elena" stalled for about48 hours, seagrasses appeared to berecovering, but at a slower rate than theother site.

Tidal ranges are low to moderate alongmost of the Florida west coast. FromFlorida Bay northward to St. Joseph Baythe tides are predominately semi-diurnal(McNulty et al. 1972), shifting to diurnalwest of this point. Throughout the entirearea, the mean diurnal range is 0.5-1.1 m.Daily ranges at Tampa Bay are 0.6-0.8 m.Just north of Tampa Bay, the rangeincreases to 1.1 m until Apalachee Baywhere it begins to decrease slightly andreaches 0.4-0.7 m at Apalachicola Bay.

Offshore circulation is dominated by twolarge counter-rotating gyres. Thenorthern one is influenced by coastalestuarine waters, while the southern oneis influenced by waters from Florida Bay.In addition, there are periodic incursionsof the loop current with waters from the

6

tropical Caribbean and the Yucutan Channel(Chew 1955; Austin 1970).

1.4 GEOLOGIC ENVIRONMENT

The present Florida peninsula is theemergent portion of the Floridan Plateau,consisting of layers of limestone andunconsolidated sediments over a base ofsandstone and volcanic rocks (Puri andVernon 1959; NcNulty et al. 1972). Thelimestone and ancient sediments are atleast 1,000 m in thickness over the entireregion. The rivers that. enter the gulfeast of Apalachicola Bay drain the coastalplain, carrying small amounts of sedimentsthat are primarily carbonates andanhydrites (McNulty et al. 1972). FromApalachicola Bay westward, the riversdrain areas of the Piedmont plateau andthe Appalachian highlands, and carry

primarily elastic sediments. Table 2gives the characteristics of sediments forseveral locations on the west Floridacoast.

The coastline of west Florida has beendivided and classified (Figure 4)according to several different criteriaand schemes, including coastal beach andinterface characteristics (Price 1954;Tanner 1960; McNulty et al. 1972), fauna1community affinities (Lyons and Collard1974), and underlying substrates andoutcrops (Brooks 1973). The coastaldivisions resulting from these differingschemes are very highly correlated, andthe divisions used in this paper are acombination of the above schemes.

The coastline west of Lighthouse Point,near Apalachicola Bay, is the northerngulf barrier coastline, with attached sand

Table 2. Sediment characteristics of the west Florida coast (from Folger 1972).

CarbonateLocation Organic content content Texture

Florida Bay

WhitewaterBay

Gullivan Bay(very open)

Port CharlotteHarbor

Tampa Bay

ApalachicolaBay

St. JosephBay

Pensacola Bay

Average = 2.1% west

1% on shelfl%-4% in lagoon

O.l%-1.0%maximum = 3.1%

0.5%-2.0%

0.5%-4.5%

__

up to 90%(Quartz 3.5% east,

up to 30%)

Up to 65%(quartz 5%-10%)

lo%-40% typicallyLocally to 60%-80%Quartz 4%-8% near

islandsmaximum = 24%

-_

0.5%-40%

lO%-40%

lo%-80%

1.3%-5%

Median size east = 0.025mmwest = 0.028mm

W = 70% silt, 30% sand

Non CaCOs = fine to veryfine sand

Very fine to fine sand

Variable, typicallysand sized

Variable, very coarsesand to clay

Variable, very coarsesand and gravel to clay

Coarse sand to silt

7

rend beaches and- low d u n s , o” G u l f ;

,;do, marshes and

c

Figure4. Coastalgeologyof the Florida west coast (from McNultyet al. 1972).

elasticbarrierfound to

beaches alternating with barrier islands. that they carry little suspendedA similar attached beach-barrier island material to form beaches orinterface exists from Anclote Key islands (Ross 1973) such as thosesouthward along the western edge of the the south or to the west.central and lower Florida peninsula.Along both the northern gulf and the Of equal or greater importancecentral and lower peninsula, the barrier the region between St. Marks ant_ .

is thatII Tarpon

beaches and spits enclose the majorestuaries and lagoons. However, the BigBend, the upper coastline of thepeninsula, is unique for the region inthat it is an extensive area with nooffshore barrier, where rivers, creeks,and marshes grade directly into theeastern Gulf of Mexico. A number ofphysical, geological, and hydrologicalfeatures interact to produce this effect.The rivers of the Big Bend are notable in

Springs is one of the few examplesworld-wide of a zero-energy coastline(Murali 1982). This is defined as a coastwhere "the average breaker heights are3-4 cm or less, and there is no signi-ficant littoral transport of sand" (Murali1982). The major factors that contributeto this phenomenon include the wide,gently sloping shelf; the divergence ofapproaching wave trains into the large,expanding coastal concavity; the location

8

of the coast in a generally upwind direc-tion; a small supply of new sediment; andthe wave dampening effects of old sub-merged beaches and the submerged seagrassmeadows (Murali 1982). Although thepresence of submerged seagrass meadowsinterfacing directly with salt marsheshas been considered to be a contributingfactor to the zero-energy coast, it ismore likely that their presence in thisarea is in fact the result of existing lowenergy conditions, as seagrass beds arerare on open oceanic, unprotected coasts.Once established, the seagrass beds couldenhance the effects of those primaryfactors responsible for reduced energyconditions.

1.5 SUCCESSIONANDECOSYSTEM DEVELOPMENT

Throughout their range, few plantsparticipate in the successional sequenceleading to seagrasses because there are sofew marine plants that can colonize softsediments. In general, this sequenceconsists only of the seagrasses and therhizophytic green algae. Seagrasses arevital to the coastal ecosystem becausethey are the only plants capable ofproviding the basis for a mature,productive ecosystem in these regions.Few other systems are so dominated andcontrolled by a single species as a climaxThalassia or Zostera meadow.

Odum (1974) classified Thalassia beds as"natural tropical ecosystems with highdiversity." Compared to other naturalsystems, tropical seagrass beds areregions of very high diversity, but thiscan be misleading. These comparisons weremade at a time when high diversity wasequated with high biological stability.The prevailing concept was that themultitude of different organisms, withtheir widely differing requirements andinteractions, functioned as a highlyintricate web structure that lessened theimportance of each link to the maintenanceof the total system. There was muchnatural redundance built into suchsystems. The problem is that at climaxthere is one species for which there is noredundancy - the seagrass. If theseagrass disappears, the entire associatedcommunity disappears along with it; there

is no other organism that can sustain andsupport the system.

The initial colonizers are typicallyrhizophytic macroalgae, of which variousspecies of Halimeda and Penicillus are themost common, although species of Caulerpa,Udotea, Rhipocephalus, and Avrainvillaoccur also. These algae have somesediment binding capability, but theirability to stabilize the sediments isminimal and their major function in theearly successional stage seems to be thecontribution of sedimentary particles asthey die and decompose.

Halodule wrightii, the local pioneerspecies of seagrasses, colonizes readilyeither from seed or rapid vegetativebranching. The carpet laid by Halodulefurther stabilizes the sediment surface;the numerous leaves forming a betterbuffer to protect the integrity of thesediment surface than the algalcommunities. In some sequencesSyringodium will appear next, intermixedwith Halodule at one edge of itsdistribution and Thalassia at the other.However, it is the least constant memberof this sequence and is frequently absent.In areas with consistent disturbance andsediments low . contentSyringodium may ber:me %Fniist abundantspecies. It is commonly found liningnatural channels with hiqh velocity watersand higher turbidity than Thalaisia cantolerate.

As successional development proceeds,Thalassia will begin to colonize theregion. Its strong straplike leaves andmassive rhizome and root systemefficiently trap and retain particles,increasing the organic matter of thesediment. The sediment height rises untilthe rate of deposition and erosion ofsediment particles is in balance. This isa function of the intensity of waveaction, current velocity, and leafdensity.

In shallow-water successional sequencesleading to Thalassia, the early stages areoften characterized by low sedimentorganic matter and open nutrient supply;that is, the community relies on nutrientsbrought in from adjacent areas by watermovement as opposed to in situ- -

9

regeneration. With the progression fromrhizophytic algae to Thalassia, there is aprogressive increase in the below groundbiomass of the community as well as theportion exposed in the water column. Withthe progressive increase in leaf area ofthe plants, the sediment trapping andparticle retention increases. Thismaterial adds organic matter to furtherfuel the sedimentary microbial cycles.

In summary, as species succession occursin these shallow marine systems, importantstructural changes occur. The mostobvious change with community developmentis the increase in leaf area, which

provides an increase in surface area forthe colonization of epiphytic algae andfauna, with the surface area of the climaxcommunity being many times that of eitherthe pioneer seagrass, Halodule, or theinitial algal colonizers. In addition toproviding a substrate, the increasing leafarea also increases the leaf baffling andsediment trapping effects. Thus, as thecanopy component increases, so does thematerial in the sediment. Thalassia, theclimax species, has the highest leaf area,the highest total biomass, and by far thegreatest amount of material in thesediments of any of the successionalstages.

10

CHAPTER 2. AUTECOLOGY OF FLORIDA GULF COAST SEAGRASSES

2.1 PLANT MORPHOLOGY AND GROWTH

Seagrasses worldwide show a remakablesimilarity in their structure and growth(den Hartog 1970; Zieman and Wetzel 1980).For the seagrasses of the northwest coastof Florida, we shall focus primarily onthe growth and morphology of Thalassia,considering this as representative of thelocal species.

Detailed descriptions of the anatomy andmorphology of Thalassia were presented byTomlinson and -966) and Tomlinson(1969a, 1969b, 1972). Flat, straplikeleaves with rounded tips emerge from erectshort shoots which branch laterally fromhorizontal rhizomes at regular intervals.In this species rhizomes occur from 1 to25 cm below the sediment surface, but aretypically found in the depth range of3-10 cm. (The rhizomes of Halodule andHalo hila are near the surfamften& While the rhizomes ofSyringodium are generally found at anintermediate depth, in strong currents,they may be exposed, even extending upinto the water column.) Roots ofThalassia emerge from the rhizomes and theshort shoots. Much smaller in crosssection than rhizomes, the roots vary inlength according to sediment compositionand depth.

On a Thalassia short shoot, new leavesgrow on alternating sides of a centralmeristem that is enclosed by old leafsheaths. New growth on leaves is producedby the basal meristem, thus the base of aleaf is the freshest, youngest portion.

this species typicallyShort shoots ofhave two to five leaves at a time.

Studies ofmorphology havetemporal and spat

seagrass growth andrevealed patterns of

ial variation. Grassbeds

11

in areas of relatively low productivity inBiscayne Bay, Florida, averaged 3.3 leavesper short shoot, while in the moreproductive meadows of the Florida Keys,plants averaged 3.7 leaves per short shoot(Zieman 1975a). The width of leavesincreased with age of the short shoot,reaching maximum width five to sevenshoots back from the growing rhizome tip(Figure 5). Leaf width can also reflectmorphogeographic variation: in Florida,Durako and Moffler (1981) identified theeffects of a latitudinal stress gradientin leaves of Thalassia seedlings, with thegreatest widths occurring in the Keys andthe narrowest leaves found in northernFlorida. In another study, leaf widthsdid not reflect a latitudinal or stressgradient, but showed sexual differences:female short shoots tended to havenarrower leaves than male shoots (Durakoand Moffler 1985a). Transplantexoeriments found that narrow-leavedplants of Thalassia, Syringodium, andHalodule from the north coast of the Gulfof Mexico continued to produce narrowleaves, and broader-leaved plants from thesouthern gulf and Caribbean likewisecontinued to produce wider leaves, evenwhen moved to different habitats (McMillan1978).

Thalassia leaves in Biscayne Bay grew anaverage of 2.5 mm/day in length, butgrowth rates as high as 1 cm/day weremeasured over periods of 15-20 days(Zieman 1975a). Leaf growth rate inThalassia usually decreases exponentiallywith leaf age (Patriquin 1973; Zieman1975a). In contrast, leaf elongation inSyringodium proceeded at a relativelysteady rate throughout the growth phase(Fry 1983). The first few leaves producedon a new Thalassia short shoot are reducedin size and are tapered; the regularstraplike leaves are produced at a rate of

AVERAGE LEAF WIDTH (MM)

8 5 8 7 7.5 7 4

L E A F

BRANCH ORS H O R T S H O O T - .

DISTANCE BETWEEN BRANCHES (CM)

Figure 5. General morphology of a Thalassia plant.

one-new-leaf-per-short-shoot every 14-16days. The rate of leaf production inBiscayne Bay was dependent on temperature,with low growth occurring in the coolerwinter months (Zieman 1975a). Lessseasonal variation was found in thetropical Caribbean waters of Barbados andJamaica by Patriquin (1973) and Greenway(1974) respectively. Durako and Moffler(1981) found a gradient of root and leafgrowth in Thalassia seedlings, from highrates in the Florida Keys to low growthrates in north Florida waters.

In Tampa Bay, Durako and Moffler (1985c)found pronounced seasonal patterns inmaximum leaf lengths of Thalassia. Therewas a slight decrease in the middle ofsummer, coincident with high temperaturesand floral production, but maximum lengthswere much less in the cold winter months,reflecting both leaf die-off and depressedgrowth rates due to exposure to lowtemperatures. A pattern of spatial

variation was evident, with shorter leavesoccurring in the middle of the grassbedwhere the water was shallower.

2.2 REPRODUCTION

Vegetative reproduction in seagrassesaccounts for their capacity to producehigh biomass and area1 cover; however,sexual reproduction is important inproviding the genetic plasticity forsuccessful adaptation and competition inthe species. Studies of flower productionin the seagrasses considered here havefocused primarily on Thalassia. Thisplant is sexually dimorphic, producingseparate male and female flowers. Greyand Moffler (1978) found that short shootsoccurring on a common rhizome segmentproduced flowers of the same sex,suggesting that Thalassia is alsodioecious, that is, has separate male andfemale plants.

12

Flower production in Florida populationsof Thalassia occurs from April to Augustor September, peaking in June (Orpurt andBoral 1964; Grey and Moffler 1978) (Figure6). While Phillips (1960a) found noflowering north of Tarpon Springs, morerecent studies have revealed flowering inthe grassbeds of the Florida panhandle(Marmelstein et al. 1968; Phillips et al.1981). The percent of short shoots in agrassbed bearing reproductive structuresvaries greatly: less than I_% of plantsfrom north Florida beds reproducedsexually, while reproductive densities inplants from south and central Floridaranged from l% to 15% (Phillips 1960a;Orpurt and Boral 1964; Zieman 1975). Morerecently Moffler et al. (1981) foundreproductive densities of 44% in TampaBay. A later study in Tampa Bay recordedreproductive densities of 11.4%, 20.7%,and 10.0% for 1981, 1982, and 1983,respectively, and found that increasednumbers of male flowers accounted for thehigher reproductive density of 1982(Durako and Moffler 1985b). Spatialdensity distributions showed highernumbers of female plants occurred on the

fringes of the bed where short shoots aregenerally younger, while more male plantswere found in the center on presumablyolder short shoots. This pattern couldreflect an age-related sexual expressionin the plants, although environmentalfactors and clonal differences also caninfluence leaf width (Durako and Moffler1985b). (Thalassia seed production inTampa Bay was apparently low compared withsouth Florida and probably could notprovide an adequate supply for restorationprojects (Lewis and Phillips 1981).

Phillips (1960a) found flowering Ruppiaabundant in Tampa Bay; however, he did notobserve seedling germination. Flower andfruit production in Ruppia of this areapeak in May and disappear in June (Lewiset al. 1985a). Phillips (1960a) did notfind reproductive Halodule, Syringodium,or Halophila in Tampa Bay; however,several reproductive specimens of Halodulewere later found in nearby waters (Lewiset al. 1985a). Although reproductiveplants are rare in Syringodium, femaleplants have been collected in the bay(Lewis et al. 1985a). Zimmerman and

Figure 6. Flowers of Thalassia (left) and Syringodium (right) (photo by M. J. Durako.)

13

Livingston (1976b) found a number offlowering Syringodium plants in theirApalachee Bay samples in May, 1972. Theseauthors also found numerous floweringplants of Ruppia in May and June.

In 1 aboratory studies, cultures ofThalassia, Syringodium, Halodule, andHalophila engelmannii flowered undercontinuous light, suggesting thatflowering was independent of day length.The temperature range for flowering inthese plants was 22-26 OC (McMillan 1982).Lewis et al. (1985a) also found thatflower production in Thalassia wasprobably controlled by factors other thanphotoperiod.

2.3 PLANT CONSTITUENTS

Because of their high productivity andwide distribution, seagrasses arerecognized as a potentially important foodsource in shallow coastal marine systems.The fact that this abundant food source issubjected to relatively low levels ofdirect grazing on the living plantmaterial has prompted studies of thechemical constituents and relative foodvalue of seagrasses. Various authors haveperformed such constituent analyses forthe seagrasses considered here(Burkholder et al. 1959; Bauersfeld et al.1969; Walsh and Grow 1972; Lowe andLawrence 1976; Bjorndal 1980; Dawes andLawrence 1980; Vicente et al. 1980; Dawesand Lawrence 1983). A summary of theseresults is given in Table 3. Dawes andLawrence (1980) noted that the differencesin sample preparation and chemicalanalyses employed make direct comparisonof the data difficult, and subsequentlyproposed a procedure to standardizeanalyses so that future data will becomparable, making it possible todetermine the effect of seasonal and otherenvironmental changes on the chemicalcontent of the plants.

The relative amount of protein in theplant tissues has been used as a measureof the potential food value of tropicalseagrasses. Comparative studies haveshown that turtle grass leaves are roughlyequal in percent protein to phytoplanktonand Bermuda grass (Burkholder et al. 1959)and 2 to 3 times higher than 10 species of

tropical forage grass (Vicente et al.1980).

Walsh and Grow (1972) found thatThalassia protein content comparedfavorably with reported values for graincrops: corn contained from 9.8% to 16%protein, sorghum 8.6% to 16.5%, and wheat8.3% to 12%. Various studies of theprotein content of Thalassia leaves haveyielded results ranging from a low of 3%of dry weight for unwashed epiphytizedleaves (Dawes et al. 1979) to a maximum of29.7% for leaves rinsed with .distilledwater (Walsh and Grow 1972). The lowvalue for unwashed leaves reflects theinclusion of sea water salts, and possiblysediment particles which settle on leaves,into the total dry weight. Values moretypically range between 10% and 15% of dryweight.

Dawes and Lawrence (1983) and Durako andMoffler (1985c) have reported spatial andtemporal variations of protein content.In Tampa Bay values for Thalassia andS rin odium varied from 8% to 22% and from*, respectively, with maximumvalues occurrinq in the summer (Table 4).Thalassia leaves collected in July 1979from Tamna Bav. Kev West. and GloversReef, Belize,-' showed a significantincrease in protein content from Tampa toBelize, even though the sites were similarin depth, salinity, and temperature (Dawesand Lawrence 1983). If such a latitudinaltrend holds, Thalassia from the Big Bendarea, for which constituent analyses havenot been performed, could have even lowerprotein content, and thus lower foodvalue. Such a decrease in nutritionalvalue might be reflected in the results ofKitting et al. (1984), who found thatseveral seagrass "detritivores" in thenorthern gulf actually derived most oftheir nutrition from epiphytes.

The new growth of the basal portions ofleaves of Thalassia are higher in proteinand lower in Inorganic content (Cawes andLawrence 1980). The green turtle has beenshown to exploit this fact in its patternof grazing: a patch of seagrass isinitially cropped, with the upper olderportions of the leaves left to float away,and such patches are subsequentlymaintained for a period of time byrepeated grazing (Bjorndal 1980). Thus,

14

Table 3. Constituent analysis of seagrasses (from Zieman 1982).

Season/ % as Carbo-Species Component date Referenced Ash

EnergyNitrogen Protein Fat hydrates (kcal/g) Reference

Thalassia Leaves February %DW 24.8 2.1 (13.1) 0.5 35.6 1.99 Burkholderet al. 1959

Annual %AFDW 1.6-4.8 25.7mean %DW 24.5 (10.3-29.7)

JanuaryAprilJulyOctoberMean

%DW 29373344x

8 0.99 4.0

22 1.0

23.6 4.66 Walsh andGrow 1972

?

455044

2.4 Dawes and3.0 Lawrence3.1 1980

41 2.6E 2.8

1313

2 022.0

%DW(unwashed)%DW(washed)

47.3 11.0 0.7

13.0 0.5

38

24.8 35.6

%DW 24.7 9.1 2.3 63.9

Bauersfeldet al. 1969

July-August

Lowe andLawrence1976

JanuaryAugust

%DW 16.7 Bjorndal1980

17 Vicenteet al.1978

(Continued)

Table 3. (Continued).

Species ComponentSeason/ % as Carbo- Energydate Referenced Ash Protein Fat hydrates (kcal/g) Reference

Thalassia Rhizomes

Roots

Photosynthesisinactive partof short shoot

Rhizomes

Syringodium Leaves

Leaves

Short shootsphotosynthesisinactiveparts

Annualmean

JanuaryAprilJulyOctoberMean

JanuaryAprilJulyOctoberMean

July-August

JanuaryAprilJulyOctoberMean

JanuaryAprilJulyOctoberMean

%DW%AFDW%DW

23.8

50.524.1

5.8-12.211.019.615.0

72.1

%DW 395148567E

9 1.07 0.5

16 0.78 0.8

lo 0.8

51 2.742 2.235 2.535 2.0a 2.4

%DW 26243336m

9 0.5 65 3.28 1.6 66 3.4

16 0.2 51 3.07 1 1

i-0A0.9

56 2.8m 3.1

%DW 27.0 3.10 3.4 66.3

%DW 30283332x

9 1.7 598 6.2 58

13 4.0 5013ii

1.83.4

53!Z

%DW 28 10 1.3 6127 11 3.6 5831 14 0.9 5441 11 1.1 47Z? Tz 1.7 !Z

4.88 Walsh and Grow 1972

Bauersfeld et al.1969

Dawes and Lawrence1980

Lowe and Lawrence1976

3.1 Dawes and Lawrence2.4 19803.23.13.0

3.23.33.12.63.1

(Continued)

Table 3. (Concluded).

Species ComponentSeason/ % as Carbo-date Referenced Ash Protein

EnergyFat hydrates (kcal/g) Reference

January %DW 16 9April 18 5July 17 12October 19 6Mean 18 8

1.0 74 3.64.7 72 3.70.1 71 3.60.51.6

75 3.573 3.6

Syringodium Rhizomes

January %DW 32April 25July 25October 26Mean T

JanuaryAprilJulyOctoberMean

%DW 25293634Ti

JanuaryAprilJulyOctoberMean

%DW 14

17 8i-G 8

19 1.0 4818 3.2 5419 1.2 55

Halodule Leaves 3.1 Dawes and Lawrence3.5 19803.33.33.3

14T;s

1.41.7

5955

Short shootsphotosynthesisinactive part

59898

1.13.50.81 2A1.7

6959555660

3.23.02.92.93.0

Rhizomes 0.71.60.11 1;0.9

76747074T-4

3.73.73.43.63.6

Table 4. Seasonal content of protein and soluble carbohydrates (% dry weight) in Tampa Bay (afterDawes 1987).

Species Component January April July October

Thalassia testudinum

Leaves Protein 8Carbohydrate 6

99

229

137

Protein 9 8 16 7Carbohydrate 12 21 24 36

Rhizomes

Syringodium filiforme

Leaves 1320

Protein 9 8 13Carbohydrate 22 16 18

Protein 9 5 12 16Carbohydrate 36 38 50 46

Rhizomes

Halodule wrightii

Leaves Protein 19 18Carbohydrate 14 19

1915

1413

Protein 9 7 8 8Carbohydrate 43 40 43 54

Rhizomes

higher levels of soluble carbohydrates inThalassia rhizomes compared to the leaves.In Tampa Bay, seasonal variation insoluble carbohydrate content occurred inthe rhizomes of both Thalassia andSyringodium, reflecting production andstorage of starch during summer and fall(Dawes and Lawrence 1980). Mean valuesfor the lipid content of Thalassia leavesvaried from 1.2% to 4.2%, and werecomparable to the "fat" content oftropical terrestrial grasses.

the turtles create a more energeticallyand nutritionally rich food source, and,indeed, Zieman et al. (1984) found thatthe nitrogen content of leaves withinturtle patches was similar to the contentof the basal portions of ungrazed leavesand higher than the upper portions ofthose leaves.

The values reported for ash content ofThalassia leaves range from 45% dry weightfor unwashed samples to a low of about 25%for samples rinsed in fresh water.Samples washed in ambient seawatercontained 29%-44% ash (Dawes and Lawrence1980). Thalassia rhizomes from the westcoast of Florida had ash contentsignificantly lower than did the leaves,with mean values ranging from 2l% to 26%dry weight (Dawes and Lawrence 1983).Cell wall carbohydrates (cellulose,hemicellulose, and lignin) accounted for45%-60% of the dry weight of turtle grassleaves (Bjorndal 1980; Vicente et al.1980). Dawes and Lawrence (1983) found

2.4 PHYSIOLOGICAL ECOLOGY

2.4.1 Environmental Tolerancesand Responses

a. Temperature. The range of thermaltolerance in tropical organisms isoften about half that of theirtemperate counterparts. Althoughthe upper temperature limits aresimilar, the tropical organisms have

18

reduced cold tolerance. McMillan(1979) found a gradient of chilltolerance in Florida seagrasses,with those from northern Floridamost tolerant of low temperaturesand those of the Florida Keys leasttolerant. After growing in culturefor 22 months, Thalassia seedlingsmaintained their original pattern ofchill tolerance: those fromApalachee Bay, Florida, showed lessdamage than seedlings from theFlorida Keys and St. Croix.

In the thermally impacted watersof Anclote Estuary north of TampaBay, Barber and Behrens (1985) foundthat maximal growth in Syringodiumoccurred between 23 and 29 OC, andbetween 23 and 31 OC in Thalassia(Figure 7). In the cooler months,thermally impacted stations hadhigher productivities than didnon-impacted areas, but in thesummer months, Syringodiumproductivity was depressed at thewarmer stations when the upperthermal tolerance limit of thisseagrass was exceeded. In ApalacheeBay, Zimmerman and Livingston(1976b) found that Syringodiumtolerated lower temperatures thanThalassia, which suffered leaf killwhen temperatures fell below 15 OC.Some defoliation of Thalassia alsooccurred when summer temperaturesrose to 30 OC.

Thalassia

IO 15 20 25 30

TEMPERATURE (“C)

Figure 7. Temperature responses of ThalassiaBehrens 1985).

In Texas waters, vigorous growthof Ruppia in the spring correlatedwith cool temperatures rather thanlowered salinities (Pulich 1985).Phillips (1960a) reported atemperature range of 7-35 OC forRuppia in Tampa Bay; growth andreproduction was highest with springtemperatures, and decreased whenhigh summer temperatures werereached. In Texas, a similar patternof temperature response was evidentfor Ruppia in a mixed stand withHalodule; in contrast, Halodulebiomass at that site peaked in thewarmer summer months and declined inthe fall. Phillips (1960a) reportedthat Halodule in Tampa Bay sufferedwinter leaf kill, even at siteswhich were always submerged.However, Halodule suffered littleleaf kill in Apalachee Bay, wherethe minimum winter temperature was 9OC. This temperature was a newminimum reDorted for HaloDhilaen elmanni (Zimmerman and Livingstoni!kijT

b. Salinity. Although the seagrassesconsidered here are able to toleratefluctuations in salinity, theoptimum concentration for growthvaries among the species.Experiments with transplantedseagrasses showed that, of thespecies considered here, Halodulehad the broadest salinity tolerance,

4.0

3.0

2.0

1.0

Syrinqodium0

1 1 1 I10 15 20 25 30 35

TEMPERATURE (“C)

and Syringodium on the west Florida coast (after Barber and

19

/ -

Thalassia and Syringodium(==E;c$;;ea)t;eere intermediate, and

most stenohaline.Ruppia sho;;im a wide tolerancz:ranging freshwaterhypersaline conditions (McMillan1974). Evaluating the upper limitsof salinity tolerance, McMillan andMosely (1967) found that Halodule(=Diplanthera) tolerated the highestsalinities, surviving up to 80 ppt,followed, in order, by Thalassia,Ruppia, and Syringodium, withHalophila's relative toleranceaoparentlv somewhere betweenHalodule -and Syringodium McMillan

salinities was Ruppia, followed byHalodule, Thalassla, Syringodium(=Cymodocea), and Halophila. Whileboth Ruppia and Halodule exhibitbroad ranges of salinity tolerance,the former is the only seagrassspecies, of this region capable ofsurviving in freshwater. Accordingto McMahan (1968), Halodule does notsurvive in salinities less than 3.5ppt and has an optimum salinity of44 ppt.

Thalassia and Syringodium do notgrow in areas of low salinity in theeastern Gulf of Mexico (Phillips1960a), and were not reported inareas with salinities less thanabout 17 ppt in the northernseagrass bed (Zimmerman andLivingston 1976). Turtle grass cansurvive short periods of exposure toextremes ranging from a low of 3.5ppt (Sculthorpe 1967) to a maximumof 60 ppt (McMillan and Mosely1967); however, significant leafloss frequently follows exposure tosalinity extremes. The optimumsalinity reported for this seagrassranges 24-35 ppt (Phillips 1960;McMillan and Mosely 1967; Zieman1975a). In turtle grass, maximumphotosynthetic activity occurred infullstrength seawater, and decreasedlinearly with decreasing salinity(Hammer 1968b). The effect offreshwater runoff following ahurricane was considered moredamaging to seagrasses than the

effects of high winds and tidalsurge (Thomas et al. 1961).

According to Humm (I973),Halophila does not tolerate reducedsalinities; however, Zimmerman andLivingston (1976b) found a bed of y.engelmanni off the mouth of theEconfina River, an area ofrelatively low salinity.addition, Earle (1972) report::Halophila occurring at depthsranging from intertidal to 13 m, andStrawn (1961) found this speciesmixed with Halodule and Ruppia on anold oyster bar. Thus, it appearsthat tialophila may in fact be quiteeuryhaline.

Ruppia traditionally has beenconsidered a brackish-water species(Verhoeven 1975) and, indeed, amongthe seagrasses it alone can bemaintained in tap water (McMillan1974). Phillips (1960a) reportedthat it occurred most frequently insalinities below 25 ppt, whichcorrespond with the findings ofZimmerman and Livingston (1976b).In the Big Bend seagrass bed, Ruppiawas observed growing near rivermouths (R.L. Iverson, Forida StateUniversity, Tallahassee; pers.comm.) However, Dawes (1974) foundit growing in areas of relativelyhigh but stable salinity in thelower portions of Tampa Bay.transplants

Ruppiasurvived in salinities

up to 74 ppt (McMillan and Mosely1967); this species also grew inTexas waters at a site wheresalinities averaged 25-32 ppt and at

hypersalinefor several

another site whereconditions persistedmonths (Pulich 1985).has been observedhypersaline waters in(J. Fourqurean, Un

a l s oRuppiagrowing inFlorida Bay

iversity ofVirginia, Charlottesville; pers.comm.). Thus Ruppia also appears tobe quite euryhaline.

The oxygen contained in thecolumn of seagrass beds

generally provides a supply adequateto meet the respiratory demands ofthe plants themselves and associatedorganisms. In Thalassia beds,

20

photosynthetic oxygen production canbe so high that bubbles escape fromthe leaf margins in the lateafternoon. The seagrasses are lesssusceptible to low oxygenconcentrations than the animals ofthe grassbeds; nevertheless, leafmortality and increased microbialactivity coincided with loweredoxygen levels in Japanese Zosterabeds (Kikuchi 1980). Low 0s levelsdo slow their rate of respiration,and when internal O2 concentrationsare lowered, the plant's rate ofresgiration is controlled bydiffusion of oxygen from the watercolumn. During the night, therespiratory demand of the seagrassesand associated plant and animalcommunities can lower concentrationsof the surrounding waters (Durako etal. 1982). In Puerto Rico (Odum etal. 1960) and in Florida and Texas(Odum and Wilson 1962) nighttimeoxygen concentrations were typically4-7 mg 0s L-l, and a low of 2-3 mg02 L-l recorded on a calm night inAugust during an extreme low tide.

d. Light.The fact that well-developedseaarass beds do not occur at depthsgreater than 10 m has beenconsidered indirect evidence thatphotosynthesis in seagrassesrequires high light intensity, andthat light penetration limits thedepth to which seagrasses can grow(Humm 1956; Buesa 1975; Wiginton andMcMillan 1979). Gessner and Hammer(1961) suggested that increasedhydrostatic pressure, as well asdecreased light, may limitphotosynthesis suggesting that lightis probably not the sole factorrestricting photosynthesis at depth;however, there were no significantpressure effects on photosyntheticrates of Thalassia and Syringodiumfor plants collected from variousdepths near Buck Island, St. Croix,and subjected to 1 and 3 atmospheresof pressure (R.L. Iverson,Department of Oceanography, FloridaState University; unpubl. data). It

therefore unlikely that thei:essures that exist over the depthgradients where these seagrasses arefound can explain the significant

decrease in Thalassia biomass atthe limit of its depth distribution.However, the maximum depth at whichseagrasses occur does indeedcorrelate with the available lightregime. Buesa (1975) reported thefollowing depth maxima for theseaarasses off the northwest coastof _ Cuba:Syringodium,decipiens 24englemann;, 14.

Thalassia16.5 m;

.3 m; and4 m.

14 m;HalophilaHalophila

Of the visible light spectrum, thelonger red wavelengths are absorbedin the first few meters in bothclear and turbid waters. The cleartropical waters of the Caribbean Seaare enriched in blue light, while inturbid shallow waters, such as partsof Florida Bay and coastal waters ofTexas, enrichment of greenwavelength occurs. In a study ofthe effects of specific wavelengthsof light on seagrass photosynthesis,Buesa (1975) found that Thalassiaresponded best to red light-)and S rin odium grew best with bluewave-0 nm). Wiginton andMcMillan (1979) reported increasingchlorophyll a to chlorophyll bratios for seagrasses obtained fromincreasing depths near Buck Island,St. Croix, but concluded that lightquantity rather than light qualitywas the primary environmentaldeterminant of seagrass depthdistribution along the Buck Islandgradient. Thalassia growing inouter Florida Bay has considerablymore non-photosynthetic tissue than

compensation light-energy level(below which annual net increase oftotal plant biomass cannot occur)for Thalassia growing in tropicalhabitats is less than thecompensation light energy level forSyringodium and for Halodule as aconseauence of thedemands

respiratorycreated by the 'greatei

orooortion of nonohotosvnthetictissue mass of Thalassia <n thosehabitats.

Humm (1973) observed that Ruppiaoccurred in areas of low light and

21

high turbidity. Phillips (1960a)also noted the growth of thisspecies in areas of poor lightpenetration.in addition to!%$!$%ng~~light of deeper waters also grows inareas of high turbidity (Zimmermanand Livingston 1976b).

e. Current. Seagrass biomass andproduction are greatly influenced bycurrent velocity (Conover 1968).The maximum standing crops for bothThalassia and Zostera were foundwhere current velocities averaged0.5 m set-l. Rapid currents arethought to disrupt diffusiongradients and increase theavailability of CO2 and nutrients tothe plants (Conover 1968). In southFlorida, the densest stands ofThalassia and Syringodium are foundin the tidal channels separatingmangrove islands. Off the coast ofNicaragua, samples from mangrovetidal channels had a leaf standingcrop of 262 g dry weight m-2 andtotal biomass of 4,570 g m-2. Bycomparison, values for samples froma quiescent lagoon were 185 and1,033 g m-2 respectively (McRoy,Zieman, and Ogden, unpubl. data).

Strong currents can affect thestructure of seagrass beds. In someareas of high current, lunatefeatures called blowouts occur(Patriquin 1975). Thesecrescent-shaped erosional featuresmigrate through the bed in thedirection of the current.Recolonization takes place at thetrailing edge of the blowout, andhere the successional sequence ofseagrass colonization can beobserved.

f. Sediment. Seagrasses are found in avariety of substrates, ranging intexture from fine muds to coarsesands. Because they are rootedplants, they do have minimumsediment-depth requirements, whichdiffer among the species.Halodule's shallow surficial rootsystem allows it to colonize thinsediments in areas of minimalhydraulic stability (Fonseca et al.

1981). Thalassia is more robust,reauirina up to 50 cm of sedimentfor lush-growth, although it occurs

shallowerG72).

sediments (ZiemanIn the Bahamas, Thalassia

did not occur in sediments less than7 cm deep (Scoffin 1970). Phillips(1962) reported that seagrasses inTampa Bay grew only in muddy sandsubstrates, and patches of pure sandwere unvegetated.

Reduced sediments seem always tobe associated with well-developedThalassia beds and most likelyreflect the greater importance ofsediment-nutrient content andmicrobial nutrient recycling inmeadows of this species, rather thana specific requirement for reducingconditions. Halodule is generallythought to grow in more aerobicsubstrates; however, Pulfch (1985),working in Texas waters, postulatedthat Ruppia normally occurs inlow-nutrient sediments whileHalodule prefers organic-richsediments where sulfate reduction issubstantial. Phillips (1960a)reported that Syringodiumdistribution was apparentlyindependent of sediment type andthis species is found in bothoxidized and reduced sediments(Patriquin and Knowles 1972).Ruppia is generally found in finersubstrates than the above species(Phillips 1960a), while Halophilagrows in a wide range of substratesfrom muddy sands to limestone, andeven on mangrove roots (Earle 1972).

In the Big Bend area of the westcoast of Florida, Iverson andBittaker (1986) also recordedThalassia growing in coarsersediments than the other species ofthat northern grassbed. Syringodiumand Halodule biomass were greater infine sediments (Iverson and Bittaker1986). Similarly, Buesa (1975)found that Thalassia off thenorthwest coast of Cuba grew incoarser sediments than Syringodiumor Halophila.

g. Exposure. Thalassia and Syringodiumare subtidal plants and do not

22

tolerate exposure to the air. WhileThalassia does grow on flats thatare infrequently exposed, unlesssuch exposure is brief, desiccationwill cause leaf kill. Halodule canwithstand repeated exposure at lowtide, and is most abundant betweenneap-low and spring-low tide marks

higheriG6Oa).

salinities (PhillipsIn low-salinity intertidal

areas, Ruppia and Halodule oftenoccur in mixed stands (Phillips1962; Earle 1972). Dawes (1987)noted that Ruppia forms extensivemeadows on flats where it can beexposed to intense sun and appearsto tolerate a degree of desiccation.

2.4.2 Photosynthetic Carbon Fixation

Three separate biochemical pathways bywhich plants can fix inorganic carbonphotosynthetically have been identified.The majority of terrestrial plantsutilize the Cs pathway, in which CO2 isinitially incorporated into a three-carbon product. In the C, pathway, foundprimarily in plants from tropical andarid areas, a four-carbon product resultsfrom the first step of CO;! incorpora-tion. The third pathway, CAM (crassula-cean acid metabolism), by which plantstake up CO:! at night and store it asmalic acid until daytime when it is thenused in photosynthesis, occurs in water-stressed plants such as desert succu-lents. A major factor in the differencesof photosynthetic physiology between Csand C4 is the greater efficiency ofrefixation of photorespired CO2 found inthe C, plants (Hough 1974; Moffler et al.1981). High rates of refixation havebeen detected, however, in some Cs plantswith specialized leaf anatomy and gaslacunae (Sondergaard and Wetzel 1980) andmay be implicated in seagrass carbonmetabolism (Beer and Wetzel 1982). Sea-grass leaves possess large internallacunar spaces which facilitate gastransport (Zieman and Wetzel 1980). Thepresence of these lacunae and the absenceof stomata provide the plants with arelatively closed pool of carbon dioxide,thus promoting recycling of CO*.

Seagrasses share with C4 plants suchphysiological adaptations as high thermaland light optima for photosynthesis and

high productivity rates. AlthoughThalassia was originally thought to be aC, plant, Beer and Wetzel (1982), usingradiolabel led HCOm3, concluded that boththis seagrass and Halodule wereintermediaries between Cs and C4 in theircarbon metabolism. Syringodium andZostera exhibited the most typically Cspattern of the seagrasses studied.

2.4.3 Isotopic Fractionation

A significant result of the differencesin carbon metabolic pathways is thatimprints are left in the form ofcharacteristic ratios of the stableisotopes of carbon in the plant tissuesproduced. In biochemical reactions,plants do not utilize 12C and 13C in theexact ratios found in the environment,but discriminate between the two,favoring the lighter isotope. Plantsusing the C3 pathway are relativelydepleted in 13C, while C4 plants havehigher ratios of l3C to l2C. Therelative content of 1% to 12C iscompared to the isotopic ratio of astandard and expressed as a "del" value(6) as follows:

13C/l2C(513c, sample lx103

13c/12cstandard

The range of 613C values for Cs plantsis -24 to -34 ppt, while C4 plants varyfrom -6 to -9 ppt (Smith and Epstein1971). Seagrass values, particularlythose of Thalassia and Syringodium, aresimilar to those of the C4 plants.McMillan et al. (1980) reported that 45of 47 species examined fell within therange of -3 to -19 ppt, with only twospecies of Halophila having lower values.Samples of Thalassia from the Gulf ofMexico and the Caribbean range from -8.3to -12.5 ppt, with a mean of -10.4 ppt.Halophila had similar isotopiccomposition, with means of -10.2 ppt forgulf and -12.6 ppt for Caribbean samples.Syringodium, by comparison, hadrelatively fewer negative numbers, with amean of -5 ppt and a range of -3 to -9.5PPt. This species has a greaterproportion of lacunar spaces, and thelacunae are more completely partitionedthan those of the other seagrassesconsidered. This greater lacunar

23

isolation presumably enhances therecycling of C02, which occurs in C,plants! and thus the similarity inisotopic composition is not unexpected.Tropical seagrasses in general havevalues less neaative than those oftemperate specie;. A study of Zosterashowed little seasonal variation inisotopic composition (Thayer et al.1978). The isotopic composition canvary, however, with habitat (Smith et al.1976; Zieman et al. 1984c). McMillan andSmith (1982) found that seagrasses grownin laboratory cultures had more negativevalues, that is, were more depleted inthe heavier 13C than samples from thenatural environment. They concluded thatsuch results could reflect differences incarbon sources and in recycling ofinternal carbon.

Since plants have characteristicisotopic compositions, and the animalsthat consume them retain to within t2 pptthe same ratio (DeNiro and Epstein 1978;Fry et al 1978), these isotope"signatures" provide a useful tracer forfood chain studies (Figure 8). In themarine environment, seagrasses haveisotopic ratios distinct from othermarine plants. Thus carbon derived fromseagrasses (-3 to -15 ppt) isdistingished from that of marinemacroalgae (-12 to -20 ppt), particulateorganic carbon and phytoplankton (-18 to-25 ppt) and mangroves (-24 to -27 ppt)(Fry and Parker 1979). In Texas,sediment organic matter within a seagrass

bed was more depleted in 13C compared tosediment organic matter from adjacentbays without seagrasses (Fry et al.1977), and the same pattern was reflectedin the animals (Fry 1981). The 6 13C ofthe polychaete worm Diapatra cupreavaried from an average of -13 ppt inseagrass-dominated areas to -18 ppt wherephytoplankton were the dominant primaryproducers (Fry and Parker 1979). Similartrends were observed for fish and shrimp.

The utility ofmethod of foodrestricted at thecost of analyticallimitations of data

this carbon isotopechain analysis ispresent by the highequipment and by theinterpretation. When_^

a consumer organism has a 6 l"C valuewhich falls within a range specific for aparticular plant source, the relationshipis readily apparent; however, if theanimal has a de1 value falling betweentwo identifiable pl,ant groups, it isunclear whether this represents a foodsource which itself has a valueintermediate between the two known groupsor whether the organism is consuming amixed diet.

2.5 NUTRIENTUPTAKEANDSUPPLY

Seagrasses are highly productive plantsthat can grow in low-nutrientenvironments; thus, the manner in whichplant nutrient demands are met is ofparticular interest. Since seagrassesoccupy both the water column and the

CARBON ISOTOPE ANALYSIS OF PRODUCERS AND CONSUMERS

6 13c

ROOKERY BAY ---- T H PA PP ELMM

PINE CHANNEL ---- S P P T H L A MM

! 11 ll! lrrl!llrl!ll rl!llll!

-5 -10 -15 -20 -25 -30

Legend: T = Thalassia P = Pink Shrimp E = Epiphytes M = Mangroves L = Litter A = MacroalgaeH = Halodule S = Syringodium

Figure 8. Carbon isotopic variation at two locations in Florida (after Zieman et al. 1984c).

24

sediments, controversy existed in thepast over whether nutrients were taken inthrouah the leaves or the roots. Thetempeiate seagrass Zostera is capable oftakina in nutrients both from the watercolumi and through the roots (McRoy andBarsdate 1970); however, uptake throughthe root system was shown to be fasterand more efficient (Penhale and Thayer1980). McRoy and Barsdate (1970) foundthat Zostera could translocate ammoniumand phosphate from the sediments to theleaves and excrete these nutrients intosurrounding waters. Such nutrientpumping may be important only insediments with high nutrientconcentrations (Penhale and Thayer 1980).

Studies of nutrient supply toseagrasses have concentrated on nitrogenand phosphorus because these, along withcarbon, are the primary constituents ofplant material. In Zostera beds inChesapeake Bay, the addition ofcommercial fertilizer containing bothnitrogen and phosphorus stimulated leafgrowth (Orth 1977a). Harlin andThorne-Miller (1981) observed similargrowth enhancement when inorganicammonium and phosphate were added towaters overlying Zostera beds in a RhodeIsland bay. The relative importance ofthese major nutrients in limiting plantgrowth has not been determined andprobably depends on local nutrientsupplies and processes.

Three sources of nitrogen are availableto the plants: microbially recyclednitrogen from organic matter in thesediment, dissolved ammonium and nitratein the water column, and ammonium fromthe microbial fixation of dissolved NZ.Sources of organic matter fordecomposition in the sediment includeanimal excretions and dead roots andrhizomes, Sediment bacteria convert theorganic nitrogen to ammonia in the anoxiczone, which begins only a few millimetersbelow the surface. Ammonia that is notquickly bound either by biological uptakeor chemical adsorption by sedimentparticles can diffuse upward to theaerobic zone, where it can then diffuseinto overlying waters or be converted tonitrate by nitrifying bacteria. Nitrateconcentrations are low in the sediments;nitrate is either rapidly assimilated or

converted to N2 by denitrifying bacteria.Patriquin (1972) and Capone and Taylor(1980) identified the recycled organicmaterial as the primary source ofnitrogen for leaf growth; however,nitrogen fixed by sediment microbescould supply 20% to 50% of the plants'requirements (Capone and Taylor 1980).In contrast, Capone et al. (1979) foundthat fixation by phyllosphere microbescontributed primarily to epiphyte growth.The relative importance of the differentnitrogen pools to the plants is indicatedby such factors as sedimentcharacteristics and water columnconcentrations.

Inorganic phosphorus, unlike nitrogen,has no gaseous phase and does not changevalence state in normal environmentalreactions. Thus the source of phosphorusto the seagrasses is dissolved inorganicorthophosphate (PO,), derived either fromthe breakdown of organic matter or fromthe weathering of minerals, some of whichare biologically precipitated. Whilewater-column concentrations in tropicalwaters are normally low, phosphate may bequite abundant in the sediments. Highlevels of HCl-extractable phosphate werefound in the carbonate sediments ofseagrass beds of Barbados, but pore-waterconcentrations and concentrations inoverlying waters were low (Patriquin1972). Because the high sedimentconcentrations probably reflectedundissolved phosphate not available foruptake by the plants, Patriquin concludedthat the nutrient-poor overlying waterswere the primary source of phosphate tothe seagrasses. Sediment type influencesthe dissolution of phosphate, and,therefore, its availability to theplants. Silicious sediments readilyexchange phosphate with overlying waters(Nixon et al. 1980), but carbonatesediments tend to absorb phosphate,removing it from solution. Rosenfeld(1979) reported that pore-water phosphateconcentrations of Florida Bay sedimentswere two orders of magnitude lower thanconcentrations in Long Island Sound porewaters and attributed the difference tocalcium carbonate adsorption ofphosphate.

Terrestrial runoff also can be animportant factor affecting the

25

concentration of dissolved nutrients. In limiting plant growth can be expected toApalachicola Bay, nutrient concentration vary accordingly. At this time, thepeaks coincided with periods of maximum degree to which phosphorous and nitrogenriver discharge (Myers and Iverson 1981). are limiting the growth of Florida'sThe bays and estuaries of the northwest seagrasses is still unknown, and is acoast of Florida vary widely in sediment timely and important topic for furthercomposition and terrestrial input; thus, research.the supply of phosphate and its role in

26

CHAPTER 3. DISTRIBUTION, BIOMASS, AND PRODUCTIVITY

3.1 DISTRIBUTION

Distribution of seagrasses along thewest coast of Florida is unique in thatthe plants not only occur in protectedestuarine grassbeds typically found alongthe Gulf of Mexico coast (represented inthis area by the grassbeds in embaymentssuch as Rookery Bay, Charlotte Harbor,Tampa Bay, and St. Joseph Bay), but alsoform an extensive offshore bed locatedalong the coastal reach between the St.Marks River and Tampa Bay, known as theBig Bend area.

have been studied most extensively (Thorne1954; Phillips 1962; Taylor and Saloman1968; Lewis and Phillips 1980; Lewis etal. 1985a). While this estuary hasreceived intense human impact and cannotbe considered necessarily typical orrepresentative of west Florida bays, theabundance of information on Tampa Bayseagrasses provides a useful base forcomparison with other areas.

Seagrass distribution in the easternGulf of Mexico has been investigated atseveral different levels of spatialresolution. Humm (1956) reportedseagrasses observed at specific sitesalong the northern coast of the Gulf ofMexico. Phillips (1960a) described thegeneral location of seagrasses around theGulf of Mexico based on literature reportsand on field surveys. Bauersfeld et al.(1969) and Earle (1972) estimated area1seagrass distribution in the eastern Gulfof Mexico using indirect methods. McNultyet al. (1972) reported seagrassdistribution within embayments andestuaries in the eastern Gulf of Mexicobased on field observations and onanalysis of aerial photography. While theseagrass distribution within embaymentsadjacent to the northeastern Gulf ofMexico has been reasonably well described,the spatial extent and biomass ofseagrasses of the Big Bend area have beenonly recently investigated (ContinentalShelf Associates 1985; Iverson andBittaker 1986).

Thorne (1954) identified five seagrassesoccurring in the bay: Thalassia, Syringo-dium, Halodule, Ruppia maritima and Halo-philae n g e l m a n n i i . In his survey of sea-grasses of Tampa Bay, Phillips (1962)reported the presence of all species butHalophila; however, this seagrass waslater observed in the bay by Lewis andPhillips (1981) and Moffler and Durako(reported in Lewis et al. 1985a).Phillips (1962) noted that the southernpart of the bay was dominated by Diplan-athera (Halodule) and in the northernpart Ruppia was more abundant, presumablydue to a salinity gradient. Thalassia isrelatively sparse in Tampa Bay, possiblybecause of low salinities (Phillips 1962),but is the dominant species in the adja-cent waters of Boca Ciega Bay (Pomeroy1960; Phillips 1962; Taylor and Saloman1968). Lewis et al. (1985a) estimatedthat the current distribution of sea-grasses in the bay, covering 5,750 ha(14,203 acres) represents a reduction of81% of historical coverage prior to humanimpact (Figure 9).

3.1.1 Seagrass Distribution in Tampa Bay

a. Seagrass associations. There arefive types of seaqrass meadows foundin Tampa Bay (Figure 10). Mid-bayshoal perennial beds contain Tha-lassia, Syringodium, and Halodule,but rarelv RuoDia. due to either the

Among the estuarine grassbeds of thewest coast of Florida, those of Tampa Bay

fast currents or increased salini-ties found on the shoals where these

27

10 mi

15 km

Figure 9. Seagrass coverage in Tampa Bay in 1879 and 1982 (after Lewis et al. 1985).

beds grow. Healthy fringe perennialbeds contain all five species foundin the bay. In these beds, Ruppiais found in the shallowest waterclose to shore, followed by almostpure stands of Halodule, Thalassia,and Syringodium, respectively, asdepth increases. These meadowsgenerally have an unvegetated sandbar separating the seagrasses fromthe main body of the bay. Stressed-fringe perennial beds are similar totheir healthy counterparts exceptcoverage is reduced, and migrationof a destabilized sand bareventually leads to the dis-appearance of the bed. These bedsoccur in areas of the bay wherephytoplankton are abundant, possiblycompeting with the benthicmacrophytes. Finally, colonizingperennial grassbeds are found inbands in the euphotic zone of man-made fill areas. The dominant soe-ties here are Halodule and Syringo-dium, presumably because their rhi-

zomes are more readily fragmentedand dispersed to unvegetated areas.

b. Sediment effects. According toThorne (1954) seagrass distributionin the Gulf of Mexico was limited tosoft marl, mud, or sand substrates.Phillips (1962) found that all sea-grasses in Tampa Bay grew in muddysand: while sandy substratesremained unvegetated. The sedimentsof the bay contain varying amountsof carbonates, which may be impor-tant in determining the availabilityof essential nutrients.

C. Depth distribution. Phillips (1962)reported that seagrass growth waslimited to depths of less than onefathom (2 m) in the turbid waters ofTampa Bay. Syringodium dominatesbelow the spring low-tide mark, and indeeper water frequently occurs inmixed stands with Thalassia (Humm1956; Phillips 1960a; Phillips 1962).Shallow areas are dominated by Ruppia

28

MBS(P)

HF(P)

S F (PI

Figure 10. Seagrass meadow types in Tampa Bay.MBS(P) = mid-bay shoal perennial; HF(P) = healthyfringe perennial; SF(P) q stressed fringe perennial; Eq ephemeral; C(P) = colonizing perennial (after Lewiset al. 1985).

and Halodule (Phillips 1962). ThreemOrDhOl oaicallv distinct forms ofHalbdule-in the bay were identifiedaccording to depth distributionDwarfed plants occurred in areasexposed at neap and spring low tides,while subtidal plants were more robust(Phillips 1960d). Salinity ratherthan tidal exposure was thought tocontrol the distribution of Ruppia inthe bay (Phillips 1962).

3.1.2 Seagrass Distribution inthe Big Bend Area

The Big Bend seagrass bed overliesdrowned karst topography which extendsfrom the town of St. Marks south to TarponSprings. The sediments of this low energyregion are composed of clay and silicioussand over limestone. Results of recentinvestigations suggest that seagrasses arethe dominant benthic feature of the

nearshore environment from St. Marks toTampa (Iverson and Bittaker 1986;Continental Shelf Associates 1985)Analysis of a photographic compositeobtained from aerial photography(Continental Shelf Associates 1985)revealed some broad-scale patterns inseagrass distribution with beds ofgreatest density in shallow water wellremoved from river mouths. Beds of lesserdensity extended as far as 112 km offshore(Figure 11).

Samples for characterization of seagrassdistribution in eastern Gulf of Mexicocoastal waters were taken by Iverson andBittaker (1986) from St. Marks to Tampaduring the month of October for severalyears. Visual observations of thepresence or absence of different seagrassspecies were made at each of about 300stations in the Big Bend area of northFlorida (Figure 12). Samples forestimation of seasonal seagrass biomasschanges were collected within a 10 mradius of a metal marker stake located in1 m water depth at stations near theFlorida State University Marine Laboratoryat Turkey Point, and in St. Joseph Bay.

The line marking the outer limit of theseagrass beds in Figure 12 indicates themaximum depth to which seagrass coverageof about 80% or more of the bottomextended within each major area.Vegetation covered about 3,000 km*, withseagrasses occurring as a band varyingfrom 11 to 35 km wide between St. Marksand Tarpon Springs, Florida.

All six species of seagrasses presentedin Chapter 1 were found in the Big Bendgrassbeds. Halodule occasionally formedboth the innermost and the outermostmonospecific stands in this area.Shallow-water Halodule growing on shoalsoften exposed at low tide, generally hadshort, narrow leaves, and deep-waterHalodule was tall with wider leaves(Iverson and Bittaker 1986).Shallow-water and deep-water forms ofHalodule appear to be morphologicallydifferent clones (Phillips 1960b; McMillan1978). Shallow areas not exposed on lowtides contained mixtures of Thalassia,Syringodium, and Halodule. Densestportions of the seagrass bed weredominated by Thalassia and Syringodium in

29

‘7.-CRY5

Bl:TAL

Y

Figure 11. Seagrass distribution and density in the Big Bend area (adapted from Continental ShelfAssociates 1985).

30

OUTER LIMIT OFSEAGRASS BEDS

29” N+EM0 w

GULF OF

5 0 k i l o m e t e r s

SrSteinhatchee

;PRINGS

casassa

PHOTO TRANSEC’I -.%?=Y

I * 1

SEAGRASS PRESENT0 Thalass ia testudinum

Q Syrlngodium f i l i f o r m e

(3 Halodule wriahtii

Q Halophila enqelmanni

Q Halophtla decipiens

Q Rupp ia mar i t ima9m. MLW -c-y“

a

Figure 12.1986).

Seagrass species distribution in the Big Bend area (after lverson and Bittaker

31

various mixtures. Halophila engelmanniwas common in this orassbed. and was oftenmixed with Thalassia and Syringodium.Halophila engelmanni was also abundantoutside the major seagrass bed to depthsof at least 20 m where it occurred inmonotypic stands (Continental Shelf Asso-ciates. 1 9 8 5 ) . Halophila decipiensoccasionallv occurred in small monotvoicstands or mixed with sparse Halodule'orCaulerpa populations in northern offshoreareas deeper than 5 m, as well as in someof the shallowest areas (Continental ShelfAssociates 1985). Ruppia was primarilyrestricted to low salinity areas such asthe mouths of the Econfina and SuwanneeRivers.

a. Depth distribution control. Iversonand Bittaker (1986) showed that themajor seagrass species were distri-buted throughout the seagrass bedsin mixed associations (Figure 12),in contrast to south Florida, wherelarge monospecific beds are far morecommon. Thalassia and Syringodiumcomprised most of the biomass whichextended to about 5 m water depth.Halodule wrightii and Halophilaengelmanni contributed very littleto total seagrass leaf biomass.

A transect taken across a grassbednear the Florida State UniversityMarine Laboratory showed that Tha-lassia was present in greatest leafbiomass at depths between 0.5 and2 m, while Syringodium reachedgreatest leaf biomass at 2.5 m(Figure 13). Halodule occurred atboth ends of the transect (Iversonand Bittaker 1986). The generalpattern in fine-scale depth distri-bution of seagrass species appearsto be similar among the variousAmerican tropical seagrass beds forwhich observations have beenreported. Strawn (1961) describedthe cross-bed, seagrass distributionnear Cedar Key in the northeast Gulfof Mexico. Halodule occurred inmonotypic stands on shoals exposedto the atmosphere at low tide andwas distributed throughout the sea-grass bed. Thalassia grew only insubtidal areas and did not extend tothe deepest limits of the bed whichcontained Syringodium. This depth

ThalassiaB -qi HaloduleSvrinaodium

I 2 3 4DEPTH (m)

5oor T

DEPTH (m)Figure 13. Depth distribution of seagrass biomassin Apalachee Bay (after lverson and Bittaker 1986).

distribution pattern was evident inseveral diverse areas: in the grassbed samples in northern ApalacheeBay (Iverson and Bittaker 1986), inthe northwest Cuban seagrass bed(Buesa 1974), in a Nicaraguan sea-grass bed (Phillips et al. 1982),and in a seagrass bed near BuckIsland, St. Croix (Wiginton andMcMillan 1979).

32

For many kilometers along theouter limit of the Big Bend seagrassbed between Tarpon Springs andCrystal River, an observer on thewaters' surface notices a distincttransition from the dark green outeredge of the seagrass bed and thelight sediment bottom seaward of thebed edge. The outer edge of thegrassbed is deeper north of TarponSprings, in the Big Bend bed, com-pared with the part between St.Marks and the Crystal River. Thisvariation is a consequence ofincreased water clarity in thesouthern part of the Big Bend sea-grass bed, as indicated by theextinction coefficients for lightenergy in the water column measuredin those areas. In addition, sub-jective observations made over aperiod of years suggest that therelative differences in waterclarity from the two areas are con-sistent (R.L. Iverson, unpubl.data). The nearshore waters of theBig Bend area receive river runoffcolored(Bittaker $75) o$?~~c

compoundsin addition

to particulates, contr\butes to theincreased turbidity and higherextinction coefficients observed inthat area (Zimmerman and Livingston1979).

Based on the depth-distributiondata obtained in several differentinvestigations, the light-energycompensation level for the annualgrowth of American tropical seagrasscommunities dominated by Thalassiaappears to be about 10% of sea-surface photosynthetically activelight energy. The depths to which10% of sea-surface light energypenetrated, calculated from measuredextinction coefficients, were 7 mfor the part of the seagrass bedbetween Tarpon Springs and CrystalRiver, and 4.5 m for the portionnorth of Crystal River. Thesedepths,approximate the seaward limitof the major seaqrass beds comoosedof Thalassia, -Syringodium, ’ andHalodule in those respective areasof the eastern Gulf of Mexico.Although Thalassia and Syringodiumwere distributed to greater depths

in Cuban coastal waters (Buesa 1974)and in St. Croix waters (Wigintonand McMillan 1979) compared with theBig Bend area and Florida Bay, mostof the leaf biomass in the northwestCuban and the Buck Island, St.Croix, seagrass beds was locatedshallower than the depth to which10% of surface light energy pene-trated. The maximum possible areain which Thalassia can form well-developed beds appears to be con-strained by the slope of the seafloor and the bottom depth of theisolume corresponding to 10% ofsurface light energy (Iverson andBittaker 1986).

b. Salinity and temperature effects.The nearshore species composition ofseagrass assemblages in the northernbed is influenced by freshwater dis-charges entering the northeasternGulf of Mexico from several riversalong the coast. Thalassia testu-dinum and Syringodium filiforme donot grow in areas of low salinitvwater in the northeastern Gulf o?Mexico (Phillips 1960a) and were notreported in areas with salinitiesless than about 17 ppt in thenorthern seagrass bed (Zimmerman andLivingston 1976a).

The seagrasses of the Big Bendarea experience a large temperaturerange (8-33 "C) (Goulet and Haynes1978). Seagrasses from this bedwere more tolerant of very cold tem-peratures than were seagrasses fromFlorida bay (McMillan 1979; McMillanand Phillips 1979); however, eachwinter, leaves of Big Bend sea-grasses die back to within severalcentimeters of the sediment-waterinterface (Zimmerman and Livingston1976b), a phenomenon also observedin seagrass beds in Texas watersduring cold winters (Phillips 1980).

C . Sediment effects. Thalassia grew incoarser sediments than did the otherseagrasses of the Big Bend area(Iverson and Bittaker 1986). Buesa(1975) reported that Thalassia innorthwest Cuban grassbeds also grewin coarser sediments than did otherseagrasses.

33

Sediment deposition on leaf sur-faces significantly interferes withthe growth of both Thalassia testu-dinum and Halodule wrightii(Phillips 1980). Water turbiditywas inversely related to distancefrom the Econfina River mouth(Bittaker 1975; Zimmerman andLivingston 1979), suggesting thatturbidity effects on seagrass growthoccur primarily nearshore as pro-posed by Humm (1956). Moore (1963a)reDOrted that hiah-water turbiditvprecluded the griwth of Thalassiatestudinum in Louisiana coastalwaters within the Mississippi Riverplume.

3.2 BIOMASS

Seagrass biomass can vary greatlydepending not only on the species but onsuch environmental variables as availablelight, sediment depth, nutrient avail-ability, and circulation. The biomass ofHalophila is always low, but Thalassiabiomass can reach values greater than 7 kgm-2 (Burkholder et al. 1959). Ranges ofbiomass values for Thalassia, Syringo-dium, and Halodule are presented in Table5. The results of many of these studieshave been summarized by various authors(McRoy and McMillan 1977; Zieman andWetzel 1980; Zieman 1982; Thayer et al.1984b; Lewis et al. 1985a). Since thestudies involve a wide range of experi-mental conditions, including differencesin habitat, sampling times and seasons,and sample replication, attempts to com-pare or generalize based on the cumulativedata are of questionable value.

The majority of seagrass biomass,particularly in the larger species, isbelow the sediment surface. Ordinarily,15%-20% of Thalassia's biomass is in theleaves (although reported values rangefrom 10% to 45%) with the rest made up byroots, rhizomes, short shoots, andsheathing leaves (Zieman 1975, 1982).Sediment type can affect the relativeamount of biomass above and below thesurface: the ratio of leaf to root andrhizome biomass in Thalassia increasedfrom 1:3 in fine mud to 1:5 in mud and 1:7in coarse sand (Burkholder et al. 1959).It is unclear whether this reflects

enhanced leaf production in nutrient-richer fine sediments or the need forgreater root development for increasednutrient absorption in the aenerallvpoorer coarse sediments. Thalassia hasthe most robust root and rhizome svstem ofthe seagrasses of Florida. Halodule andSyringodium have shallower, less well-developed roots and rhizomes, and tend tohave a greater portion of their totalbiomass, 50% to 60%, in leaves (Zieman1982). However, Pulich (1985) reportedthat Halodule from Redfish Bay, Texas had66% of total biomass below the sedjmentsurface, compared to 3l.% for Ruppia.Reported values for the relative portionsof' above- and below-ground biomass inFlorida west coast species are shown inTable 6.

3.2.1 Seagrass Biomass in Tampa Bay

Both above- and below-ground biomass ofthe seagrasses of the bay were determinedby Lewis and Phillips (1980). Ruppia hadthe lowest biomass, both for standing crop(portion of plant above sediment surface)and root and rhizome (below sediment sur-face). Thalassia had the highest below-ground biomass, but its leaf standing cropwas similar to that of Syringodium.

In nearby Boca Ciega Bay, Thalassia leafstanding crop exhibited seasonal varia-tion, reflecting temperature extremes.Dry weights peaked in spring and earlysummer, declined during mid-summer tem-perature maxima, and dropped to the lowestvalues during winter months (Phillips1960a). Durako and Moffler (1985c)observed a similar seasonal pattern inmaximum leaf lengths of Thalassia in TampaBay. Seagrass biomass for the Tampa Bayarea, as reported by Lewis et al. (1985a),is given in Table 7.

3.2.2 Seagrass Biomass inthe Big Bend Area

Thalassia and Syringodium comprised 84%of total leaf biomass in the Big Bendarea; Thalassia alone accounted for 58% ofleaf biomass compared to 64% for grass-beds in Florida Bay (Iverson and Bittaker1986). Thalassia leaf biomass reached aseasonal maximum during August and thendeclined rapidly at stations located nearthe Florida State University Marine

34

Table 5. Representative values of seagrass biomass (g dry weight m-*1.

Species Biomass Location Source

m a r i t i m aRuppia

Halodule wrightii60-160

10-400

22-208

10-300

Syringodium filiforme15-1100

30-70

Thalassia testudinum30-500

60-718 Puerto Rico

60-250 Texas

20-1800 Florida (eastcoast)

57-6,400 Florida (westcoast)

Texas

Texas

North Carolina

South Florida

South Florida

Texas

Cuba

Pulich 1985

McMahan 1968;McRoy 1974;Pulich 1985

Kenworthy 1981

Zieman unpubl.

Zieman unpubl.

McMahan 1968

Buesa 1972,1974;Buesa andOleachea 1970

Burkholder et al.1959; Margalef

and River0 1958

Odum 1963;MCRoy 1974

Odum 1963; Jones1968 ;

Zieman 1975b

Bauersfeld et al.1969; Phillips1960a; Taylor etal. 1973a

Laboratory and in St. Joseph Bay (Figure with significant blade densities, the14). The seasonal effect is related to density decreased by over 50% at 7 of 11cycles of light intensity and water tem- stations in the winter months. Mostperature (Iverson and Bittaker 1986). The stations that showed no difference or aratios of seasonal maximum to seasonal slight increase had only sparse seagrassminimum values at these sites were between cover.6:l and 8:1, showing the difficulty ofcomparing sites on the basis of biomass The seagrass beds of St. Joseph Bay aredata, particularly in higher latitudes primarily composed of Thalassia testudinumwhere seasonal patterns are more pro- growing in monospecific stands. McNultynounced. Continental Shelf Associates et al.(1985) found that for offshore stations

(1972) estimated 2,560 ha ofseagrass coverage within St. Joseph Bay.

35

Species

Table 6. Biomass partitioning In seagrasses.

Biomass % ofComponent (g dry wt m-*> Total Reference

Ruppiamaritima

Above groundBelow ground

Above groundBelow ground

Halodulewrightii

Above groundBelow ground

Above groundBelow ground

Syringodium Above groundfiliforme Below ground

Thalassiatestudinum

Above groundBelow ground

11050

4848

150290

5-54 11-3310-200 67-89

28-102 16-4731-521 53-84

58-267 11-15321-2,346 85-90

6931

5050

3466

Pulich 1985a

Lewis andPhillips 1980

Pulich 1985

Zieman 1982

Zieman 1982

Zieman 1982

aPeak seasonal biomass values.

Table 7. Seagrass biomass of the Tampa Bay area (g dry wt mm*) (from Lewis et al. 1985a).

SpeciesBiomass

Location Above ground Below ground Reference

Ruppia maritima Tampa Bay

Halodule wrightii Tampa Bay

Syringodium filiforme Tampa Bay 50-170

Thalassia testudinum Boca CiegaBayBird KeyCat's PointBoca CiegaBay

32.432598

636

320-1,198

601-819

25-180

Tarpon Springs

Tampa Bay

1.48 18-48

38-50 60-140

160-400 Lewis andPhillips 1980

48.6

Bauersfeld etal. 1969

Taylor andSaloman 1969Dawes et al.1979

600-900 Lewis andPhillis 1980

Lewis andPhillips 1980

Lewis andPhillips 1980

Pomeroy 1960Phillips 1960aPhillips 1960a

A M J J A S O N DMONTH

Figure 14. Seasonal cycle of Thalassia at twostations in Apalachee Bay(after lverson and Bittaker1986).

Another estimate of St. Joseph Bayseagrass coverage obtained during 1978 was2,300-2,400 ha of coverage, suggestingthat seagrass beds are a stable feature ofthe benthos of St. Joseph Bay and are notmarkedly affected in spatial coverage byseasonal cycles in leaf biomass density(Savastano et al. 1984). Iverson andBittaker (1986) found that short-shootdensities did not change significantlythroughout the year, and suggested that,during the fall of the year, the use ofshoot densitiescomparisons wouldthis area.

for interbed biomassbe more appropriate for

3.3 PRODUCTIVITY

The high rates of primary productivityof seagrasses is well recognized. Studiesof biomass literature have reported a widespectrum of productivity measurements(Table 8). Past studies have focused on

Table 8. Seagrass productivity measurements.

SpeciesProductivity

(g C m-2 day-l) Site Reference

Halodulewrightii 0.5- 2.0 North Carolina

1.1 Florida (eastcoast)

Syringodiumfiliforme 0.8- 3.0

0.6- 9.0

Thalassiatestudinum 0.6- 7.2 Cuba

2.5- 4.5 Puerto Rico1.9- 3.0 Jamaica0.5- 3.0 Barbados

FloridaTexas

0.9-16.0 Florida (eastcoast

Dillon 1971

Virnstein 198Za

Zieman unpubl.Odum and Hoskin1958; McRoy 1974

Buesa 1972,1974Odum et al. 1960Greenway 1974Patriquin 1972b;1973Odum 1957,1963;Jones 1968; Zieman1975a

aCalculated as 38% of reported dry weight.

37

Thalassia, but more recently Halodule andSyringodium have been studied.

A major problem encountered in attemptsto synthesize the results of various pro-ductivity studies is that the three majormethods of measurement--leaf marking, O2evolution, and l*C uptake --each yieldsomewhat different results. In theliterature, the highest values areobtained using the O2 method, the lowestvalues result from leaf marking, while 14Cmeasurements provide intermediate values(Zieman and Wetzel 1980; Kemp et al.1986). In a carefully developed study,Bittaker and Iverson (1976) found that 14Cand leaf marking gave essentially identi-cal results when the 14C results werecorrected for inorganic losses, incubationchamber light absorption, and differencesin light energy resulting from differencesin experimental design. In a study ofThalassia in Bimini, Capone et al. (1979)found, however, that productivity measuredby the 14C method was double the ratesobtained from the leaf marking technique(Zieman 1974; Fry 1983) which underesti-mates net productivity since it does not

measure below-ground productivity,excreted carbon, or herbivory. The 14Cmethod allows the investigator to deter-mine the partitioning of photosynthatewithin the plant. Figure 15 shows thelocation of 14C in Thalassia after a4-hour incubation period. The leavescontained 49% of the radiocarbon althoughthey made up only 13% of the total bio-mass.

Despite the methodological differences,studies of the productivity of seagrasseshave shown that these are highly produc-tive systems, especially when growingunder optimal or near-optimal conditions.

3.3.1 Seagrass Productivity in Tampa Bay

Surprisingly little data exist on theproductivity of the seagrasses of thisarea. In nearby Boca Ciega Bay, Pomeroy(1960) estimated that Thalassia andSyringodium occurring at depths less than2 m, fixed 500 g C.m-2. yr-I. He con-cluded that, at these depths, seagrasses,microflora, and phytoplankton were equallyimportant primary producers, whereas

sheath

rhizome

roots

% Total 14C u p t a k e % Total weight

.:.n

49.0

2 3 . 3 34.1

2 6 . 6 5 0 . 3

I ,I 3 . 3

13.3

Figure 15. Location of recently fixed carbon photosynthate in Thalassia after4 hour incubation. The right handcolumn shows the typical weight distribution in the plants (after Bittaker and lverson 1976).

38

phytoplankton production dominated indeeper waters. Johansson et al. (1985)estimated that phytoplankton productivityin Tampa Bay was higher in deep waters(340 g C.m-2. yr-l) than in shallow waters(50 g C.m-2. yr-l), and concluded that, incontrast to the results of McNulty (1970),phytoplankton production was ten timeshigher than benthic production in the bay.

Studies of Thalassia leaf growth inTampa Bay show that leaf lengths canincrease at a rate of 5 cm per monthduring the period of maximum growth in thespring. Maximum leaf length occurs inearly summer, before high temperaturescause a mid-summer die-back (Lewis et al.1985a).

3.3.2 Seagrass Productivity inthe Big Bend Area

A seasonal cycle was evident inmacrophyte carbon-production data obtainedover a period of several years at astation in the northern part of the BigBend area (Figure 16). Thalassiatestudinum contributed most of the carbonproduction per unit area (up to2.2 g C.m-2.d-1 in July), except for abrief midsummer period when red driftmacroalgae were the largest source ofphotosynthetic carbon fixation. Data fromwhich these composite carbon productionfigures were made were taken from Bittaker(1975), who showed that the annual carbonproduction cycle was related to annualvariations in solar radiation and watertemperature.

Near the Anclote River, seagrassproductivity estimated from leaf growthmeasurements was reported as 2-15 mgC.m-2.h-1 for Thalassia, 2-37 mg C.m-2.h-1and 0.9-1.4 mg C m-L h-l for Syringodiumand Halodule, respectively (Ford 1974 etal .; Ford and Humm 1975).

I -

THALASSIA(a)

OTHER SEAGRASSES

I

d!tbkiI

RED MACROALGAE

(cl

I=

I-

l-

I

‘ J F M A M J J A S O N

M O N T HFigure 16. Seasonal changes in productivity ofseagrasses and red algae in Apalachee Bay(unpublished data from Ft. L. Iverson).

39

CHAPTER 4. COMPONENTS OF THE SEAGRASS COMMUNITY

The distribution and density of seagrassspecies are dependent on the physical,chemical, and geological environment,while the associated community is theproduct of this seagrass composition aswell as the abiotic variables. Along thewest coast of Florida, from Florida Bay toApalachicola Bay, there are largevariations in all of the majorphysico-chemical parameters. Thisenvironmental gradient is reflected in thechanges of species associations andcommunity structure within the seagrasssystem.

Although it is obvious that largechanges in abiotic variables and plantcomposition and density can produce majorchanges in the community structure, evensubtle variations apparently can producemajor community differences. At fivesample sites in a single south Floridaestuary with Thalassia blade densities ofover 3,000 m-2 the total number ofmacrofaunal taxa'varied from 38 to 80, andthe average density of individuals variedover two orders of magnitude, from 292 to10,644 individuals m-2 (Brook 1978).

Organisms found in seagrass communitiescan be classified in a number of ways,depending on the objectives of theclassification. The biota present in aseagrass ecosystem can be classified in ascheme that recognizes the central role ofthe seagrass canopy in the organization ofthe system, and classifies the organismsaccording to their position relative tothe canopy. The principal groups are:(1) epiphytic organisms, (2) epibenthicorganisms, (3) infaunal organisms, (4) theplanktonic organisms, and (5) the nektonicorganisms.

and Zieman (1982) as any sessile organismgrowing on a plant (not just a plantliving on a plant). Epibenthic organismsare those that live on the surface of thesediment, and include, in the broadestsense, motile organisms such as largegastropods and sea urchins, as well assessile forms, such as sponges and seaanemones or macroalgae. Infaunalorganisms are those that live buried inthe sediments, such as sedentarypolychaetes and bivalves, and relativelymobile infauna, such as irregular urchins.Organisms that are buried part-time, forshelter, such as penaeid shrimp or bluecrabs, or while waiting for prey, likeflounders, are considered epibenthic andnot infauna. Planktonic organisms are theminute plants and animals, such asdiatoms, dinoflagellates, and manycopepods that drift in the water column.They may show local movement, andespecially may migrate vertically, but arelargely at the mercy of water currents fortheir lateral movement. By comparison,nektonic organisms are highly mobileorganisms living in or above the plantcanopy, such as fishes and squids.

Another classification scheme, firstproposed by Kikuchi (1980), and slightlymodified by Zieman (1982), is based on themode of utilization of the seagrass bedsby the associated fauna. Thisclassification is based on whetherorganisms are: (1) permanent residents,(2) seasonal residents, (3) temporalmigrants, (4) transients, or (5) casualvisitors.

4.1 ALGAL ASSOCIATES

Epiphytic organisms are definedaccording to the usage of Harlin (1980)

The major sources of primary productionfor coastal and estuarine areas are: (1)macrophytes (seagrasses, macroalgae, salt

40

marsh plants, and mangroves), (2) benthicmicroalgae (benthic and epiphytic diatoms,dinoflagellates, filamentous green andbluegreen algae), and (3) phytoplankton.In estuarine and coastal regions therelative balance of standing crop andproductivity between the major groups ofprimary producers is a function of manyenvironmental variables, but the majordeterminants are water column nutrients,turbidity, and substrate. I n a r e a s o fhigh water-column nutrients, phytoplanktonand microalgal growth will dominate,because these small or single-cell algaerapidly respond to the increased nutrientsupply. Because benthic plants take upnutrients from the sediments via theirroots, these plants are less able toexploit increased nutrient levels in thewater column. The turbidity created byincreased algal growth, along withsuspended sediments, will causeattenuation of the light reaching thebottom of the water column and thusdecrease the light available to benthicplants for photosynthesis. Thus,increased nutrient levels_favor suspendedand epiphytic plants (both of which derivetheir nutrients from the water column) atthe expense of the benthic attached forms.Turbidity favors phytoplankton primarilysince they are capable of moving upward inthe water column to intercept the lightnecessary for photosynthesis. Sedimenttype is also important in determiningbenthic communities. - Soft sediments favorseagrasses and certain rhizophytic greenalgae, while rocky substrates favor thedevelopment of macroalgal communities.

While portions of the coastal region ofwest Florida are still miraculouslypristine, much of the area is heavilyurbanized or otherwise disturbed. Still,as late as 1968, Taylor and Salomanestimated that in Boca Ciega Bay totalproduction, dominated by macrophytes, wassix times the annual phytoplanktonproduction.

4.1.1 Phytoplankton

In the coastal and estuarine waters ofwest Florida, Steidinger (1973) identifiedfour phytoplankton assemblages:estuarine, estuarine-coastal, coastal-openGulf of Mexico and open gulf. Withinthese areas, diatoms generally dominate

the estuarine and inshore regions, whiledinoflagellates are more diverse andabundant in the open gulf and ingulf-influenced areas. The predominantorganisms are ubiquitous, cosmopolitanspecies that are coastal residents, butoccasional secondary abundance peaks areattributed to sporadic visitor species.Standing crop and productivity are higherin areas of terrestrial runoff or rivermouths, and are lowest offshore in theopen gulf, except in areas wheredivergence or upwelling make morenutrients available (Steidinger 1972,1973).

The phytoplankton of Tampa Bay aretypically dominated by nannoplankton (lessthan 20 pm), except for periodic blooms ofblue-green algae (Schizothrix)dinoflagellates (Gonyaulax, Gymnodiniiknelsonii and others). The dominantspecies in the bay is the diatom Skeleto-nema costatum. The red-tide organismPtychodiscus brevis (= Gymnodinium breve),a toxic coastal species. has invaded thebay 12 times between 1946 and 1982, domi-nating once for over three months(Steidinger and Gardiner 1985).

Johansson et al. (1985) estimated thatphytoplankton in Tampa Bay accounted for9l% of the submerged vegetative produc-tion. In deep areas of the bayphytoplankton production was estimated at340 8 C.m-2.yr-1; a maximum value of 620 gC.m- .yr-l was calculated from 14C data(Johansson et al. 1985). In Boca CiegaBay, Pomeroy (1960) estimated that phyto-plankton, benthic microflora, andThalassia production were of equal impor-tance in depths less than 2 m, whichincluded 75% of the bay. Phytoplanktonproduction dominated in deeper areas.

4.1.2 Benthic Algae

The coastal regions and estuaries ofwest Florida have a diverse benthic algalflora, occupying several differenthabitats. Although once regarded asdepauperate (Taylor 1954), the flora ofthe eastern gulf have been shown to bequite diverse in numerous subsequentstudies (summarized in Earle 1972; Dawes1974). In addition to cosmopolitan gulfand Caribbean species, the region also hasa pronounced seasonal peak of species with

41

a discontinuous Atlantic-northern gulf Mexico: west Florida waters exhibit lessdistribution (Earle 1972). Figure 17 variation in algal flora than the watersshows the relative richness and diversity of south Florida and northern Cuba but areof the algal flora of the region when more diverse in its algal composition thancompared to other areas of the Gulf of the northern Gulf of Mexico. Table 9

Taxonomlc Group Number of Specfes In Different Areas

ChlorophytaChrysophytaCryptophytaCyanophytaPhaeophytaRhodophytaTracheophytaXanthophyta

A B C D E F Total

85 42 45 43 97 1511

6 16 21 21 30 2:41 33 23 24 52 58120 121 86 42 171 270

6 5 4 6 6 61 1

1741

3182

349

Figure 17. Distribution and diversity of benthic marine plants in the Gulf of Mexico. Total is the actualnumber of species counted in areas A-F (after Earle 1972).

42

Table 9. Macroalgae of seagrass communities of the west Florida coast.

LocationTotalSpecies Cyanophyceae Chlorophyceae Phaeophyceae Rhodophyceae

Anclote Anchoragea 124 18 39 17 50

Apalachee Bayb 34 13 4 17

Seven SitesC 30 11 2 17

Crystal Riverd 106 19 24 63

Southwest Coaste 148 50 28 70

Table modified from Dawes (1987), with additional material. (a) Hamm and Humm(1976); (b) Zimmerman and Livingston (1976b); (c) Dawes (1985) Dominant speciesonly; (d) Steidinger and van Breedveld (1971); (e) Dawes et al. (1967). Manystations in this survey were offshore of developed seagrass beds.

lists the total number of macroalgal taxafrom several sites in Florida and showsthe distribution by division at each area.

Because of the combination of protectedestuaries on the central and southernportions of the Florida west coast and thegently sloping shelf and moderate waveclimate to the north of Tampa Bay, thewest coast offers an enormous area for thecolonization of either algae orseagrasses. The primary substratesavailable for algae in the region include:(1) rocky outcrops and hard bottom (2)soft sediments (3) seagrass leaves andmangrove roots and (4) the water column.Much of the shallow region north of TampaBay consists of rocky outcrops suitablefor algal attachment. Throughout thearea, oyster reefs, mangrove prop roots,and scattered rocks or shells offeradditional algal substrate, in additionto: human-made structures like pilings,bridge supports, and canal walls.

The only marine and estuarine algae ableto consistently utilize sediments assubstrate are the mat-forming algae andmembers of the order Caulerpales of thedivision Chlorophyta, which possesscreeping rhizoids that provide an anchorin sediments (Humm 1973; Dawes 1981).Among the most important genera areHalimeda, Penicillus, Caulerpa, and

Udotea, which are primary producers oforganic carbon. Halimeda and Penicillusalso deposit rigid skeletons of calciumcarbonate that become a major component ofthe sediments upon the death of the plant.

These algae do not have ability tostabilize the sediments as effectively asthe seagrasses, although they do buffercurrents to some degree, and by theirextremely rapid growth can accomodatechanges in shifting sediments.Historically, the main utility of theirrhizoidal holdfasts was considered to beserving as an anchor for the plant in thesubstrate, but Williams (1981) has shownthat they can take in nutrients throughtheir rhizoids and translocate thesethroughout the plant in a manner similarto higher plants.

In many tropical and subtropical seas,the calcareous green algae are the majorsource of sediments. The different generaproduce characteristic particles, withHalimeda tending to form sand-grain-sizedplates, while Penicillus producesfine-grained aragonitic mud. At currentgrowth rates, Penicillus alone couldaccount for all of the fine mud behind theFlorida reef tract and one third of thefine mud in northeastern Florida Bay(Stockman et al. 1967). In addition, thecombination of Rhipocephalus, Udotea, and

43

Acetabularia generates at least as muchmud as Penicillus in the same locations.

In the Bight of Abaco, Bahamas, Neumannand Land (19751 calculated that the arowthof Peniciilus,'Rhipocephalus, and Haiimedahas produced 1.5 to 3 times the amount ofmud and Halimeda sand now in the basin andthat in a typical Bahamian Bank lagoon,calcareous green algae alone produce moresediment than can be accomodated. Bach(1979) measured the rates of organic andinorganic production of calcareous greenalgae in Card Sound, south of Miami.Organic production was low in this lagoon,ranging from 8.6 to 38.4 g ash-free dryweight.m-2.yr-1, and 4.2 to 16.8 gCaC03.m-2.yr-1 for all the speciescombined.

In areas of western Florida with hardsubstrate, numerous species of attachedalgae are found. Amona the most commonbrown algae (Phaeophyta) are Dictyotadichotoma, Sargassum filipendula, S.pteropleuron, and Padina vickersiae(Zimmerman and Livingston 1976a; Dawes1987). The diversity of the red algae(Rhodophyta) is much greater throughoutthe area. Some of the more commonattached forms include Digenia simplex,Chondria littoralis, and several speciesof Gracilaria (Dawes 1987). The red algaeare the dominant forms in the drift algaeof western Florida waters, large mats oralgae that have become detached from theiranchorages. Rather than floatinq at thesurface-like Sargassum, they tend to rollalona on the bottom in clumas or lonacylindrical windrows, moved along by tidalcurrents or wind action. The dominantdrift alga is Laurencia, but members ofother genera, including Acanthophora,Hypnea, Spyridea, and Gracilaria, arecommon and may be locally abundant (Dawes1987).

Although information on the distribu-tion, standing stock, and seasonality ofmacroalgae on the west coast of Florida isbeginning to accumulate, studies on pro-ductivity on these plants are still sparse.In a study of seven seagrass communitieson the west coast of Florida, macroalgae,both attached and drifting, comprised from2% to 39% of the total plant standingstock (above ground biomass) (Dawes et al.1985; Dawes 1987). While Josselyn (1975)

estimated the production of Laurencia inCard Sound to average about 8.1 g dryweight.m-2.year-1, which was less than 1%of the production of Thalassia in thearea, algal production is undoubtedly muchhigher in areas where the macroalgae forma substantial portion of the totalbiomass.

The least studied components of thealgal flora continue to be the benthicmicroalgae. In studies of benthicproduction performed throughout theCaribbean, Bunt et al. (1972) found theproduction in Caribbean sediments toaverage 8.1 mg C.m-2.h-1 (range 2.5-13.8)using 14C uptake. By comparison, in theFlorida Keys sediment microbes fixed 0.3to 7.4 mg C.m-2.h-1. These values werefound to be equivalent to the productionin the water column. Lewis et al. (1985a)have suggested that within areas of excessnutrients and eutrophication, phytoplank-ton and benthic microalgae increase inabundance at the expense of seagrasses.

4.1.3 Epiphytic Algae

For many species of algae requiring afixed substrate for colonization andgrowth (both microalgae and those reachingrelatively large size), the seagrassesprovide that substrate in a habitat thatotherwise consists of inhospitable softsediments. Although unifying patterns arebeginning to emerge, the study ofepiphytes has suffered from what Harlin(1980) has described as the "bits andpieces" approach, with most studiesconsisting of either extended specieslists or suggestive but largelyobservational approaches (Dawes 1987).Literature is currently emerging thatfocuses on the important role thatseagrass epiphytes play as a trophic basein certain seagrass systems.

Humm (1964) compiled an annotated listof 113 species of algae found epiphytic onThalassia in south Florida. Of these onlya few were specific to seagrasses; mostwere also found on other plants or solidsubstrate. Later Ballantine and Humm(1975) reported 66 species of benthicalgae which were found to be epiphytic onthe seagrasses of the west coast ofFlorida. Table ID, shows the relativedistributions of algal epiphytes of sea-

44

Table 10. Algal epiphytes of the seagrasses of Florida (after Dawes 1987).

Site Total Cyanophyceae Chlorophyceae Phaeophyceae Rhodophyceae

Anclote Anchoragea 66 14 13 8 31(west coast)

Indian Riverb 41 4 10 10 17(east coast)

All FloridaC 113 10 15 19 69

aSeasonal collections (Ballantine and Humm 1975).

bSeasonal collections (Hall and Eiseman 1981).

'Non-seasonal (Humm 1964).

grasses at several locationsDawes (1987) further notes

in Florida.that fila-

mentous forms predominate as epiphytes,constituting 73% of the epiphytes from theIndian River and 58% of the epiphytes fromAnclote Estuary. Harlin (1980) compiled,from 27 published works, a species list ofthe microalgae, macroalgae, and animalsthat have been recorded as epiphytic onseagrasses. The algal lists are quitecomprehensive, but none of the reportslist the epiphytic invertebrates fromNorthwest Florida.

Harlin (1975) listed the factorsinfluencing distribution and abundance ofepiphytes as:

1. Physical substrate,2. Access to photic zone,3. A free ride through moving waters,4. Nutrient exchange with host, and5. Organic carbon source.

Providing a relatively stable (ifsomewhat swaying) substrate seems to bethe most fundamental role played by theseagrasses. The majority of the epiphyticspecies are sessile and need a surface forattachment. The turnover of the epiphyticcommunity is relatively rapid, since thelifetime of a single leaf is quitelimited. A typical Thalassia leaf has alifetime of 30 to 60 days. After a leafemerges, there is a period of time beforeepiphytic organisms appear. This may bedue to the relatively smooth surface or

the production of some antibiotic compoundby the leaf. On tropical seagrasses theheaviest coatings of epiphytes occur onlyafter the leaf has been colonized by thecoraline red algae, FosliellaMelobesia. The coral skeleton of the::algae may form a protective barrier aswell as a suitable roughened and adherentsurface.

Expressed in terms of population inter-actions, the relationship between epiphyteand seagrass host is basically that of anectoparasite. The relationship is bene-ficial to the epiphyte ectoparasite, butdetrimental to the seagrass host. Whilethe epiphytes enjoy the benefit of beingraised higher in the photic zone, theshading effect of the epiphytes has beenshown to be detrimental to the seagrasshosts (Orth and van Montfrans 1984),decreasing photosynthesis in Zostera by31% (Sand-Jensen 1977). In Australia,Bulthis and Woelkling (1983) found thatshading from accumulated epiphytes reducedby half the lifespan over which a leaf ofHeterozostera tasmanica showed positivenet photosynthesis. In areas of highepiphyte growth, the action of epiphytegrazers is extremely important in main-taining seagrass productivity, as well asthe longevity of the host seagrasses,without which the system would be non-existent (Orth and van Montfrans 1984).Epiphyte coverage is limited not only bythe activity of grazers, but, to a certain

45

extent, by the growth habit of the sea-grass plant, since individual leavessenesce and decay at such a rate that theyprovide a relatively temporary substrate.

In nutrient-poor waters, the epiphytescan benefit from the nutrients availableto the seagrasses in the sediments;several studies have shown that there canbe a transfer of nutrients from seagrassesto epiphytes. The upper surfaces of theleaves are subjected to much greater watermotion than the lower parts. One effectof the increased water movement is toreduce nutrient gradients produced bybiological uptake, thus increasingavailability of these nutrients tophotosynthetic organisms. In addition, amuch greater volume of water containingparticulate and dissolved nutrients isdelivered to suspension feeding animals.Harlin (1975) described the uptake of PO4orthophosphates translocated up the leavesof Zostera and Phyllospadix. Epiphyticblue-green algae have the capacity to fixmolecular nitrogen, but require phosphorusespecially in tropical waters. However,Goering and Parker (1972) showed thatsoluble nitrate fixed by epiphytes could,in return, be utilized by seagrasses.

The standing crop and productivity ofseagrass epiphytes and their resultantcontribution to the trophic base of thesystem are highly variable. In someareas, such as immediately behind a coralreef, there are few epiphytes and littlecontribution, but in other areas,especially those with high externalnutrient enrichment, the amount ofproduction is quite high. Jones (1968)estimated that in northern Biscayne Bay,epiphytes contributed from 25% to 33% ofthe community metabolism. Penhale (1977)found that epiphytes contributed 18% ofproductivity of Zostera meadows in NorthCarolina. The trophic structure of theseleaf communities can be quite complex andimportant in many areas, such as theshallow, turbid seagrass beds of theIndian River in Florida (Fry 1984) andparts of Redfish and Corpus Christi Baysin Texas (Kitting et al. 1984), and willbe discussed later. Much of the epiphyticmaterial, both plant and animal,ultimately becomes part of the litter anddetritus as the leaf senesces anddetaches.

4.2 INVERTEBRATES

The invertebrate fauna of seagrass bedscan at times be exceedingly rich anddifficult to characterize, except in verybroad terms, unless one is dealing with adefined area or is willing to produce anexhaustive, comprehensive species listsince hundreds of species can potentiallybe represented within a small area. Thissame fauna can be highly variable, withdramatic changes occurring in the fauna1composition and density within relativelysmall changes of time or distance (Brook1978).

From south to north along the westerncoast of Florida, there is a change in theinvertebrate fauna of the seagrass bedsand associated habitats, beginning as aCaribbean-West Indian fauna at the southand emerging as a predominately temperatefauna in the northern gulf. Collard andD'Asaro (1973) noted that the southerlyfauna with West Indian affinities changesto one with Carolinian affinities in thenorth. They tentatively divide the faunasat the vicinity of Cedar Key but statethat the change is gradual and that thereare no clear-cut fauna1 provinceboundaries in the eastern Gulf of Mexico.

The characteristic species of seagrassbeds and associated communities from thewest coast of Florida have been describedby Collard and D'Asaro (1973) and theseassociations are listed for the northern(Carolinian) fauna (Figure 18) and for themore southerly (West Indian) fauna (Figure19). Some of the cosmopolitan fauna thatare found in both regions are the seaurchin Lytechinus variegatus; the bivalvesArgopecten irradians, Modiolus modiolus,and Cardita floridana; and the gastropodsf a s c i a t aTegula and Bittium varium. Inthe classification of Collard and D'Asaro,the West Indian fauna coincide with theinvertebrate fauna described in detail forthe seagrass communities of south Floridaby Zieman (1982).

In Apalachee Bay, Hooks et al. (1976)found that 6 of the 10 most abundant"trawlable" species (=epibenthic and largeepiphytic fauna) in the area wereseagrass-associated fauna. Some of themost common organisms found in the baywere the caridean shrimps, especially

46

BAY AND SOUND COMMUNITIESFORESHORE

MLtiST

TROUGH

GRASS iBureatella leachi (cj

BAR OFFSHORE

. .: : ‘Macoma constricta (vc) .:

” :. ” .. ‘: :‘::Diplodonta punctata (c)

Figure 18. Representative temperate (Carolinean) invertebrate communities (after Collard and D’Asaro1973).

Palaemonetes pugio, Palaemonetesintermedius, Periclimenes longicaudatus,Palaemon floridanus, Tozeuma carolinense,and HiA l s o a b u n d a n tppolyte pleuracantha.were the scallop irradians; thehermit crab Pagurusbonairensi>; theechinoderms Lytechinus variegatus andEchinaster serpentarius; and the majidcrabs Libinia dubia, Metoporhaphiscalcerata. and Podochela riisei. Workinain the same area, Dugan and Livingston(1982) found similar species associations.

In Tampa Bay, Santos and Simon (1974)found that the Thalassia zone supportedthe laraest number of infaunal polvchaetesof any of the sampled habitats of the bay,although only three of the nine mostabundant species showed their highestdensities in this zone. In grassbedsoffshore from the mouth of the EconfinaRiver in Apalachee Bay, polychaetes madeup 35% of macrofaunal numbers, reachingmaximum densities of 2,947 polychaetes per

square meter (Stoner 1980b). The relativeabundances of epifaunal species weredirectly related to macrophyte density;however, densities of burrowingpolychaetes varied inversely withmacrophyte density. In this studyamphipods made up 47% of the macrofaunaand reached densities of 1,578 m-* (Stoner1980b). Normally, small crustaceans suchas amphipods and isopods will benumerically in great abundance; however,the larger penaeid and caridean shrimpoften represent a larger biomass withinthe bed. Data from Brook (1977) fora Card Sound Thalassia grass bed showsthat amphipods and caridean shrimprepresent respectively 5.8% and 23.3% ofestimated biomass of principal taxacollected and 12.4% and 50.3% ofcrustacean biomass.

The data of Collard and D'Asaro suggestthat there is a greater proportion ofemergent organisms (those living at or

47

FORESHORE

MYST

Jardisomi guanhumi

Ocypo$e albicans

BAY AND SOUND COMMUNITIESTROUGH BAR

Haminoea antillarum [vc)H. elegans (c)Argopecten irradians ic)Cardita floridana (vc)!Thor floridanus (c) iTozeuma carolinensisi(c)Pagurus annulipes (VC)Fasciolaria tulipa (c)Echinaster sentus (c) /Lytechinus variegatus’ (vc)Mithrax spinosissimus (c)Holothuria floridana (c)Ophioderma brevispinum (vc)Tegula fasciata (c) ;_

OFFSHORE

: ,,... :;.... ..: ::.‘..~::;. ‘, -:,...’ .:< :

. ..*.

‘.! .‘_‘..,‘. \ . . . . ,.: .:..: ..’ .;c. .;...:_ .. ...,,.. . . ‘.‘.i . . ...,’ ,pkna caTnea cc) :- 'c , .;, ::,;:..‘; .,. .: :Lutota senegan

2. : .: :.,:.: . . . :.: :: .., ::.:, . . . . I : . . . . . .*.; .., ...,’ . ..,

i;:::,,: ,.,,‘,,, 1. _..:.. :.:..,::. ,‘,.,.,.,.: :.: . ., . . ,,,’ ;,., . ..:.,:.,‘p::.:‘,,,. ’ .. ” 'Alpheus hetero chaelis (vc

‘..‘...’ “.:;.‘,,.‘,‘.. . . . . ‘.‘.....,‘....“,:‘,..,.,. ‘..‘., . . . .,’ . ..’ i,:: :,. :, Codakia orbiculata (c) :,‘..’ . :’ .:’ :’

:, ,: ,..., ‘..‘..?.,.. :::::::, ;.;,:,._ ,,.,,, .,:

..“... . .,.. .,..,:,._ .,: :.., ‘:_..

‘.,...’ .‘. . .. ‘,‘,‘;‘. : ‘..,‘.. Chione cmce,lata cvC. ::I ‘: . . . :::: 1. 1. Tdllina alternal ta (vc) ._‘_

,_::.: : . .,. . ,,:::. ..; :.. ‘,‘. ‘. ‘.. . . . ; .\ . Cistenides gouldii (c) I:,:::::i+ .:_.: ,.<: ,..’ . . . . . ..r. ..: :, : ,.:::.,, I;,: : .:.:::..: 1. ::,: ‘,I. . .., .:.;.:., :,.‘. : 1 .;: :::I I:i‘Anomalocardia cuneimeris (vi) ‘li ., :,.::.. . ‘, ,: .

. ..” _.,.. ‘..:i:::. ..,:;I . . : ‘1’ ..,.: :..,. :.. ,.: : :: ..,i:: ‘. : y’. ,.. .: .:. .,,.: 1.1. i. .,

.;. . . :. . . . . . . . . ‘..., :.,.:“Tellina promera (vc) .: ,:‘,.,‘-;m~.: .:.:,::::I! .“:.‘. _’ .<I: ::...f’:: :.‘:‘.--,: :::;f,, . ..’ .:. . . . . .,I .:,:.: i : -.: .:_. ‘:- ,:

.:.j::’ : : . . . . . . _.. . . . . . ..,: . . . . . . . . . . . ;.. . . . 1.. “.::.. .: ,_:’ : ,:,:: . . :y.:. :.. ::: . :,. . . ‘, :. . _y: T. similis (v”‘,.,:‘,,:I’:,:_ ; .:,;.,: ,:.: .:,:‘:.:::::. ; ‘,‘,. ,,‘.:‘.... . .‘.‘I. ‘., ,.

‘I;- pugilator (vc) Turbo castanous (c) f._~_~~~~__~~“~~Chhh~~ Modulus modulus (c) i~A*-hhhhhhhh/

,l_lrl IlllALlA.IY \.-, Cerithium muscarum (c)._~__ _________

-.::_;; ::?tdi Ophiolephis elegans (vc) C. Boridanum (C)i Nmnmnne rc=x~nn Irl

i Limulus poly,,hpi,,c (,.\Bittium varium (vc) i

Figure 19. Representative tropical (West Indian) invertebrate communities (after Collard and D’Asaro 1973).

above the sediment surface) than infaunalorganisms (those living in the sediment)in the seagrass beds of the southern partof the west Florida coast, changing to alesser proportion of dominant emergentforms in the north. In addition, theysuggest that there are more abundantfauna, both emergent and infaunal, in thesurrounding sand and muddy areas in theareas of the Carolinian fauna1 provincesthan in the West Indian provinces.

4.3 FISHES

Seagrass meadows are often populated bydiverse and abundant fish faunas. Theseagrasses and their attendant epiphyticand benthic fauna and flora provideshelter and food to the fishes in severalways. The grass canopy provides shelterfor juvenile fishes and for small

permanent residents. These also can feedon the abundant invertebrate fauna of theseagrass meadows, on the microalgae, onthe living seagrasses themselves, or onseagrass detritus. In addition, becauseof the abundance of smaller fishes andlarge invertebrate predators, such as bluecrabs and penaeid shrimps, larger fishesin pursuit of prey organisms transit themeadows, using them as feeding grounds.Numerous surveys have documented the fishfaunas of a variety of areas along thewest coast of Florida. These have mostrecently been reviewed and synthesized byComp (1985).

Fishes that are permanent residents inthe seagrass beds are typically small,less mobile, more cryptic species thatspend their entire lives there. Thesespecies are normally of little or nodirect commercial value but are often

48

characteristic organisms of the seagrasshabitat and may be highly important asforage for larger fishes, including thoseof commercial and sportfishing importance.The families and species comprising thiscategory for seagrass meadows on theFlorida west coast are nearly identical tothose in south Florida (Zieman 1982).Members of families Syngnathidae,Gobiidae, and Clinidae are characteristicof this group. Pipefishes and seahorses,including Syngnathus scovelli S.floridae, Micrognathus cr;niger,Hippocampus zosterae and H. erectus,abound in the western Florlrda seagrassmeadows. The gobies and clinids showstrong affinities with the south Floridaspecies, and are represented commonly byGobiosoma robustum, Microgobius gulosus,and Paraclinus fasciatus. Alsocharacteristic of the more crypticgrassbed fauna are the predators that-iurkwithin the beds or at their edge waitingfor mobile prey. Representative of theseare the toadfish, Opsanus beta, thebatfish Ogcocephalus radiatus, and thelizardfish, Synodus foetens (Mountain1972; Springer and Woodburn 1960). Themost common stinqray in the northeastinshore gulf is Dasyatis sabina (Mountain1972).

A group of resident fishes that arerarely caught with conventional methodsare the eels. In St. Croix seagrass beds,Robblee and Zieman (1984) were able toobtain repeatable quantitative samplesusing an encircling net and rotenone.Capitalizing on a "natural experiment,"Springer and Woodburn (1960) observedlarge numbers of the ophicthid eel,Ophichthus gomesi, following a severe redtide. Mountain (1972) noted that offCrystal River the most common eel in trawlsamples was the blackedge moray,Gymnothorax nigromarginatus, a commonnocturnal forager in seagrass beds.

Seasonal resident fishes in thegrassbeds are those which spend theirjuvenile or sub-adult stages or theirspawning season there. These are abundantfishes that are usually highly visible andare characteristic of grassbed fauna.They include the Sciaenidae, Sparidae,Pomadasyidae, Lutjanidae, and Gerreidae.Some of these species are also found inresidence throughout the year.

Comp (1985) found two main spawningtimes in Tampa Bay. The larger one occursin the spring and early summer, whichenables the juvenile fishes to takeadvantage of the high summer primaryproduction. The second, smaller spawningoccurs in the late summer and early fallmonths (Comp 1985).

The most abundant fishes in the seagrassbeds of Apalachee Bay are listed in Table11. The most abundant is the pinfish,r h o m b o i d e s ,Lagodon which numerically canoften exceed all other fishes combined inabundance (Ryan and Livingston 1980). Thepinfish was also observed to be one of themost common fishes in Tampa Bay (Springerand Woodburn 1960; Comp 1985) and theseagrass beds off Crystal River (Mountain1972). McNulty et al. (1974) found thepinfish to be the most common fish in acomposite list from five estuarine areasfrom St. Marks to Chokoloskee. Themost common, the sciaenids, wereLeiostomus xanthurus, the spot, andBairdiella chrysoura, the silver perch.In general, the fishes abundant in theseagrass beds of the Florida west coastare similar to those of south Florida,especially the fauna found in the seagrassbeds of Florida Bay (Zieman 1982). Table12 gives a comparison of the relative

Table 11. Most abundant fish of Apalachee Bay (afterLivingston 1984a).

Species Common name

r h o m b o i d e sLagodonLeiostomus xanthurusBairdiella chrysuraMonacanthus ciliatusDiplodus holbrookiSygnathus floridaeOrthopristis chrysopEucinostomous gulaCentropomus melana

tera

PinfishspotSilver perchFringed filefishSpottail pinfishDisky pipefishPigfishSilver jennyGulf black seabass

Monacanthus hispidus Planeheadfilefish

Eucinostomus argentius Spotfin mojarraParaclinus fasciatus Banded blennySygnathus scovelli Gulf pipefishAnchoa mitchelli Bay anchovy

49

Table 12. Relative abundance of fish families in seagrass meadows (Pollard 1984.

State number 7 8 9 10 11 12 13 14Region Gulf of Mexico - Florida area CaribbeanLocality N.W. Florida Texas N.W. Florida C.W. Florida S.W. Florida Texas S.E. Florid PanamaLatitude 29'N 28'N 30°N 28'N 26'N 28'N 26ON 9ON

Main seagrass genusReference

Halodule ThalassiaCarr and Hellier Livingston Springer and Weinstein Hoese Springer WeinsteinAdams (1962) (1975) Woodburn and Heck and and and Heck(1973) (1960) (1979) Jones McErlean (1979)

(1963) (1962)

Fish Family Rank

Syngnathidae 1Gobiidae 2Monacanthidae 3Sparidae 4Labridae 5Gerreidae 6Scorpaenidae 7Sciaenidae 8Tetraodontidae 9Blenniidae 10Clupeidae 11Ambassidae 12Apogonidae 13Engraulidae 14Bothidae 15Mugilidae 16Teraponidae 17Cyprinodontidae 18Muliidae 19Haemulidae 20Clinidae 21Centracanthidae 22Searidae 23Serranidae 24Diodontidae 25Gasterosteidae 26Lutjanidae 27

+14 +-_ __1 +

__ -_6 +

2 +13 +9 __

8 +

__ _-5 +

__ +__ +

__ +

3 +__ __

__ ____ _-

-_ __

4 28 43 391 5

-_ __

7 930 -_

2 115 1612 1425 7_- __30 __

19 616 2430 8__ __

25 3__ __

6 2410 ___- _-_- __5 __

11 24_- _-

22 16

(Continued)

41485

__3

11119-___

2214

__-_

2

__

1379

-_

6

++

__+

_-+

__+

_--__-__-_

+++

_-+

_-+

_-_____--__-_-

7159

:;2

213719__

11

_-

11025

5374

12_-

63726

8

15104

131438

175

3118-_222616__-_

116

31-_

27

12-_

1

m .. .-- __. - _- _^ _

Table 12. (Continued).

State number 7 8 9 10 11 12 13Region

14Gulf of Mexico - Florida area

LocalityCaribbean

LatitudeN.W. Florida Texas N.W. Florida C.W. Florida S.W. Florida Texas S.E. Florida Panama29'N 28'N 30°N 28ON 26ON 28'N 26'N 9='N

Main seagrass genus Halodule ThalassiaReference Carr and Hellier Livingston Springer and Weinstein Hoese Springer Weinstein -

Adams (1962) (1975) Woodburn and Heck and and and Heck(1973) (1960) (1979) Jones McErlean (1979)

(1963) (1962)

Fish Family Rank

Odacidae 28Kyphosadae 29Eleotridae 30Congiopodidae 31Belonidae 32Batrachoididae 33Cottidae 34

I? Atherinidae 35Sillaginidae 36Arripidae 37Aulorhynchidae 38Carangidae 39Platycephalidae 40Solcidae 41Plotosidae 42Anguillidae 43Gobiesocidae 44Hemiramphidae 45Callionymidae 46Lethrinidae 47Pomacentridae 48Siganidae 49Gadidae 50Scorpididae 51Cynoglossidae 52Pleuronectidae 53Acanthuridae 54Muraenidae 55

__ __-_ ____ __-_ -_

______

++

__+

__ __ ____1424__

3__

11 + __ 199 24 10__ __

__ __

407 + __ 11 ____ ____ ____ -_

____ -_ __

2212 30__41____

223341__

41__

36

4 __ 22 10__ __

17__

15 __ 24__

20 10____

__ __-_ -___ __

_- -_ _- ______ 24

__ 24

______

10 + -_______

__ ____ ____ -___ ____ -___ ____ __-_ ___- -___ __

__ ____ ____ __

36

14 24 ____

31__

20__

20 24 36__

2034

__ ____ ____ 12

__-___

(Continued)

Table 12. (Concluded).

State number 7 8 9 10 11Region

12 13 14Gulf of Mexico - Florida area

LocalityCaribbean

LatitudeN.W. Florida Texas N.W. Florida C.W. Florida S.W. Florida Texas S.E. Florida Panama29'N 28'N 30°N 28'N 26ON 28'N 26ON 9'N

Main seagrass genus Halodule ThalassiaReference Carr and Hellier Livingston Springer and Weinstein

Adams (1962) (1975)Hoese Springer Weinstein

Woodburn and Heck and and(1973)

and Heck(1960) (1979) J o n e s McErlean (1979)

(1963) (1962)

Fish Family Rank

Chaetodontidae 56 -- __ __ -_ __ __ __Aulostomidae

957 -- __ -_ -- -_ __ __ 31

No. fish speciesNo. fish familiesOther seagrass

genera present

21 31 57 93 49 19 106 10615 20 36 47 25 13 48 45

Ruppia Ruppia Syringodium Halodule ? Halodule HaloduleSyringodium

Syringodium

VIN Depth range (m) 1 1 2 ? ? 1 2 1 2

Main ~011. method Seine net Drop Otter trawl Various Otter trawl Drop net Seine net Otternet trawl

"+"indicates presence."--"indicates none found.

abundance of fish families in seagrassmeadows in the region.

In addition to the fishes readily caughtin trawl surveys, there are numerousseasonal residents and a few permanentresidents, that are highly mobile and arequite abundant, but are not easily sampledwith this gear. Such fishes include theAtlantic spadefish, Chaetodipterus faber;the sheepshead, Archosargusprobatocephalus; the red drum, Sciaenopsocellatus; and the mullets Mugil cephalus,M. trichodon. and M. curema (Sorinaer andRoodburn 196b; Mo&ain72): M&y ofthe fishes in this category are those withsignificant commercial or sportfisheriesimportance (Thayer et al. 1978a).

Notable by their absence in northwestFlorida grassbeds are the large numbers ofjuvenile snappers and grunts that use theseagrass meadows of south Florida asnurseries, move to the offshore reefs asadults, and commonly return to theseagrass beds at night to feed (Starck andSchroder 1970). The white grunt Haemulonplumieri seems to be the only lutjanidfound through out the region and the graysnapper, Lutjanus griseus has the widestdistribution of the serranids (Springerand Woodburn 1960; Mountain 1972; Ryan andLivingston 1980). The spotted sea trout,Cynoscion nebulosus, is a major gamefishduring much of the year over seagrassbeds, often found following large schoolsof foraging mullet.

The large roaming predators, or'occasional migrants" aclassification scheme of Kikuck: (196EFeare not normally present, visiting thigrass beds to forage only infrequently and(if You are sportsfisherman)unpredictably. On the" Florida west coasttwo of the most sought afte;representatives of this qroup are thetarpon, Megalops atlanticus, and the kingmackerel, Scomberomorus cavalla. Suchtransient predatory species represent onlya small proportion of the biomass presentbut may be quite important in determiningfish community structure.

4.4 REPTILES

The only reptiles that are commonlyassociated with seagrass meadows are thesea turtles, of which there are several inthe eastern Gulf of Mexico. The onlyherbivorous sea turtle is the green seaturtle, Chelonia mydas. Throughout itsrange, the primary food of the greenturtles is sea grasses and the preferredfood is Thalassia (hence its common name,turtle grass). Although not a seagrassfeeder, the Atlantic ridley, Lepidochelyskempi, is often caught in commercial netsset for green turtles in seagrass areas onthe upper Florida west coast (Carr andCaldwell 1956).

In pre-Columbian times, green turtleswere abundant throughout the Gulf andCaribbean, but from very early on werehunted extensively for their succulentmeat and calipee (fat), the ingredientthat gives turtle soup its unique anddelicious flavor. Concern over thereduced populations of green turtles datesback to the previous century (Munroe1896). Although limited nesting occurs onthe small beaches of south Florida, theregion has almost certainly been primarilya feeding rather than nesting site. Carrand Caldwell (1956) noted that the greenturtle populations of Florida werecomposed almost entirely of nonbreedingjuveniles. The former turtle fishery onthe Florida west coast was a seasonal onethat began in April and extended until thefirst cold front of the fall. Mostscientists believed that the turtles leftthe area in mass migrations in the fall,but some local fisherman insisted that theturtles would "bury up" in the mud bottomsand in holes on mud flats and remain therethroughout the winter (Carr and Caldwell1956). Although turtling was carried outto some degree throughout the west coastof Florida from the Florida Keys to CapeSan Blas, the greatest activity was in thegrass beds near the mouths of theWithlacoochee and Crystal Rivers, an areaof superior turtle habitat (Carr andCaldwell 1956).

4.5 BIRDS

Shallow seagrass meadows offer feedingand resting areas for many species of

53

birds, but in most cases the exactrelationship between the birds andseagrass meadows is unknown. Theembayments of the west coast of Floridaare one of the most important areas formany bird species, which either winter inthese sheltered bays or use the areas asresting and feeding sites duringmigration. The ecology of wading birdsand their feeding behavior have beenreviewed by Kushlan (1976, 1978). Odum etal. (1982) reviewed the avifauna of themangrove regions of southern Florida,while Woolfenden and Schreiber (1973) gavean extensive review of the birds of marineand brackish-water habitats of the westerncoast of Florida.

Table 13 lists 81 species of birds thatutilize saline habitats in the easternGulf of Mexico. This information, basedon Christmas bird-count data, shows atleast one broad generalization of habitatusage. Nearly all of the 81 specieslisted occur throughout the coastal watersof western Florida, but there is avariation in the relative abundance, whichmay be related to habitat usage. In southFlorida, with its high concentration ofshallow seagrass flats, the most abundantbirds are the wading birds that feed inshallow water or on seagrass or mudflats,especially the Ardeidae (herons andegrets) and the Scolopacidae (sandpipers).In contrast, throughout the peninsular andpanhandle bays, the most abundant groupswere the Anatidae, containing geese andducks; the Gaviidae, including the commonloon; and the Rallidae, including theAmerican coot. Unlike the wading birds,these birds tend to rest on the open waterof the bays, commonly in rafts of dozensto hundreds or even thousands ofindividuals. Many of these species feedin the bays, diving to capture fishes orinvertebrates or to forage for grasses,plant tubers, or rhizomes. The mostcommon waterfowl is the lesser scaup,Ay;;y;,affinia, which is most abundant in

saltwater habitats, oftenoccurring in flocks of over 10,000individuals. Its primary food is benthicinvertebrates, along with some fish andplant material (Woolfenden and Schreiber(1973). Another common swimming bird isthe double-crested cormorant,Phalacrocorax auritus, which pursues fishin the water column. Cormorants may be

found wherever the water is sufficientlydeep for them to swim and clear enough forthem to spot their prey.

The groups of birds described above usetwo of the dominant feeding modes of themarine avifauna. A third group hunts byflying some distance above the water untilprey is spotted and then plummeting fromthe air to seize it. Ospreys, Pandionhaliaetus, and bald eagles, Haliaeetusleucocephalus, feed in a similar manner byseizing prey on the surface of the waterwith their claws, while the brown pelican,Pelicanus occidentalis, plunges from somedistance in the air to catch fishes in itspouch. For these birds, the seagrassmeadows provide an abundant source of foodby concentrating their quarry more thanmuch of the surrounding habitat. Largerbirds such as these require greatquantities of food for themselves andtheir young, and are dependent on thelocal environment not only for protectednesting sites, but for a healthyforage-fish population. Woolfenden andShreiber (1973) stated that a juvenilebrown pelican requires approximately 120lb of fish to fledge successfully.

4.6 MAMMALS

On the west coast of Florida, Caldwelland Caldwell (1973) reported that 27species of marine mammals have beenobserved or reported stranded on beaches.Ode11 (1979) reported the same number insouth Florida. Many of the sightings arerare or of dubious value; only two marinemammals are commonly found in the shallowcoastal waters of west Florida: themanatee, Trichechus manatus; and thebottlenose dolphin, Tursiops truncatus. Athird species, the spotted dolphin,Stenella plagiodon, is common offshore,and on occasion will venture in closeenough to be observed from shore.Numerous sightings of a pinniped, theCalifornia sea lion, Zalophuscalifornianus, were reported (Gunter1968). however. Caldwell and Caldwell(1973) question'that the feral sea lionshave established a breeding population.

The bottlenose dolphin is, by aconsiderable margin, the most commonmarine mammal in coastal Florida waters,

54

Table 13. Number of individuals per 10 party hours based on Christmas Bird Count Data, 1957-71, from 17selected localities grouped in four regions, and for all counts combined (t = trace, less than 0.5 individuals; linesseparate the families) (from Woolfenden and Schreiber 1973).

Common name

Common Loon

Pan- Penin- CootScientific name handle sula Bay Keys Totala

Gavia immer 12 1 t t 3- -

Horned Grebe Podiceps auritus 17 1 3 2 5

Wilson Petrel Oceanites oceanicus 0 0 0 0 0

White Pelican Pelecanus erythrorhynchos t 3 142 2 25Brown Pelican Pelecanus occidentalis t 52 37 54 39

Gannet Morus bassanus t 0 0 t t

Double-crested Cormorant Phalacrocorax auritus 40 63 98 121 71

Magnificent Frigatebird magnificensFregata 0 1 t 6 1

Great White HeronGreat Blue HeronGreen HeronLittle Blue HeronReddish EgretCommon EgretSnowy EgretLouisiana Heron

Ardea occidentalis-_Ardea t-lerodiasButori;ies virescens-Florid; I caerulea_ -DichronianCasmerc,dius albusLeucopt zthulaHydran;lssa tricolor

lassa rufescens

Black-crowned Night Heron Nycticorax nycticoraxYellow-crowned Night HeronNyctanassa violacea

05t50

13241t

t81

14

1;14714

1926 613 254 142 3

129 9132 740 147 t3 3

12 5103

191

32291323

Wood Stork Mycteria americana t 5 65 1 13

White IbisRoseate Spoonbill

Eudocimus albusAjaia ajaja

3 34 267 11 620 t 19 8 4

Canada Goose Branta canadensis 114Mallard Anas platyrhynchos 26Black Duck Anas rubripes 4Mottled Duck Anas fulvigula 0Gadwall Anas strepera 9Pintail Anas acuta 28Green-winged Teal Anas carolinensis 4American Widgeon Mareca americana 49Shoveler c l y p e a t aSpatula 3Redhead Aythya americana 88Canvasback v a l i s i n e r i aAythya 2Lesser Scaup a f f i n i sAythya 203Common Goldeneye Bucephala clangula 9Bufflehead Bucephala albeola 26Ruddy Duck Oxyura jamaicensis 3Red-breasted Merganser Mergus serrator 26

t1

518371tt

185ttt

27

0

i7

17;814544t

17:.0t4330

000

it11

0"0

:00

33

256123

3815218

191

163258

28

(Continued)

55

Table 13. (Continued).

Common name Scientific namePan- Penin- Coothandle sula Bay Keys Totala

Bald Eagle Haliaeetus leucocephalus t 1 2 1 1

Osprey Pandion haliaetus t 1 7 5 2

Clapper RailSoraAmerican Coot

1 t 1 1 1

15: 32 t 24: t 3 8;

American Oystercatcher Haematopus palliatus t

Semipalmated PloverPiping PloverSnowy PloverWilson PloverBlack-bellied Plover

Ruddy TurnstoneWilletGreater YellowlegsLesser YellowlegsWhite-rumped SandpiperLeast SandpiperDunlinShort-billed DowitcherSemipalmated SandpiperWestern SandpiperMarbled GodwitSanderling

semipalmatusmelodusalexandrinuswilsoniasquatarola

Arenaria interpres 2Catoptrophorus semipalmatus 11Totanus melanoleucus 1Totanus flavipesErolia fusiocollis :Erolia minutilla 2Erolia alpina 59

8 6 2411 45 6 1:1 8 5 3

26 1 4 130 0 06 115 35 2:

49 211 37 7611 54 134 3318 153 54 436 62 21 591 7 t 2

26 1 12 17

51211

10

7 10 19 8114

13

American Avocet Recurvirostra americana t tBlack-necked Stilt

8 tlHimantopus mexicanus 0 t t t t

Parasitic Jaeger Stercorarius parasiticus t 0 t t t

Herring Gull Larus argentatus 39 35Ring-billed Gull

3 15 28Larus delawarensis 76 316 38 74 183

Laughing Gull Larus atricilla 15 104 92 132 86Bonaparte Gull Larus Philadelphia 19 1Gull-billed Tern

t 15Gelochelidon nilotica t 1 1

Forster Ternt

Sterna forsteri 10 8 5Roseate Tern

; 8Sterna dougallii 0 t 1t

Sooty Tern Sterna fuscasa 0 0Least Tern

0" t 0Sterna albifrons t t 0 0

Royal Tern Thalasseus maximus 3 29Sandwich Tern

12 56 2:Thalasseus sandvicensis t 5 14 3

Caspian TernBlack Tern

Hydroprongne caspia 1 7 2 2Brown Noddy Chlidonias niger 0" 0A n o u s 0 0 0

stolidus 0 0 0 0 0

(Continued)

56

Table 13. (Concluded).

Pan- Penin- CootCommon name Scientific name handle sula Bay Keys Totala

Black Skimmer Rynchops nigra 3 41 161 28 50

Mangrove Cuckoo Coccyzus minor 0 t t t t

Seaside Sparrow Ammospiza maritima 2 t t 0 t

aTotal represents the average of all birds

although accurate censuses of theirabundance and distribution are rare. Inthe Everglades Park region of southFlorida, Ode11 (1976) found that 36% ofthe animals seen were in open Gulf ofMexico waters, 33% were in Whitewater Bay,20% were in inland waters and 11% wereseen in Florida Bay. The relatively lownumbers in Florida Bay were presumed to bedue to extremely shallow waters whichwould inhibit the movement of this largemammal. In a later survey, Irvine et al.(1982) found 700 individuals in 146 herdsin the Gulf of Mexico, 491 individuals in185 herds in bays, and 192 individuals in100 herds in marsh and river habitats ofwestern peninsular Florida. Bottlenosedolphin are opportunistic feeders,subsisting primarily on fish, squid, andbenthic invertebrates (Caldwell andCaldwell 1973). Their diets are not wellknown, but they are frequently observedpursuing schools of mullet.

The Caribbean manatee or sea cow,Trichechus manatus, is primarily tropicalin distribution, but its range formerlyextended across the Gulf of Mexico. On thewest coast of Florida, it is found in theshallow coastal seagrass meadows or in thecoastal rivers. Although its numbers havegreatly declined (in recent years) causingit to be placed on the Federal EndangeredSpecies List, recent large increases inpopulations along the southern Big Bendcoast of Florida have been reported(Powell and Rathbun 1984). This coastlineprovides abundant summer feeding grounds

counted in all areas combined.

in the coastal grassbeds and wintershelter in the spring-fed rivers of theregion, notably the Crystal and HomosassaRivers, which during the winter are warmerthan the coastal waters (Powell andRathbun 1984). Recently heated effluentsof large power plants, especially nuclearplants with their lower thermal efficiencyand greatly increased heat output, haveprovided additional refuges.

Normally, manatees forage singly, orwith a mother and calf pair, in theshallow estuarine grassbeds during thewarmer months. The major summer feedinggrounds are the estuaries and offshoregrass beds of the Crystal, Homosassa,Suwanee, Withlacoochee, and Chasshowitzkarivers (Powell and Rathbun 1984). Hartman(1969) reported that they spend a quarterof each day feeding, and will consume atleast 10% of their body weight a day invegetation, a significant amount ofseagrass considering adults weigh up to500 kg.

A survey of western peninsular Floridacounted a total of 554 manatees, with thehighest percentage sighted in the shallow,brackish waters of Collier and Monroecounties in extreme south and southwestFlorida (Irvine et al. 1982). In anearlier study of the Everglades and thesouth Florida region, Ode11 (1976) found atotal of 302 herds with 772 individuals;46% were sighted within Whitewater Bay,20% in the Gulf of Mexico, 23% in inlandwaters, and only I% in Florida Bay.

57

CHAPTER 5. STRUCTURAL AND FUNCTIONAL RELATIONSHIPS IN SEAGRASS SYSTEMS

The importance of seagrasses to theproductivity of shallow coastal waters iswell-recognized: they provide shelter andserve as nursery and feeding grounds fordiverse assemblages of organisms. Thevariety observed in community structure inseagrass beds has stimulated efforts toidentify the functionalwithin the beds,

relationshipsand thus provide a

framework for understanding theinteractions and pathways common to thesesystems.

5.1 THE RELATIONSHIP OF STRUCTURE,SHELTER, AND PREDATION

Seagrasses, with leaf canopies extendinginto the water column and rhizome systemspenetrating the sediment, present astructurally complex habitat where calmwater, a stable substrate, and anabundance of detrital and microalgal foodsupport dense populations of motile andsessile organisms. The increasedabundance of infaunal and epifaunalorganisms which find shelter andprotection from predation within thegrassbeds promotes, in turn, the value ofseagrass habitats as feeding grounds forthe predators.

While the fauna1 richness of seagrassbeds was recognized in early studies, morerecent works have begun to identifyspecifically the interactions amongcomponent plant and animal species and todefine their functional relationships.

5.1.1 Fauna1 Abundance and Structure

Early ecological surveys of Floridacoastal waters included observations ofincreased densities of fishes andinvertebrates within seagrass bedscompared to adjacent habitats. Later

studies quantified these differences infauna1 abundance (Roessler et al. 1974;Yokel 1975a, 1975b; Thorhaug and Roessler1977; Weinstein et al. 1977). The concisestudy of Yokel (1975b) reports thefindings of this phase of studies.Results from trawls showed that in theRookery Bay Sanctuary, 3.5 times as manyfishes were captured in seaqrass as inbare sand and shell substrates (FigureZO), and the standing crop of crustaceans(estimated from trawls) was 3.9 timeslarger in mixed seagrass and algal flatsthan on nearby unvegetated bottoms.

The amount of literature demonstratingthe increased abundance of organisms inseagrass communities . becomingextensive. Table 14, from"Virnstein eta1.(1983) summarizes much of the pertinentliterature. Numerous studies ranging inarea from Florida to Japan to Belize showthat in nearly all cases, the ratio of

m F\sh

( Invertebrates

H E A V Y T H I N S A N D / M U D /SEAGRASS SEAGRASS S H E L L S A N D /( Halodule a 1 Holodule 1 S H E L LThalassiq)

Figure 20. Comparison of fauna1 abundance betweenseagrass beds and adjacent habitats (after Yokel1975a).

58

Table 14. Comparison of seagrass: sand fauna1 density ratio (G:S) with other studies. Abundances are per m2 except those listed in parentheses(from Virnstein et al. 1983).

Area Seagrass

Sieve AbundanceFauna1 Coll. mesh Grass Sand G:Sgroup gear (mm) (G) (S) ratio Source

Indian River, FL

Chesapeake Bay, VA

Tampa Bay, FL

Biscayne Bay, FL

% Carrie Bow, BELIZESeto Sea, JAPAN

Chesapeake Bay, VA

Long Is. Sound, NY

Thalassia/HaloduIIIIII11

HaloduleZosteraZosteraHaloduleThalassiaHaloduleThalassiaThalassiaZostera

IIZosteraZosteraZostera

le MPCrDeFMMMPP

zMo+PMCrDeFF

cocococoDrcocococococococoSlSlTrTrSe

0.5 17,479 5,844 3.0 PS0.5 6,248 3,403 1.8 PS0.5 3,152 485 6.5 PS0.5 215 15 14.3 PS3.2 6.1 0.7 8.8 G (unpubl.)1.0 7,460 2,530 2.9 (1978)0.5 39,000 7,850 5.0 ; (1978)i.5"

0:5

48,900 13,313 8,462 1,160 42.2 1.6 0 ss (1974) (1977)

33,485

(7i4)

4.0 ss (1974)1.0

"iz1.6 OW (1967)

1.0 1.0 OW (1967)1.0 6,476 8,000 0.8-_ (2,755)

YY ii;;;;

__ (2,054) (824) :*; KK (1974)__ (17,292) '(:z:; 18:7 HO (1980)__ (1,090) (164) 6.7 OH (1980)__ (337,677) (139,264) 2.4 BO (1971)

M = macrobenthos, P = polychaetes, Cr = crustaceans, De = decapods, F = fishes, MO = mollusks. Collection gear: Co= corer, Dr = dropnet, Sl = sledge, Tr = trawl, Se = seine. References: PS = present study, G = Gilmore(unpubl.), V = Virnstein (1978), 0 = Orth (1977), SS = Santos and Simon (1974), OW = O'Gower and Wacassey (1967),YY = Young and Young (1982), K = Kikuchi (1974), HO = Heck and Orth (1980), OH = Orth and Heck (1980), BO = Briggsand O'Connor (1971).

organisms from seagrasses to organismsfrom sand is greatly in favor of theseagrass organisms, with ratios of up to42:l. However, a cautionary note must beadded: The ratios are highest in thetemperate zone stations and in turbidsubtropical areas such as Indian River.The three lowest ratios are from BiscayneBay, Florida, and Belize, which representnot only the most tropical stations, butalso those with the clearest water. It isquite possible, as in other facets ofseagrass ecology, that there are distinctdifferences in functional relationshipbetween temperate and tropical systems.However, studies from the west coast ofFlorida, which is a transitional area,suggest that here the grassbeds are denserand richer in invertebrate abundance thanthe adjacent habitats (Santos and Simgn1974; Hooks et al. 1976; Stoner 1980 ;Stoner et al. 1983).

Stoner (1980b) found that the density ofmacrofaunal organisms and the number ofspecies taken was directly related to thedensity of macrophyte biomass. Here thefauna1 dominance was different between thevegetated and unvegetated stations. Theanalysis of sediments showed that theparticulate size distribution did notdiffer and that differences in animaldensities could more directly beattributable to macrophyte biomass and notsediment characteristics.

In another study, in the Indian River,Virnstein et al. (1983) surveyed themacrofaunal invertebrates of seagrass bedsand nearby bare sand sediments and foundthat the seagrass beds supported threetimes the density of invertebrates and 38%more species compared with the adjacentsandy sediments. The abundance ofepitaunal organisms was 13 times greaterin the seagrass beds compared with thesand flats. In the seagrass beds 54% ofthe individuals were epifaunal compared to12% in the sand flats. Virnstein et al.(1983) also found that the epifaunalorganisms were much more trophicallyimportant, and consequently more heavilypreyed upon, than the infauna.

Table 15 summarizes numerous studies onthe relationship between the structuralcomplexity of seagrass beds and thedistribution and abundance of the

associated animal complex. Experimentalevidence suggests that grass bedinvertebrates actively select vegetatedhabitat rather than bare sand, indicatingthat habitat preference is an importantforce contributing to observed fauna1densities in grass beds. Selection oftenappears to be based on the form orstructural characteristics of theseagrass.

While the relative abundance ofinvertebrates in seagrass is usually highwhen compared to surrounding habitats, theactual numbers are highly variable. Largechanges in abundance and even the speciesencountered are frequently seen over smallchanges in space (Brook 1978) and time(Greening and Livingston 1982). Whencomparing strictly infaunal organisms, adifferent pattern may appear. Stoner(1983) found that the relative abundancesof infaunal organisms in sand decreased inthe order, Halodule, Syringodium,Thalassia, as well as from low to higherbiomass of the seagrasses.

The least-defined patterns ofdistribution and abundance are availablefor seagrass-associated meiofaunalorganisms. Bell et al. (1984) reviewedseagrass meiofaunal studies and concludedthat while little comparative literatureexists that can be directly intercompared,due to both a paucity of studies and thelarge differences in sampling techniquesand sample processing, their studiesconcluded that nematodes and copepods werethe most abundant taxa found in thesediments; that nematode densities werehigher in the sediments than on seagrassblades; and that copepod densities onblades were equal or greater than nematodedensities in the sediments in winter andspring.

5.1.2 Structure and Predation

With the correlation between the plantsand animal abundance established,questions followed addressing the natureof plant-animal interactions and how theserelationships shape community structure.Of particular interest is the role ofplants in mediating predator-preyinteractions. There is abundant indirectevidence that the grass carpet offersprotection from predation for the animals

60

Table 15. Summary of studies describing the influence of seagrass plant architecture on the associated animal distribution and abundance (fromOrth et al. 1984).

Feature- Taxa Function of seagrass

Animal speciesor community patterns Reference

Zostera marina rootsand rhiromes

Z. noltii rootsandrhizomes

Halodule wrightiileaves

Z. marina leaves

Thalassia testudinumleaves

2

I. testudinum, H.wrightii, Syringo-dium filiforme leaves~~

T. testudinum, S. fili-_forme-leaves -

T. testudinum, S. fili-_forme leaves -

Artificial leaves andrhizomes

macroinvertebrates, infauna

only, >0.5 mm

macroinvertebrates, epifaunaand infauna. >0.25 mm

macroinvertebrates, both in-fauna and epifauna, >l.Omm

amphipods as prey; pinfish,Lagodon rhomboides, andshrimp, Palaemonetes vul-garis, as predators

ampipods as prey; pinfish,Lagodon rhomboides, aspredator

amphipods as prey; pinfish,Lagodon rhomboides, aspredator

macroinvertebrates, infaunaand epifauna, >0.5 mm

amphipods

shrimp, Palaemonetes vulgar-is and Palaemon floridan-~,asprey,pinfish,Q-don rhomboides, as-predator

roots and rhizomes protect more species and individuals in vege- Orth 1977a,binfauna from predators tated than in bare sand areas

roots and rhizomes providespatial refuge from preda-tors

diverse and dense assemblage of fauna Reise 1978associated with vegetation. Greaterabundance of epifauna and infaunain dense eelgrass compared to lowdensity eelgrass

leaves serve as protectionagainst predation

predation rate decreases withincreasing blade densitybut not in linear function

degree of species specific se-lectivity function of macro-phyte biomass

blade surface area best esti-mate of habitat complexity

biomass of benthic vegetationindependent of sedimentgranulometry, exerts stronginfluence on abundance,dominance, diversity andtrophic organization of mac-robenthic infauna and epi-fauna

blade density and plantspecies composition me-diate predation

protection from predation

response pattern (increase or decrease) Young and Young1977depends on individual macrobenthic

species

susceptibility to predators depends onamphipod life style, i.e., infaunaor epifauna, tube builders, orepifaunal free-living forms

amphipod consumption diverged fromthat predicted by heavy macrophytecover; epifaunal forms preferred byfish predator more than infaunalforms

selection for high seagrass density,i.e., large surface area, based onvulnerability of amphipod topredation by Lagodon rhomboides

abundance of epifaunal amphipods andpolychaetes directly related tomacrophyte biomass. Infaunalamphipods inversely related tobiomass

majority of amphipod species associ-ated with seagrasses

shrimp less vulnerable to predation invegetated vs nonvegetated habitats.Competitive displacement of p. c-garis by p. floridanus made p. fi-e more susceptible to predation

Nelson 1979a,1979b, 1980

Stoner 1979

Stoner 1980a

Stoner 1980b

Stoner 198Oc

Coen et al. 1981

(Continued)

Table 15. (Continued).

Feature Taxa Function of seagrassAnimal species

or community patterns Reference

Artificial leaves andrhizomes

Z. marina roots and_l-hizomeS

Artificial leaves and b arenaria as prey, Calli-rhizomes ne=idus as predator

Z. marina shoots macroinvertebrates, both in-fauna and epifauna, >0.5 mm

Z. marina, artificial_leaves and rhizomes

g H. wrightii roots andrhizomes

2. marina whole plant

I. testudinum, S. Fili-forme.

vH. wright),-_

leaves

T. testudinum shoots_

T. testudinum whole_plant

y. wrightii leaves

shrimp, Palaemonetes pugio,as prey, killifish, Fundulusheteroclitus as predator

macroinvertebrate burrowersincluding polychaetes, echi-noderms, bivalves, andcrustaceans

shoot density affects foragingsuccess of predator

root-mats prevent hard bod-ied taxa from burrowingmore than soft bodied taxa

plant structure prevents dig-ging activities of predator

shoot density regulates struc-ture of developing community

two prey species, juvenile Cal-linectes sapidus and Muli-

leaves reduce predatory effi-

-lateralis as prey; adultciency of adult Callinectes

C. sapidus as predatorsapidus

two bivalve species, Chionecancellata and Mercenariamercenaria

two bivalve species, Prototha-ca staminea and Macoma-~ -nasuta

amphipods as prey, Lagodonrhomboides as predator

macroinvertebrates, both in-fauna and epifauna, >l.O mm

macrofauna, infauna and eip-fauna, >0.5 mm

juvenile red drum, Sciaenopsocellatus

roots and rhizomes functionas refuge from predationand bind sediments thusincreasing sediment com-paction

plant serves as protectionagainst siphon nipping byfish. Fish shift feeding tomore obvious M. nasuta- -

leaves reduce foraging effi-ciency of predator

standing crop does not affectspecies densities

increased habitat complexity

protection from predators,patchiness more importantthan plant length andabove ground biomass

significant survival of prey only athigh vegetation densities

size distributions skewed toward smallsizes in seagrass bed

increased bivalve survival in presenceof sparse and dense artificialvegetation

increasing diversity of fauna1 assem-blage with increasing shoot density

shallow-dwelling M. lateralis elimi-_(nated at all densltles of seagrassleaves. Juvenile C. sapidus pro-tected at three dTfferent densitiesof leaves

both clam species less vulnerable towhelk predation but shallower dwell-ing form more susceptible than deep-er dwelling form

bivalve densitities higher compared toclean sand; reduced siphon nippingin vegetation results in greater netgrowth of p. staminea

number of amphipods consumed de-creases with increasing seagrassbiomass, differences occur amongmacrophyte species. Predatorefficiency function of size

similar densities in bare sand andvegetation

greater numbers of species and greaterfauna1 densities in close proximityto seagrass shoots

more red drum along ecotone of sea-grass and bare sand than for morehomogeneously vegetated sites

Heck and Thoman1981

Brenchley 1982

Blundon and Kennedy1982

Homriak et al. 1982

Orth and van Mont-frans 1982

Peterson 1982

Peterson andQuammen 1982

Stoner 1982

Young and Young1982

Lewis and Stoner1983

Holt et al. 1983

(Continued)

Table 15. (Concluded).

8

Feature Taxa Function of seagrassAnimal species

or community patterns Reference

T. testudinum, H._wrightii, S. filiforme,

amphipods and tanaidaceans seagrass growth form andbiomass mediate distribu-

leaves, roots and tion and foraging behaviorrhizomes of important predators

1. marina and H.wrightii leaves, rootsand rhizomes

infauna and epifauna >1.2mm

seagrass growth mediates ef-fects of large epibenticconsumers

1. marina whole plant Mercenaria mercenaria seagrass baffles current, re-sults in higher particulatefood concentrations

relative abundance of crustaceansfunction of seagrass species andbiomass. Significance of sea-grass biomass in structuringcrustacean assemblages heldwithin, but not across, seagrassspecies

Stoner 1983

average density of epibentt,os 52xand of infauna 3x the levelobserved on the sand flat.Epibenthic predators reside ingrass bed by day and forage onsand flat at night

Summerson andPeterson 1984

growth rates of M. mercencariaparadoxically iiigher in seagrassbeds than bare sand, but may beconsequence of more particulatefood

Peterson et al.1984

living in it, with the dense seagrassblades and rhizomes providing cover forinvertebrates and small fishes, while alsointerfering with the feeding efficiency oftheir potential predators. Heck andWetstone (1977) hypothesized that thesignificant plant biomass, invertebrateabundance relationships observed inPanamanian grass beds largely resultedfrom predation pressure which is mediatedby the structural complexity of the grasscarpet. Stoner (1980b) observed thatnumbers of macrobenthic animals increasednoticeably in the fall with emigration offishes from grass beds in Apalachee Bay.Stoner (1979) also demonstrated that theamphipods consumed most frequently bypinfish were epifaunal. Given thebehavioral characteristics of amphipodsand the feeding preference of pinfish, itfollows (Nelson found) that infaunalamphipods were 1.3 times more abundantthan epifaunal tube-dwelling amphipods and4 times more abundant than free-livingepifaunal amphipods with the seasonalinflux of pinfish, reiterating the rolepredators play in controlling bothabundances and species composition withinthe grass carpet (Nelson 1979a; Stoner1979).

In laboratory experiments, Stoner (1980)found that common epifaunal amphipods werecapable of detecting small differences inthe density of seagrass and activelyselected areas of high blade density.When equal blade biomass of the threecommon seagrasses--Thalassia testudinum,Syringodium filiforme and Halodulewrightii--were offered in preferencetests, Halodule was chosen. When equalsurface areas were offered, no preferenceswere observed, suggesting that surfacearea was the grass habitat characteristicchosen. In later field studies, Stoner(1983) found that amphipods andtanaidaceans were most abundant in beds ofThalassia or Syringodium, intermediate inHalodule, and least abundant in bare sand,with a superficial correlation related toplant standing crop. However, Thalassiaand Halodule supported nearly equalnumbers when compared on a unit-biomass orunit-surface area basis. Syringodium wasconsistently higher than the other twospecies on a unit-surface area basis.

The shifts in amphipod abundanceappeared to be related also to therelative abundance of predators. InHalodule beds where amphipod abundance waslow, the number of predatory fish was 2 to2.5 times the abundance in beds of theother seagrasses. In particular, Stoner(1983) found that pinfish made up 67% ofthe fish population, and was the majoramphipod consumer.

Numerous attempts have been made toassess the role of predation on epifaunain structuring invertebrate populationsutilizing exclosure-caging experi-mentalmanipulations. Excluding fish predatorshas generally resulted in increases inspecies richness and density (Young et al.1976; Orth 1977b; Young and Young 1977),although the results can often beconfounding (Virnstein et al. 1983).Where increases did not occur, it wasassumed that decapod predators hadincreased sufficiently in numbers withinthe cages, presumably due to a releasefrom predation by fishes, that they inturn were capable of significantlyreducing fauna1 numbers within the grasscarpet (Young and Young 1977).

Virnstein et al. (1983) attempted todetermine the importance of small decapodcrustaceans as predators, while alsoadmitting that they were simultaneouslydemonstrating the problems anddifficulties of caging experiments. Inboth the seagrass and sand communities,nested cages were erected with an outercage 2 m square with 12 mm mesh, and aninner cage 1.4 m square with 3 mm mesh.Both extended above the surface of thewater. It was anticipated that, with theprotection afforded by the fine mesh, thesmaller organisms in the inner cage wouldincrease in abundance. In fact, theopposite occurred with the numbers ofsmall crustaceans and polychaetesdecreasing in the inner cages; largecrustaceans and fishes decreased innumbers somewhat, but also increased insize. The conclusion was that the largercrustaceans such as Penaeus duorarum,Palaeomonetes intermedius,heteroclitus,

and Alpheusand fishes such as

Bairdiella chrysura and Gobiosoma robustumentered the cages as juveniles and grazedheavily on the captive prey as they grew(Virnstein et al. 1983). In turn these

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intermediate sized organizms were releasedfrom predation pressure from largercarnivores. Leber (1985) alleviated suchproblems associated with cagingexperiments by documenting predatorspecies, using a smaller mesh size toexclude them, and employing short-termexperiments. He concluded thatdifferential predation could account forthe strong correlation of amphipods withmacrophyte abundance, whereas microhabitatselection was the primary factordetermining the strong relationshipbetween the abundance of the carideanshrimp Latreutes and plant biomass. Theauthor noted that the refuge value of theseagrass canopy depends on therelationship of prey size to canopyarchitecture, with smaller organismsafforded more protection from predation.The relative importance of predationavoidance versus microhabitat selection indetermining community structure amongseagrass prey organisms should vary due tophysical and behavioral differences amongthese populations (Leber 1985).

The above paragraph serves to illustratethe complex interactions between predatorand prey populations. Surprisingly littleis still known about the interaction offishes with the structural complexity ofthe grass canopy. Because of therestricted size of fishes typicallyinhabiting seagrass beds, Ogden and Zieman(1977) suggested that large predators suchas barracudas, jacks, and mackerels may beresponsible for restricting permanentresidents to those small enough to hidewithin the grass carpet. For fisheslarger than about 20 cm SL the grass bedcan be thought of as a two dimensionalenvironment; these fishes are too large tofind shelter within the grass carpet.Mid-sized fishes (20-40 cm SL) are thoughtto be excluded from the majority of thegrass beds by the larger predatorsoccasionally present; their activities arelimited to brief forays from the shelterof reefs or mangrove roots. Althoughthese fishes are restricted to areas ofshelter by day, they may move into thebeds at night when predation is lessintense (Ogden and Zieman 1977; Ogden1980).

Heck and Orth (1980a) have hypothesizedthat both abundance and diversity of

fishes should increase with increasingstructural complexity until the feedingefficiency of the fishes is reduced due tointerference with the grass blades orconditions within the grass canopy becomeunfavorable, at which point fish densitigsshould decline. Nelson (1979 >demonstrated that the predatory efficiencyof the uinfish on amohipods decreased withincreasing Zostera marina blade densities.Coen (1979) that with increasinacover of -red algae (Digenia simplex:Laurencia Gracilariaothersb)dththe'TifJ;-$ for$r;;a~micie~~~on andPalaemonetes vulgaris was reduced. Usingartificial seaarass. Heck and Thoman(1981) observed ieduced feeding efficiencyin the killifish, Fundulus heteroditus, onthe grass shrimp, Palaemonetes pugio, withincreasing grass density.

Attempts are being made to sift andsynthesize the information contained inthe large, and often bewildering, database now accumulating on the relationbetween the plant and fauna1 components ofthe seagrass community. In a review ofthe relationships of the plant structureon the predator-prey relationships inseagrass communities, Orth et al. (1984)developed the following "framework" forthe assessment of fauna1 abundance.

1. In general, epifauna are more sus-ceptible to predation by epibenthicpredators than infauna. Among theepifauna, tube dwellers and highlymobile species will be less suscep-tible than free-living and lessmobile species. For infaunalspecies, tube dwellers and burrowersliving at or below the rhizome layerwill be better protected than thoseliving above it. The depth at whicha prey species attains a refuge inthe sediments will be shallower in avegetated habitat than ’unvegetated habitat, provid:: t$species can burrow into or beneaththe rhizome layer.

2. The density of shoots, the patch-iness of the grassbed, plant bio-mass, individual leaf area, leafmorphology and the thickness, struc-ture and proximity of the rhizomelayer to the sediment surface are

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the key characteristics of the plantthat potentially can mitigate theeffects of predation. However, alinear relationship between some ofthese characteristics and predatorsuccess does not appear to exist.Instead, a threshold level of theseplant characteristics seems neces-sary for significant protection frompredation to occur. Because of thevariety of leaf sizes and shapespresent in the diverse seagrassspecies and the different character-istics of the prey and predatorspecies, this threshold level isvariable.

3. Heterogeneous grass beds (bare sandareas interspersed within the bed)should provide more favorable for-aging areas for motile fishes orinvertebrates, since motile fish orinvertebrates can forage over theunvegetated areas while at the sametime remaining in close proximity totheir protective vegetated habitat.Particularly important to juveniles,seagrass beds may serve as a refugefrom which animals may forage in amanner similar to a coral reef(Summerson and Peterson 1984). Inaddition, it is felt that, in themanner of optimal foraging strategy,prey organisms will "balance preda-tion risk with resource availabilityin order to maximize energy gain andgrowth" (Orth et al. 1984).

4. The predator-prey relationshipsdiscussed above can be affected byother equally important, yet poorlyinvestigated, biological and physi-cal processes that occur in thesemultispecies assemblages, such asadult-larval interactions (Woodin1976), adult-adult competitiveinteractions (Peterson 1979; Coen etal. 1981), macrofauna-meiofaunalrelationships (S.J. Bell, pers.comm. in Orth et al. 1984), andmigration patterns due to reproduc-tion and/or feeding, or response tostrong physical gradients such asday-night temperature differences(Adams 1976a; Robertson and Howard1978; Stoner 1980a). The behav-ioral, physiological, and morpho-logical differences among all the

species that utilize the seagrasshabitat, coupled with the influenceof the plant itself and its varia-tions in shoot density, biomass, andleaf area, all function to determinethe structure of fauna1 communities.

5.1.3 Fauna1 Sampling: The Problemsof Gear and Technique

A major difficulty with studying thisabundant fauna is the proper quantitativesampling of the organisms of interest. Noone set of gear or techniques samples allsegments of the community evenly, and somemethods are highly selective, which mustbe taken into account when comparingdifferent studies that use even slightlydifferent sampling gear or samplingschemes. For instance, the pink shrimp,Penaeus duorarum, is normally buried inthe sediments by day and active at night.Sampling schemes that utilized daytimetrawling would greatly underestimate theabundance of this and other organisms withsimilar habits.

When devices are used which yieldrelatively small quantitative samples,amphipods, isopods, gastropods, andpolychaetes are typically found to be mostabundant, (Nagle 1968; Carter et al. 1973;Marsh 1973; Kikuchi 1974; Brook 1975,1977, 1978; Lewis and Stoner 1981). Brook(1975, 1977) used a water-powered suctiondredge in a Card Sound Thalassia bed andfound that amphipods represented 62.2% ofall crustaceans captured. In ApalacheeBay, Lewis and Stoner (1981) compared thesampling results obtained by different-sized corers (5.5 to 10.5 cm diameter) andsieve sizes (0.5 and 1.0 mm) in a northernFlorida seagrass meadow. They found thatmost organisms collected were within theupper 5 cm of sediment, although all sizesof corers captured similar numbers ofspecies and showed very similar speciesaccumulation curves. However, the smallcorers yielded significantly greaternumbers of organisms, and many of thespecies that were undersampled with thelarger corers were those that were closelyassociated with the seagrass cover. Thisstudy also investigated the relativecapture efficiency of 2 sieve sizes, andfound that the 1.0 mm mesh retained only5l%-57% of the individuals captured on the0.5 mm mesh. The differences were due to

66

undersampling species with a smallterminal size as well as juveniles of thelarger species.

While the previously described studiesaddressed the efficiency 0:different-sized core samplers, therelative efficiency of corers comparedwith suction samplers was examined byStoner et al. (1983) for vegetated andunvegetated sites in Pensacola Bay. Theyfound that with similar mesh sizes forsieving of the cores and for the filterbag of the suction sampler (0.5 mm) bothsamplers collected similar numbers ofspecies. The corers, however, yielded 33%more individuals from a Haloduie bed, and73% more individuals from a bare sandhabitat than the suction sampler whencompared on an equal-area basis.

The other major type of sampling deviceused in sampling fauna in and aroundseagrass beds is some form of trawl,whether a fixed-frame or beam trawl, or adevice such as an otter trawl, whichrequires a certain velocity through thewater column to maintain the trawl in theexpanded condition in which it is able tofish. In collections in seagrass bedswhere these sampling devices have beenused, decapods (including penaeid andcaridean shrimp and true crabs) andgastropods generally dominate numericallyin invertebrate collections (Tabb andManning 1961; Tabb et al. 1962; Roesslerand Tabb 1974; Yokel 1975a, 1975b; Hookset al. 1976; Thorhaug and Roessler 1977).

Trawl sampling for organisms, especiallyfishes, in the clear waters of manyseagrass beds can yield highly variableresults that greatly underestimate themobile fish fauna within a grassbed. Whenvisibility underwater is 10 to 20 meters,it requires no great effort for highlymobile organisms to evade the trawls thatare deployed behind small boats. Dropnets have been used effectively in shallowwater environments, but can be difficultto construct and are not useful in deeperwaters. For clear waters and deeperseagrass beds, a diver-deployed encirclingnet has proved highly effective andreplicable (Robblee and Zieman 1984).

Somewhat paradoxically, small andintermediate-sized organisms, such as

amphipods and caridean shrimp often arecaptured in large numbers by trawls, whosemesh size is nearly always larger thanamphipods. The trawls are usually notdirectly capturing the animals, however,but instead are efficiently capturing thesessile drift algae which the organismsare utilizing for shelter.

While it is important to recognize thatsome data will reflect sampling-gearselectivity, it should not obscure thefact that definite patterns of speciesabundance exist in seagrass meadows whencompared to adjacent habitats.

5.2 GENERALTROPHICSTRUCTURE

Seagrasses and associated epiphytesprovide food for trophically higherorganisms by means of three distinctroutes: (1) direct herbivory, (2) detritalfood webs within grass beds, and (3)exported material that is consumed inother systems, either as macroplantmaterial identifiable with the naked eye,or as detritus. Despite the fact thatseagrasses have a relatively high proteincontent (see Section 2.3), they aredirectly grazed by relatively few animals.

The most vexing questions surroundingseagrass food webs continue to relate tothe relative roles of detrital andmicroalgae-epiphyte grazing pathways, andthe functional processes andintermediaries by which the detrital foodpathway supplies nutrition to consumers.Most studies continue to show that theprimary pathway of energy and nutrienttransfer is through the detrital food web,and in many systems it may be the onlysignificant food web. During the past fewyears, new information has been gatheredon the relative role of the other modes ofutilization, in particular, the role ofactive epiphyte grazers, a pathway thathas previously been recognized but littlestudied. The picture emerging is that allof the pathways exist, but find differentdegrees of expression, depending on localconditions and the consumers present.While the detrital food web appears to bethe primary pathway of trophic energytransfer, any of the others may bequantitatively the most important atspecific sites.

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5.2.1 Seagrass Grazers

Throughout south Florida and in thegrassbeds of the Caribbean, often largenumbers of direct consumers ingest livingseagrass leaves in significant quantities.These include several species of seaurchins, the queen conch, numerous fishes,the green turtle, the Caribbean manatee,and assorted invertebrates, especiallycrustaceans and gastropods (McRoy andHelfferich 1980; Ogden 1980; and Zieman1982). In south Florida, grazing onseagrasses is highest in those grassbedsof the Florida Keys and outer margin ofFlorida Bay which are in relatively closeproximity to coral reefs. Major seagrassconsumers in that area are parrotfish(Scaridae) (Randall 1965; Ogden and Zieman1977): surgeonfishes (Randall 1967;Clav1 JO 1974), porgies and halfbeaks(Randall 1967). With increasing distancefrom the reef tract or patch reef, theintensity of grazing by large parrotfishand acanthurids decreases. The dominantgrazers become the small grassbed-dwellingparrotfish, typified by the bucktoothparrotfish Sparisoma radians and seaurchins, the most abundant of which isusually Lytechinus variegatus, althoughEucidaris * tribuloides Tripneustesventicosus and juvenile Djadema antillarumare also foundal.

g, seagrass beds (Moore et1963a, 1963 ; McPherson 1964, 1968;

Randall et al. 1964; Kier and Grant 1965;Moore and McPherson 1965; Ogden et al.1973; Prim 1973; Greenway 1976; andothers).

Assessments of the quantitative impor-tance of direct seagrass consumption haveappeared only recently, and for relativelyfew areas. The tacit assumption is thatfew organisms consume seagrasses directly,and that herbivory has substantiallydecreased with the decline of the popula-tions of green sea turtles and manatees.Like many assumptions of tropical andsemi-tropical ecosystems, this resultedfrom too much reliance on analogy fromtemperate-zone seagrass systems, and apaucity of direct observation. When thewidespread use of scuba enabled prolongedunderwater observation, the grazingeffects of some groups of direct consumerswere instantly recognizable, namely thepaper-punch, half-moon shaped holes pro-duced by parrotfish grazing on turtle

grass. By comparison, the ragged edgeproduced by urchin grazing is not obvious,and usually resembles a leaf that has beenphysically torn, until one learns to lookcarefully for the stepwise nibble marks.The grazing effects of green turtles andmanatees are not obvious until one learnswhat to look for, and are increasinglydifficult because of the rarity of theanimals and the decreased likelihood ofobserving them feeding.

The green sea turtle, Chelonia mydas, isa diurnal grazer of seagrass meadows. Thegrazing behavior of the green turtles issimilar to some of the large, reefparrotfish in the sense that they grazethe seagrass meadows and seek shelter atnight, frequently in deep holes or nearfringing reefs, surfacing at intervals tobreathe. The turtles then swim someunknown distance to the seagrass beds tofeed. What is unique is that they returnconsistently to the same spot and regrazethe previously grazed patches, maintainingblade lengths of only a few centimeters(Bjorndal 1980). The persistence of thesecharacteristic patches of neatly croppedleaves provides indirect evidence ofturtle grazing. Thayer et al. (1982) havecalculated that an intermediate sizedChelonia (64 kg) consumes daily about280 g dry weight of Thalassia blades.Turtle consumption of seagrass has beenestimated to be 2.2% of body weight perday (Thayer et al. 1980), 1.65% (Bjorndal1980), and 0.6% (Fenchel et al. 1979).

Turtles do not consume the entire bladeon their first graze of an area, but biteonly the lower portion and allow theepiphytized upper portion to float away(Bjorndal 1980; Zieman et al. 1984a).Many researchers assumed that the epiphytecomplex at the tip of seagrass leaves wasof higher food value than the plainseagrass leaf, but other studies haveshown that the basal portion of the greenleaves is higher in nitrogen concentrationthan the epiphytized tips (Mortimsr 1976;Bjorndal 1980; Zieman et al. 1984 ). Thenitrogen content of Thalassia leavesdecrease with age as well as withepiphytization. The basal portion ofThalassia leaves from St. Croix contained1.6% to 2.0% N on a dry weight basis,while the older brown tips of these leavescontained 0.6% to 1.1% N, and the

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epiphytized tips ranged from 0.5% to1.7% N (Zieman et al. 1984a). Thus, thecurrent evidence indicates that the greenseagrass leaves contain more nitrogen thaneither the senescent leaves or theleaf-epiphyte complex. By successivelyrecropping leaves from a plot, the turtlemaintains a diet that is consistentlyhigher in nitrogen and lower in fibercontent than whole leaves (Bjorndal,1980). The maximum length of grazing timeon one distinct patch is not known, butOgden (West Indies Lab, St. Croix, USVI,pers. comm.) has observed patches thathave been repeatedly grazed for up to ninemonths.

Manatees can weigh over 1000 kg and havebeen reported to consume up to 20% oftheir body weight per day in aquaticplants. When feeding on aquatic plants,manatees have been reported to feedindiscriminately on available plants(Hartman 1969). While in marine seagrassmeadows, manatees dig into the sedimentusing their stiff facial bristles, thenuproot the plants and shake them free ofadhered sediment. A similar mode offeeding has been observed in manateesfeeding in Thalassia beds by this author.Feeding patches average from 30 by 50 cmup to about 50 by 50 cm and usually form aconspicuous trail in seagrass beds. Theexcess sediments from the hole created byplant removal are mounded on the side ofthe holes as if the manatee had pushedmuch of it to the side before attemptingto uproot the plants.

In the Caribbean and south Florida, theamount of material grazed directly isrelatively high. It has been estimated(Odgen 1980) that direct grazing onseagrasses is higher in the Caribbean thanin any other marine area. In St. Croix ithas been estimated that an amountequivalent to 5%-10% of daily productionof Thalassia is directly consumed,primarily by Sparisoma radians andsecondarily by the urchins Diademaantillarum and Tripneustes ventricosus andonlv about 1% was exported. while 60% to100% of the productio'n of Syringodium wasexoorted (Zieman et al. 1979). Thus about70% of the daily production'of seagrasseswas available to the detrital system. InKingston Harbor, Jamaica, 0.3% of theproduction of Thalassia was consumed by

Sparisoma radians, 48.1% was consumed bythe urchin, Lytechinus variegatus, 42.1%was deposited on the bottom and availableto detritivores, with the remaining 9.5%being exported from the system (Greenway1976).

The values from St. Croix are similar toother studies in the Caribbean and southFlorida (Zieman, unpubl. data), althoughthe Jamaica study may overemphasize thequantity of seagrass material entering thegrazing food chain since urchins are notnormally found at densities of 20 urchinsper square meter as were found in KingstonHarbor (Ogden 1980). While the overallquantitative importance of urchin grazingon the seagrasses of the west coast ofFlorida has not been determined, severalreports indicate that, at times it can belocally significant. A population"explosion" of Lytechinus variegatus offthe coast of Dixie County, Florida,resulted in densities of 636 m-2 inaggregates of urchins, which denudedapproximately 20% of a seagrass bed (Campet al. 1973). In Apalachee Bay, Zimmermanand Livingston (1976a) reported that thisurchin was observed to graze Thalassialeaves down to substrate level, andpostulated that this was, at least inpart, responsible for low macrophytebiomass at certain stations. Urchins werealso present at stations with low seagrassbiomass near Florida State MarineLaboratory (R.L. Iverson, pers. comm.).Grazing by the few remaining sea turtlesand manatees is very localized andreduced. While the shallow seagrassmeadows of south Florida are used by fewducks, geese, and related waterfowl, theshallow bays and estuaries of the upperwestern coast of Florida offer abundantwaterfowl for viewing of hunting, as thisarea is used extensively as either aresting stop or for wintering. Directgrazing by these birds of the Ruppiacommonly found in low-salinity and inshoreareas of upper western Florida is afeature of this area not seen furthersouth.

An important by-product of heavy grazingon living seagrasses is an increase in theturnover rate of the standing crop ofleaves and the increased production ofdetrital particles from the fragmentationof living seagrass blades following

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feeding and passage through the gut(Thayer et al. 1984a; Zieman et al.1984a). In addition, the manner offeeding by green turtles, urchins, andparrotfish results in the release of oftenlarge quantities of torn or fragmentedliving seagrass and its subsequentdeposition as litter locally or afterexport from the bed (Greenway 1976; Ziemanet al. 1979).

5.2.2 Epiphyte-Seagrass Complex

Many of the literally hundreds ofspecies of small organisms in grass bedsutilize algal epiphytes and detritus astheir food sources. Gastropods,polychaetes, as well as amphipods,isopods, crabs, and other crustaceansingest a mixture of epiphytic and benthicalgae as well as detritus (Odum and Heald1972). As research continues, it isbecoming apparent that this represents oneof the major energy transfer pathways tohigher organisms. As one progresses fromthe clear, low-nutrient waters of theCaribbean and the Florida keys, to themore turbid and higher nutrient waters onthe west coast of Florida, there is anapparent increased dependence on theepiphytic grazing pathway (Fry 1984;Kitting et al. 1984).

In addition to those organisms whichfeed mainly on the epiphytes of oldseagrass leaves, many species that ingestprimarily seagrass, such as theparrotfish; will preferentially graze theepiphytized portion of the seagrass blade.As a result, seagrass epiphytes may bequite important in the flow of energywithin the grass carpet. Many of thesmall, mobile epifaunal species soabundant in the grass bed and important asfood for fishes, feed at least in part onepiphytes. Tozeuma carolinense, a commoncaridean shrimp, feeds on epiphytic algaeattached to seagrass blades; undoubtedlyepifauna are consumed coincidentally(Ewald 1969). Three of the four commonsouth Florida seagrass-dwelling amphipodsutilize seagrass epiphytes, seagrassdetritus and drift algae as food sources,in this order of importance (Zimmerman etal. 1979). Eoinhvtic alaae were eaten ata high rate by' Cymadusa"compta, Gammarusmucronatus, and Melltanitida. The algaewere also assimilated more efficiently by

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these amphipods (48%, 43%, and 75%respectively) than other food sourcestested, including macrophytic drift algae,live seagrass and seagrass detritus.

Kitting (1984) has used a uniquemonitoring system to show that grazing ofsmall invertebrates is highest while theinvertebrates are on the upper grassblades at night and not while at the baseof the leaves among the detritus. It issuggested that these grazers select therapidly growing ephemeral algae whenavailable, but that detritus may beimportant when the algae are not availableor overgrazed. Kitting et al. (1984)later showed that in Texas estuaries, de113C ratios suggested a higher assimilationof epiphyte carbon than seagrass carbon.Fry (1984) obtained similar results in astudy in the Indian River in Florida, butnoted that the dominant seagrass there wasSyringodium which floats- readily anddrifts from the bed with littlecontribution to the local detritus. Inthe Texas estuaries and the Indian River,the turbidity is very high, and epiphyticgrowth is very high compared with that inthe south Florida estuaries. Epiphytesare thus a higher potential food sourcethan in clearer waters where the epiphyticgrowths are relatively lower. In highlyeutrophic and turbid estuaries, epiphyticgrazers can be essential to the health ofthe seagrasses. Orth and van Montfrans(1984) have shown that in estuaries withexcessive nutrient loads, the eliminationof epiphytic grazers can cause the deathof seagrasses when epiphytes proliferateand block incoming light on the surface ofleaves, restricting seagrassphotosynthesis.

5.2.3 Oetrital Feeding

Detritus food webs are consistentlyconsidered to be the major pathway throughwhich energy flows in seagrass ecosystems.In areas where it is present, Thalassiagenerally forms the predominant fractionof the decaying material, with Syringodiumand Halodule nearly always forming a minorportion of the detritus. Seagrass litterdecomposes by being broken down over aperiod of months by bacteria, fungi andother organisms. In Biscayne Bay, Fenchel(1970) found that Thalassia was theprincipal detrital component present

(87.1%); other portions included: 2.1%other seagrasses, 4.6% algae, 0.4% animalremains, 3.3% mangrove leaves, and 2.5%terrestrial material. The microbialcommunity living in the detritus consistedmainly of bacteria, small zooflagellates,diatoms, unicellular algae and ciliates.These types of organisms form the majorsource of nutrition for detrital feeders.

Detrital consumers ingest entireparticles, but also strip bacteria andother organisms from the detritus. Veryfrequently detrital feeders arecoprophagous, with the recently releasedfecal pellet being subsequently reingestedfollowing a time during whichrecolonization and regrowth of themicrobes occurs (Fenchel 1970).

Mullet and other fishes are abundant andimportant feeders on detrital particlesand benthic microalgae throughout theentire gulf region (Odum 1970). Carr andAdams (1973) found that detritusconsumption was of major importance in atleast one feeding stage of 15 out of 21species of juvenile marine fishes,including sparids, hemiramphids, blennies,gobies, atherinids, clupeids and atetraodontid.

As Stoner (1979) and Livingston (1982a)noted, it can be difficult to impossibleto define when an organism is a truedetritivore, because many detritivorousorganisms are highly omnivorous organisms,consuming many other available substrates,in addition to organic detritus. Mostpenaeid and caridean shrimp are consideredto be omnivores, but they are highlydependent on detritus as juveniles,becoming more omnivorous, evencarnivorous, as adults. Penaeus OdCorarumthe pink shrimp, in addition to organi:detritus, consumes sand, polychaetes,nematodes, caridean shrimp, mysids,copepods, isopods, amphipods, ostracods,mollusks and foraminiferans (Eldred 1958;Eldred et al. 1961). Several of the largeand conspicuous invertebrates such as thegastropod, Strombus gigas, and theasteroid, Oreaster reticulatus, whileprimarily consuming other substrates, willingest seagrass litter and detritus as apart of their food (Randall 1964;Scheibling 1980). In the seagrass meadowsof the upper Florida coast numerous

mollusks and polychaetes have beenrecorded as consuming detritus (Bloom etal. 1972; Santos and Simon 1974; Young andYoung 1977).

5.2.4 Carnivory

Typically the infauna in seagrass bedsis not as heavily preyed upon as theepifauna (Kikuchi 1974, 1980). Theprotection from predation afforded theinfauna of grass beds by dense leafcanopies and by the fibrous rhizome matsof the more robust species of seagrasslike Thalassia, is great enough that fewfishes specialize on infauna when feeding(Orth 1977). In the Indian River, Youngand Young (1977) found that epifaunalcrustaceans such as Cymadusa compta,Melita elongata, and Erichsonellafiliformis, which were apparently heavilypreyed upon by fish predators, increasedin abundance during exclusion experiments,while the infaunal species were notaffected. Stoner (1983) noted lowabundances and smaller sizes of epifaunalamphipods at Halodule sites, relative toThalassia and Syringodium sites. Bycomparison, bottom dwelling and infaunalamphipods showed nearly uniformdistribution in both aabundance and size ofthe organisms among all the seagrasses.

Stoner (1983) believed that the increasein abundance of certain infaunal tanaidsand amphipods in Halodule beds was due tothe "thick, tough underground mat of rootsand rhizomes produced by Halodule," andthat "this underground complex may providea more effective refuge from invertebratepredators than the larqe diameter rhizomesand sparse roots o‘i Syringodium andThalassia." While the assumptionsdescribed here may be valid, theexplanation does not seem consistent withother observations. Halodule bedscharacteristically have fine-grainedsediments which fishes like sea trout(Cynoscion) readily forage, whileThalassia beds are much more stabilizedand resistant to penetration, makingforaging by infaunal feeders much moredifficult (Zieman, 1982). Much work yetremains in determining the controls onabundance of infaunal organisms inseagrass beds and surrounding areas.

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Some organisms are quite flexible intheir response to prey abundance. Theblue crab, Callinectes sapidus, has beenobserved to shift its feeding from Zosterainfauna to epibiota. Because of theprotectiveness of the rhizome layer to theinfauna, and the accessibility of theepifauna, the impact of blue crabpredation may be greatest on epibenthicfauna (Orth 1977b).

Many of the important top carnivorespresent on the grass flats of southFlorida also inhabit the seagrass meadowsthroughout the western coast of Florida.These include the widely distributed lemonshark (Negaprion brevirostris) and thebonnethead shark (Sphyrna tiburo), thetarpon (Megalops atlanticus), thelizardfish (Synodon foetens), the coronetfish (Fistularia tobami the barracuda(Sphyraena barracuda), carangids, the greysnapper (Lutjanus griesus), and thespotted seatrout (Cynoscion nebulosus).While some of these carnivores areresident, such as the lizardfish and thegray snapper, others, like the tarpon,undergo extensive seasonal migrations.

5.2.5 Trophies and OntogeneticDevelopment of Grassbed Fishes

Carr and Adams (1973), Stoner (1979),and Livingston (1980b) have alldemonstrated ontogenetic changes in thefeeding habits of fishes inhabitingseagrass meadows on the west coast ofFlorida. Much of the work has emphasizedthe life history changes in the feedinghabits of the pinfish, which is one ofthe most abundant fish throughout the areaand is extremely important as a foragefish. Although the pinfish undergoesprogressive trophic changes withdevelopment, detritus and seagrasses are acomponent of its diet at all stages(Stoner 1979; Livingston 1980b). As anadult, usually 75% to 90% of its dietconsists of seagrasses or detritus andplant debris. Livingston (1982a)investigated the trophic organization of14 fish species over an eight year periodin the shallow grass beds of ApalacheeBay. He divided the fishes into threemajor trophic groups. The first group wasprimarily planktivorous forms and includedthe early life stages of anchovies, spot,mojarras, and pinfish. These juveniles

72

feed primarily on copepods, amphipods, andplant debris and detritus. The earlieststages of the pinfish and spot occur inlate winter when they selectively feed onplanktonic copepods. With development,all become more omnivorous; the spot andthe mojarras become primarily benthicfeeders. The second major grouping ofLivingston (1982a) is primarily composedof benthic omnivores and carnivores.Included in this group are theintermediate stages of the pinfish, thespotted pinfish Diplodus holbrooki, andthe monacanthids. While the monacanthidsshow similar feeding habits, the twopinfish species showed little dietaryoverlap despite being both temporally andspatially sympatric (Livingston 1982a).With further development, the pinfishbecomes primarily an herbivore. The thirdgroup contained the pigfish, Orthopristischrysoptera, the silver perch, Bairdiellachrysura, and the pipe fish Sygnathusfloridae, which may be generalist feedersj u v e n i l e s ,as but specialize oncrustaceans such as shrimp, crabs, andamphipods as adults. While some speciesshowed the progressive trophic changeswith development, others such as the bayanchovy, Anchoa mitchilli, and the bandedblenny, Panus fasciatus, showed morepersistent feeding patterns throughouttheir development.

5.3 DECOMPOSITIONANDDETRITAL PROCESSING

Detrital food-web theory in marine andaquatic ecosystems is based on the conceptthat for the majority of animals thatderive all or part of their nutrition frommacrophytes, the greatest proportion offresh plant material is not readily usableas a food source. For these organisms,macrophyte organic matter becomes a foodsource of nutritional value only afterundergoing decomposition to particulateorganic detritus, which is defined as deadorganic matter along with its associatedmicroorganisms (Heald 1969).

This section will describe only brieflythe detrital food-web concept and willthen discuss recent work that is pertinentto the understanding of detrital food websin seagrass ecosystems. Numerous generalreview papers exist on the subject ofdetrital processing and detrital food-web

theory relating to seagrass systems; amongthem are Fenchel and Jorgensen (1977), Lee(1980), Tenore and Rice (1980), andNedwell (1983). Review papers directedmore specifically to seagrasses includeFenchel (1977), Klug (1980), Robertson(1982), and Thayer et al. (1984b). Recentand significant work is reported in theProceedings of the Symposium on DetritusDynamics in Aquatic Ecosystems (Roman andTenore 1984). Much of this section hasbeen liberally (and literally) extractedfrom two previous works (Zieman 1982,1987).

As plant litter begins to decay, itgenerally passes through threerecognizable phases (Godshalk and Wetzel1978). The first phase is a rapid weightloss due to leaching and autolysis ofplant compounds. This phase is generallyvery rapid and the materials released arereadily utilized by a variety oforganisms. In the second phase, decay isslower and weight reduction is due to acombination of fragmentation and thesimultaneous degradation of the substrateby microbial activity. At the end of thisphase, the remaining substrate is highlyrefractory and of greatly lowered foodvalue. (Although the material may have arelatively high caloric value, thecalories are in the form of structuralcompounds which most organisms cannotdegrade enzymatically.) The third phaseof decay involves the relatively slowdecomposition and fragmentation of thishighly resistant residual material.

Depending on the source material andenvironmental conditions, this degradationprocess may take from several weeks toyears. Increasing resistance todegradation is roughly in the order:algae, seagrasses, salt marsh plants, andmangroves. The rate of degradation isincreased by physical breakdown andfragmentation, alternate wetting anddrying (Zieman 1975a), the action ofgrazers (Fenchel 1970; Morrison and White1980), and increased nutrients in themedium (Fenchel and Harrison 1976).

During decomposition and detritusformation, the size of the particulatematter is decreased, making it availableas food for a wider variety of animals.This size reduction may be the result of

simple physical agitation, or of grazingby active detritivores, such as amphipodsand isopods. Reduction of particle sizeincreases the surface area available formicrobial colonization, thus increasingthe decomposition rate. The fine detritalparticles, whether utilized locally assuspended or deposited organic matter ortransported by the water to distant areas,provide food for trophically importantfauna of seagrass beds and adjacentbenthic communities, such as polychaeteworms, amphipods, isopods, ophiuroids,certain gastropods, and mullet.

The food value of detritus has commonlybeen considered a function of the nitrogencontent of the material (Odum and de laCruz 1967). However, considering nitrogencontent alone can overestimate thenutritional value of the material since upto 30% of the nitrogen can exist intightly bound non-protein fractions(Harrison and Mann 1975b; Suberkropp etal. 1976; Odum et al. 1979). Asdecomposition progresses, the non-proteinnitrogen fraction can increaseproportionally to total nitrogen yieldinga food source of lower value as the resultof several processes: complexing ofproteins . the(Suberkropp 'e?t al.

lignin fraction1976); production of

chitin, a major cell wall compound offungi (Odum et al. 1979); anddecomposition of bacterial exudates (Leeet al. 1980). However, protein (Thayer etal. 1977) and amino acid (Zieman et al.1984c) have been shown to increase in somemacrophytes during decompositionpresumably leading to an enriched foodsource. Inhibitory compounds found inmacrophyte leaves have also been found todecrease in older and decomposingmacrophyte leaves and litter (Harrison andChan 1980), which may increase theirpalatability to consumers.

Bacteria, fungi, and othermicroorganisms have the enzymatic capacitythat many animals lack to degrade theincreasingly refractory macrophyte organicmatter! converting a portion of it tomicrobial protoplasm and mineralizing alarge fraction. Whereas nitrogen istypically 2% to 45% dry weight ofseagrasses, microflora contain 5% to 10%nitrogen. The microflora may use nitrogenfrom the macrophyte substrate, but they

73

also have the capacity to incorporateinorganic nitrogen from the surroundingmedium (either the sediments or the watercolumn) into their cells during thedecomposition process, thus enriching thedetritus with proteins and other solublenitrogen compounds. In addition, carboncompounds of the microflora are much lessresistant to digestion than the fibrouscomponents of macrophyte litter. Thus, asdecomposition occurs there will be agradual mineralization of the highlyresistant fraction of the seagrass organicmatter and corresponding synthesis ofmicrobial biomass that contains a muchhigher proportion of soluble compounds.

In addition to the refractory materialof detritus, the dissolved organic carbonand nitrogen, released by seagrasses (DOCand DON) during both growth anddecomposition, provide nutrition formicrobes. The DOC-DON fraction releasedduring growth and early decompositionstages is readily utilized, containingmuch of the soluble carbohydrate andprotein of the plants. It is quicklyassimilated by microorganisms, but isgenerally available to consumers as foodin significant quantities only after theconversion to microbial biomass. Duringphotosynthesis, living Thalassia leaveswere found to release 2% to 10% ofrecently-fixed material (Wetzel andPenhale 1979). Fresh-dried Thalassia andSyringodium leaves released 13% and 20%respectively of their organic carboncontent during leaching under sterileconditions (Robertson et al. 1982). Thisdissolved fraction was rapidly assimilatedby microbial organisms, and in 14 days theDOC released by Thalassia and Syringodiumleaves supported 10 times more microbialbiomass per unit of carbon than did theparticulate fraction (Robertson et al.1982).

A major tenet of detrital food-webtheory has been that microorganisms are anecessary trophic intermediary between themacrophyte litter and detritivorousanimals. Much evidence suggests thatthese consumers derive the largest portionof their nutritional requirements from themicrobial component of detritus (Fenchel1970; Hargrave 1970; Tenore 1977; see alsoa review in Levinton et al. 1984).Detritivores assimilate microfloral

compounds with high efficiencies, rangingfrom 50% to nearly lOO%, often with lowcorresponding assimilation of detritalplant compounds (Yingst 1976; Lopez et al.1977; Cammen 1980). Deposit feedingmollusks were found to remove nitrogenfrom sediment particles by removal of themicroorganisms but did not measurablyreduce the total organic carbon content ofthe sediments which was presumablydominated by detrital plant carbon (Newell1965). When the nitrogen-poor,carbon-rich feces were incubated inseawater, their nitrogen content increaseddue to the growth of attachedmicroorganisms. A new cycle of ingestionby the animals would again reduce thenitrogen content as the fresh crop ofmicroorganisms was digested. By selectivegrazing, amphipods and other crustaceansingested the microbial component on leaflitter without ingesting the substrate(Morrison and White 1980). However, thegrazing action of detritivores can alsohave a positive feedback and enhance theproduction of microbial populations on thedetrital particles. Microbial respirationrates associated with macrophyte detrituswere stimulated bv the feedina activitiesof animals, possibly as a- resultphysical fragmentation of the detri(Fenchel 1970; Foulds and Mann 1978) orthe removal of inhibitory decompositproducts (Lee 1980).

While the importance of the microbcomponents of detritus to detritivores

of

bu;on

alis

firmly established, other studies haveindicated that consumers may be capable ofassimilating the plant substrate (Fouldsand Mann 1978). In some instances, thehigh abundance of particulate materialcompensates for its low assimilationefficiency (Hargrave 1976). Cammen (1980)found that only 26% of the carbonrequirements of a population of depositfeeding polychaetes would be met byingested microbial biomass, although themicrobial biomass could supply 90% of thepopulation's nitrogen requirements. Thuswhile microbial biomass is assimilated athigh efficiencies of 50% to 100% (Yingst1976; Lopez et al. 1977) and can supplyproteins and essential growth factors, thelarge quantities of plant material thatare ingested also may be assimilated atlow efficiencies (less than 5%) to supplycarbon requirements.

74

In its broadest form, the detrital foodweb still seems the most applicable to thewidest array of seagrass systems. In manyareas, undoubtedly detrital and epiphyticfood sources are used jointly, based onthe relative availability and food valueof the material.

The wide variety of information nowavailable permits us to re-examine therole of seagrasses as food sources and themanner in which that food is utilized byconsumers. Fundamental to thisre-examination is the recognition that theinitial composition of macrophyte littervaries widely, and that this variationaffects the food value of the initialmaterial, the decomposition rate of thematerial, and the functioning of themicrobial community (Tenore 1977, 1983;Rice 1982). The variation in compositionis not only a function of species or typeof plant, i.e. Thalassia vs Spartina, butalso a function of the source of thematerial, with Thalassia showing a widevariation in nutritional content as afunction of the latitude in which it grew.This variation can affect strongly theapparent trophic role of the seagrasses inindividual seagrass beds.

Although seagrasses are marinemacrophytes, they are different in manyways from their counterparts, salt-marshplants and mangroves, with which they arefrequently compared. Seagrass leaves, forinstance, are initially much higher innitrogen content than either salt-marshplants or mangrove leaves, when eachenters the system under normal conditions(Rice 1982), and contain up to 4% totalnitrogen (Zieman et al. 1984c) and up to25% protein (Vicente et al. 1980; Dawesand Lawrence 1983). While the senescentleaf tips are low in nitrogen, the basesof recently detached leaves usually retaina significant proportion of living greenmaterial.

During decomposition, mangrove andsalt-marsh material increases in nitrogencontent (Odum and de la Cruz 1967; Heald1969; Rice 1982), while seagrasses remainrelatively constant (Rice 1982), ordecrease somewhat (Zieman et al. 1984c).Similarly, the protein and amino acidcontent of mangroves rise duringdecomposition but show less or no change

for seagrasses (Rice 1982; Zieman et al.1984b).

When decomposed under similarconditions, the stable isotope ratios ofcarbon did not change for eitherseagrasses or mangroves. The stableisotope ratio of nitrogen did not changeduring seagrass decomposition, but changedmarkedly for mangrove (Zieman et al.1984c). The mangrove litter also showedmuch greater uptake rates of ammonium pergram of plant litter (R.T. Zieman, unpubl.data). From this and other parameters itwas concluded that the seagrassdecomposition primarily used the internalnitrogen pool while the mangroves requiredextensive exogenous nitrogen input by themicrobes.

In another study, Roger Zimmerman (NMFS,Galveston, TX.; pers. comm.) found thatamphipods from seagrass and mangrovehabitats survived on seagrass detritus andsoon acquired the seagrass carbon isotopesignature. When fed on mangrove detritus,the amphipods from the seagrass habitatcould not obtain sufficient nutrients anddied. Those naturally occurring in themangrove habitat survived, but never fullyacquired the mangrove isotope signature.The conclusion of this study and that ofZieman et al. (1984) is that detritalconsumers can obtain more nutritionalvalue from the seagrass substrate thanfrom the mangrove substrate, and that manyorganisms cannot be sustained solely bythe microbial flora of refractorysubstrates such as mangrove detritus.Findlay and Tenore (1983) and Tenore etal. (1984) found similar patterns betweenthe macroalga Gracilaria containingrelatively available nutritive componentsand the marsh grass Spartina, a refractorysubstrate similar to mangroves.

In addition to compositional differencesbetween seagrasses and other macrophytesthat can lead to different mechanisms ofdecomposition, the plants themselves varywidely among locales. Dawes and Lawrence(1983) showed a shift in the proteincontent of Thalassia leaves from 13% inTampa Bay, to 16% at Key West, to 25% inBelize. Thus, within a single species themode of decomposition and the quality ofthe resulting detritus, which affects bothinitial and ultimate food value of the

75

material, may be quite different dependingon regional origin.

Synthesis. From the diverse studiesdescribed above, a pattern emerges of therelative utility of the detrital substrateto consumers based on (1) the initialchemical composition of the material, (2)the time of decay, and (3) the externalenvironmental conditions. Mangroves andsalt-marsh plants are recalcitrantsubstrates with low nitrogen content, andrequire extensive microbial growth andprocessing growth to become nutritionallyuseful. For many organisms, macroalgaeand epiphytes are useful substratesdirectly or with little microbial

addition. Seagrasses occupy a range fromthe middle of the spectrum to oneoverlapping with algae, depending onregion and environmental conditions. Inthe tropics, they are a high-proteinsource that encourages microbialutilization of the nutrients contained inthe seagrass substrate. In more temperatelocations, they may be a lower qualityprotein source and require more extensivemicrobial processing to become a usefulfood. In regions of high nutrientloadings, the seagrasses may develop anextensive epiphytic growth that may bemore productive and a less refractory foodsource than the seagrasses themselves, butthis level of epiphytism is not seen inclear, nutrient-poor waters.

76

CHAPTER 6. INTERFACES WITH OTHER SYSTEMS

6.1 SALT MARSH AND MANGROVE

In addition to the seagrass meadows, thewest coast of Florida has extensive marshand mangrove resources. West Floridaclaims 9% of the 6 million acres of marshbordering the Gulf of Mexico (Linda11 andSaloman 1977, Thayer and Ustach 1981>, butover 85% of the mangroves bordering thegulf (Thayer and Ustach 1981). In someareas, these habitats form only small,narrow fringes around the estuary, whilein other areas they extend many kilometersinland.

Like the seagrasses of Florida Bay, avast quantity of the Florida marsh andmangroves are contained within EvergladesNational Park (Table 16). Moving

northward from the vicinity of CharlotteHarbor on the lower west coast, the amountof mangrove coverage declines withincreasing latitude until near SuwanneeSound, north of Tampa, where mangroves arecompletely replaced by coastal marshes.Salt-marsh development is particularlyextensive from Apalachicola Bay eastward.Here, in the Big Bend region, the marshesextend from landward directly into theGulf of Mexico without any form ofprotective barrier. I n addition tomarshes of smooth cordgrass, Spartinaalterniflora, the Big Bend area hasextensive marshes of black needlerush,Juncus roemerianus.Florida

While the typicalsalt marsh shows Spartina

occupying the low marsh, and Juncus theregion landward (Figure 21), throughout

Table 16. The areas and major species of submerged vegetation, tidalmarsh, and mangrove swamps of estuarine study areas, west coast ofFlorida (from McNulty et al. 1972).

Study areaSubmerged Emergent vegetationvegetation Tidal marsh Mangrove

Acres Acres Acres

Florida bay . . . . . . . . . . . . . . 256,609Lake Ingraham . . . . . . . . . .._ 1,024Whitewater Bay . . . . . . . . . . . 155Cape Sable to

12,148 36,8970 891

68,757 75,976

Lostmans River . . . . . . . . .Lostmans River to

Mormon Key . . . . . . . . . . . . .Mormon Key to

789

768

108,644 49,349

23,840 36,000

Caxambas Pass . . . . . . . . . . 4,319Caxambas Pass to

52,181 92,385

Gordon River . . . . . . . . . . . 501 7,445 13,387

(Continued)

77

Table 16. (Concluded).

Study areaSubmerged Emergent vegetationvegetation Tidal marsh Mangrove

Doctors Pass toEster0 Pass ............

Caloosahatchee River .....Pine Island Sound ........Charlotte Harbor .........Lemon Bay ................Sarasota Bay System ......Tampa Bay .I..:..Hillsborough BayOld Tampa Bay . . .Boca Ciega Bay . .St. Joseph SoundBaileys Bluff to

Saddle Key . . . .Saddle Key to

S. Mangrove PtWaccassa Bay . . . .Suwannee Sound . .

.........

.........

.........

.........

.........

.........

.........

.........

.........Suwannee Sound toDeadman Bay ............

Deadman Bay ..............Deadman Bay to

St. Marks River ........Apalachee Bay ............St. George Sound .........Apalachicola Bay .........St. Joseph Bay ...........St. Andrew Sound .........East Bay (St. Andrew) ....St. Andrew Bay ...........West Bay .................North Bay ................Choctawatche Bay .........Santa Rosa Sound .........East Bay (Pensacola) .....Escambia Bay .............Pensacola Bay ............Perdido Bay ..............

Total . . . . . . . .._........ 523,431 528,328 392,860

Acres Acres Acres

11 2,959 9,720726 1,698 2,973

26,966 7,476 18,65723,383 9,087 23,4742,145 331 9717,610 235 3,6167,890 843 8,949

383 203 1,0776,809 533 5,0245,800 149 2,4648,723 608 1,259

4,084 16,683 1,301

62,730 32,587 7,91524,223 30,752 4485,556 17,643 427

2,420 14,763 01,834 2,549 0

8,110 14,325 023,521 55,669 08,641 3,605 0

737 17,696 06,325 853 0

373 576 01,146 4,597 02,540 875 01,542 3,349 01,030 1,664 03,092 2,816 04,683 309 0

310 3,307 043 5,152 0

1,547 213 01,333 1,408 0

78

MHW (Mean high water)_-----

Figure 21. Zonation in Florida salt marsh dominated by Spartina alterniflora and Juncos roemerianUS (fromDarovec et al. 1975).

much of the Big Bend area, Juncus willactually form the land-sea i n t e r f a c ewithout an intermediate Spartina zone(Carlton 1977; Stout 1984).

The importance of wetlands habitat tothe estuary has been established in avariety of locations (Odum and Heald 1972,1975; Thayer et al. 1978a; Thayer andUstach 1981; Odum et al. 1982), but thefauna1 interactions between these habitatsand adjacent seagrass beds are poorlyunderstood. Thayer and Ustach (1981)concluded that "although extensiveinformation exists on tidal marsh andmangrove plant species structure anddistribution in the gulf and on commercialspecies such as shrimp, quantitativestudies on the distribution and abundanceof submergent plants and on wetland faunaand fishes are scarce."

In particular, it is not known how thefaunas of the various areas interact, norwhat role the respective habitats play inthe life histories of the organisms.Fishes and invertebrates congregate withinthe mangrove prop roots for protection andshelter similar to the manner in which theseagrass canopy can provide nurseryshelter. Gray snapper, Lutjanus griseus,sheepshead, Archosargus probatocephalus,spotted seatrout, Cynoscion nebulasus, andthe red drum. Sciaenoes ocellatus. have

been found to recruit initially inseagrass habitat but with growth move intothe mangrove habitat for the next severalyears (Heald and Odum 1970). Since bothareas serve as nursery grounds foruncounted small organisms, both alsoprovide feeding grounds for largerpredators. Some of the game fish that arefound both in mangroves and seagrass bedsinclude the tarpon, Megalops atlanticus,the snook, Centropomus undecimalis, theladyfish, Elops saurus, the crevalle jack,Caranx hippos, the gafftopsail catfish,Bagre marinus, and the jewfish,Epinephelus itajara, (Heald and Odum1970). While similar interrelationshipsundoubtedly exist between certain fauna ofthe seagrass beds and salt marshes, theseare not documented. figure 22, from Lewiset al. (1985b), shows the life history oftwo of the most important fishes on thewest Florida coast. For a detailed reviewof the mangrove ecosystems of Florida, andtheir necessity to fishery organisms, seeOdum et al. (1982) and Lewis et al.(1985b), while Stout (1984) reviews theirregularly flooded marshes of thenortheastern Gulf of Mexico.

6.2 GULF REEFS

One of thestructuring of

79

major influences on theseagrass communities along

SPOTTED SEA TROUT.,.;,. .,.;;,.M a n g r o v e s ,._.. :.:<:.:.:.:.:‘.‘,‘,‘.‘.‘.‘.‘.‘.

* ,..........‘.‘,‘.‘,‘. :.:.:.:.:* ^ ^.:;:;:,‘,‘,:,:.~,‘:1 ^ .~:.I..

AA..,. A . 1

Figure 22. Life histories of spotted sea trout and snook on the west Florida COaSt(after Lewis et al. 1985b).

80

the gulf coast of Florida, when comparedwith the south Florida grass beds, is thelack of shallow coral reefs in closeproximity to the seagrasses. While not asintensely studied, the Big Bend area hasnumerous and extensive limestone outcropswhich should function in an analogousmanner. In the coral reef areas the mostprominent reef-grass bed interactioninvolves nocturnally active coral reeffishes of several families feeding overgrass beds at night. Randall (1963) notedthat grunts and snappers were so abundanton some isolated patch reefs in theFlorida Keys that it was obvious that thereefs could not possibly provide food oreven shelter for all of them. The majorgroups that shelter on the reef by day andforage into the seagrass beds nocturnallyare members of the Pomadasyidae,Lutjanidae, and Holocentridae (Longley andHildebrand 1941; Starck and Davis 1966).Typically, both juveniles and adults formlarge heterotypic resting schools overprominent coral heads or find shelter incaves and crevices of the reef. At duskthese fishes migrate (Ogden and Ehrlich1977; MacFarland et al. 1979) intoadjacent seagrass beds and sand flatswhere they feed on available invertebrates(Randall 1967, 1968), returning to thereef at dawn. These fishes epitomize whatKikuchi and Peres (1977) have defined as"temporal visitors" to the grass bed,utilizing it as a feeding ground (Hobson1973).

6.3 CONTINENTALSHELF

The ecology of all shallow watercommunities on the west coast of Floridais strongly influenced by the enormouscontinental shelf in the region,encompassing more than 78,000 km2. Theextremely low gradient in this region isresponsible for seagrasses being found atwhat would normally be great distancesoffshore. Throughout the region there aregradual fauna1 changes that occur both ona north-south gradient along the shore,and along a depth gradient offshore.

Along the latitudinal gradient, thefauna of the shallow water communitieschanges from a predominantly tropical WestIndian fauna in the south to a morewarm-temperate continental fauna with

Carolinian affinities in the north (Smith1976; Lyons 1979). This change isprimarily related to the decreasing wintertemperatures with the northwardprogression.

Moving from the shoreline to the edge ofthe shelf, several zones of fauna1similarity are recognizable, controlledlargely by changes in the physicalcharacteristics of the water column andthe substrate. This zonation is based onthe classification developed by Lyons andCollard (1974) and Lyons (1979). Thenearshore zone extends from the beachlineout to 10 m (Figure 23). This area iseither carpeted with seagrasses or has asediment of quartz sand in which theseagrasses are not found. Salinities varyfrom 31 to 34 ppt and temperatures varywidely over the year due to theshallowness of the water. Lyons (1979)characterized the fauna as being a "rich,warm-temperate fauna with obviousrelationship to the estuary."

The next zone seaward, the shallow shelfzone, extends to approximately 30- 40 m indepth, and while salinities are slightlyhigher and more constant, in the range of35-36 ppt, the temperatures in the greencoastal water are still seasonallyvariable. Where they exist, the sedimentsare calcareous, and the area also hasnumerous scattered outcrops of thelimestone bedrock, which provide substrateand shelter for many organisms, especiallyshallow water tropical species (Lyons1979). Near the outer edge of this zone,the clear blue offshore waters are foundwith nearly constant salinities andtemperatures that vary only 3 to 4 degreesseasonally. This is the middle shelfzone, extending down to about 140 m,although it has been previously dividedinto inner and outer subzones at 60-70 m(Lyons and Collard 1974). The sedimentsin this area are calcareous and thelimestone outcrops often extensive. Thefauna is primarily tropically derived(Lyons 1979).

Near the junction of the shallow andmiddle shelf zones southeast of Cape SanBlas lies a rich, rocky reef area known asthe Florida Middle Ground, a 1500 km2 areawith a mixture of irregular limestoneescarpments and knolls that rise as much

81

MISSISSIPPI -ALABAMA SHELF \ \\,\

W E S T F L O R I D A SHEL~F

0.10m

IO-30m

IO-60m

M d d l e she If !I

E D e e p sh,lf

6 0 1 4 0 m

140.200m

r--J S l o p e 200 -2ooo+m

Figure 23. Fauna1 zonation of the west Florida shelf (after Lyons and Collard 1974).

as 10 to 15 m from the shell and sandsubstrate (Smith et al. 1975). The highlytropical fauna of the area ischaracterized by corals of the generaPorites and Oculina, and the hydrocoralMillipora, along with otherscleractineans, alcxonarians,actiniarians, and zoantharians (Smith etal. 1975). In addition, benthic algae(Cheney and Dyer 1974), invertebrate(Austin 1970; Smith et al 1975), and fish(Smith et al. 1975) communities have beenfound to be highly tropical incomposition.

The distribution of tropical reeforganisms along the northwestern Floridashelf is a function of the highlyirregular, shallow shelf-bottom topographyand the influence of warm water masses.

Inshore circulation is dominated by twolarge gyres (Figure 24), with elements ofFlorida estuarine waters in the north,Florida Bay waters in the south, andtropical waters from the Loop Current,brought in from the Yucutan Channel (Chew1955; Austin 1970), which has thepotential for transporting large numbersof tropical larvae into the region (Smith1976). There is also evidence forseasonal upwelling along the outer edge ofthe Middle Ground (Austin 1970), whichSmith (1976) attributes as the reason forthe large numbers of planktivorous fishesin the region.

Throughout south Florida and in otherareas, more and more studies are showingthe interactions between the faunas of thereefs and the seagrass meadows, as well

82

Figure 24. Eastern Gulf of Mexico current patternsduring summer (after Chew 1955 and Austin 1970).

as with mangroves and coastal marshes(Ogden and Gladfelter 1983). Such studiesfor the seagrass meadows and the offshorereef and shelf fauna of the west Floridacoast are lacking, but the potential forthese fauna1 interactions is high (Darnelland Soniat 1979).

6.4 EXPORT OF SEAGRASS

One potentially important interaction ofthe west-coast seagrass beds and theoffshore communities is the transport ofdetached seagrass leaves and particulatematerial from the highly productiveinshore beds to the offshore areas. Thematerial exported from the seagrassmeadows can serve as both a carbon andnitrogen source for benthic, midwater, andsurface feeding organisms at considerabledistances from the original source of itsformation (Zieman et al. 1979; Wolff1980). In south Florida, the prevailingwinds move detached blades westward fromthe shallow grass flats. This material iscarried in considerable density over theproductive Tortugas shrimping grounds andhas been observed nearly 400 km west ofthe source beds (Zieman, unpubl. data).Incze and Roman (1983) found that

particulate organic carbon, largely ofbenthic macrophyte origin, accumulated inBiscayne Bay during the calm summer monthsand was then discharged followingresuspension by the cold fronts andaccompanying turbulence at the onset ofthe winter season.

Other studies have shown that seagrassescan be transported great distances fromtheir sources. Menzies et al. (1967)collected Thalassia leaves andoff the coast of North Carolinaof water, although the nearestThalassia was 1,000 km south.Brundage (1972) found blades of

fragmentsin 3,160 msource ofRoper andThalassiaof 5,000and Syringodium in nearly all

bottom ohotoaraohs taken in the VirainIslands 'basin-at' depths averaging 3,500-m.Wolff (1976) collected seagrasses,primarily Thalassia, from trenches in theCaribbean as deep as 6,740 m. Much of thematerial showed bite marks of shallowwater parrotfish as well as indications ofrecent consumption.

Grazing by herbivores, mortality causedby low tides on shallow banks, andwave-induced severing of leaves that arebecoming senescent are the primary sourcesof drift material. Sporadic largereleases of material occur during majorstorms, in which both living leaves andrhizomes are uprooted (Thomas et al.1961).

For all species of seagrasses, bladesthat are fresh and healthy when detachedwill float better than senescent leaves.Because of the difference in size andshape of Thalassia and Syringodium blades,grazing or nibbling by most herbivoreswill completely sever a Syringodium bladeand allow it to float off, while the samebite will not sever a Thalassia blade(Zieman et al. 1979). In addition.Syringodium blades float better than thoseof Thalassia. so that a much hiaherproportion of' the Syringodium producgionis transported from the source bed. InSt. Croix, 60%-100% o f the dailyproduction of Syringodium was detached andexported, whereas only 1% of Thalassia wasexported, primarily as bedload (Zieman etal. 1979). In the Indian River, Fry(1984) found that 47% of the Syringodiumproduction was transoorted from thesystem, which, in part,' could account for

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the absence of seagrass isotopic signaturein the consumers there. No studies as yetexist on the export or transport ofseagrass material from the meadows of thewest Florida coast; however, because ofthe demonstrated importance in otherFlorida seagrass beds, it is likely thatthere is a large amount of materialtransported from this region. Itsdestination and fate, however, remain tobe quantified.

6.5 NURSERY GROUNDS

One of the most important roles ofseagrass beds in the coastal ecosystem isthat of a nursery ground in whichpostlarval stages of fishes andinvertebrates concentrate and develop. Inaddition, important species, such as thespotted seatrout, Cynoscion nebulosus,spawn in, or just adjacent to, seagrassbeds (Tabb 1966a,b; Lassuy 1983).Seagrass habitats offer high productivity,surface areas, and blade densities, aswell as a rich and varied fauna and flora.Seagrass provides abundant nursery habitatand, based on abundance and size data,many important species prefer it overavailable alternatives in the estuariesand coastal lagoons (Yokel 1975a). InApalachicola Bay, Livingston (1984) notedthat numerous invertebrates and fishesused the seagrass beds as nurseries. Mostof the penaeid shrimp and fishes found inthe beds were seasonally abundant duringearly stages of their reproductive cycles(Livingston 1984b).

Numerous species of fishes andinvertebrates have been found to useFlorida grass beds as nursery grounds. InTampa Bay, 23 species of finfish, crab,and shrimp, of major importance in Gulf ofMexico fisheries, were found as immatureforms (Sykes and Finucane 1966).Livingston (1984) found Apalachicola Bayto be an important nursery for numerousinvertebrates and fishes, and listed theabundance, natural history, andseasonality of 26 of the most importantspecies (Table 17 in Livingston 1984b). Athird of the species collected atMatecumbe Key seagrass beds by Springerand McErlean (1962), including all grunts,snappers, filefishes, and parrot fishes,occurred only as young, indicating the

8

nursery value of the seagrass-dominatedshoreline habitat sampled.

6.5.1 Blue Crabs

The blue crab, Callinectes sapidus, isan abundant and important resource alongthe gulf coast for both sport andcommercial fisheries, ranking as the thirdlargest food fishery in the Gulf of Mexico(Perry 1975; Oesterling and Evink 1977).Blue crabs are caught throughout Florida,but are in lowest abundance in the FloridaKeys and reach their highest abundance inthe area between Tampa and ApalachicolaBay (Steele 1979). Like nearly all of thefishery resources of the gulf coast, bluecrabs are estuarine dependent throughoutmuch of their life.

Following spawning, the young crablarvae drift with the currents andmetamorphose into a megalops stage. Theyoung crabs enter the estuary either asmegalopi or as early juveniles, using aform of tidal migration, burying in thesediments on the ebb tide and rising intothe water column to be transported intothe estuary on the flood tide (Williams1971; Sulkin 1974), a mechanism firstproposed for pink shrimp larvalmigrations. In the estuary they grow andmature, using the seagrass meadows asnurseries during their juvenile stages.Mature crabs are found throughout theestuary, with many continuing to forage inthe seagrass beds. When mature, thefemales will move into lower salinitywaters and protected areas such as tidalcreeks, molt a final time, and breed whilestill soft (Oesterling and Evink 1977).The females cannot molt once fertilized.After hardening and as their egg massesdevelop, the females begin to migrateoffshore to higher salinity waters. Theadult males generally remain within theestuary and continue to grow.

The typical patterns described for bluecrab spawning indicate that the femalesmove offshore and spawn in the generalvicinity of their source estuary.However, tagging studies in Florida haveshown that females migrate extensivedistances, up to 500 km, to spawn in theApalachicola Bay region (Oesterling andEvink 1977). Following spawning, theplanktonic larvae become entrained in eddy

4

currents related to the Loop Current andthe two inshore gyres, and are distributedalong the coast of Florida (Figure 25).The losses with this type of reproductionare apparent; it has been estimated thatonly one millionth of the spawn reachmaturity (Van Engel 1958). The migrationof the female crabs coincides with theflooding of the Apalachicola and adjacentriver systems, which is thought toincrease the amount of suspendedparticulate detritus and aid in providingfood for the larvae and juvenile crabs(Oesterling and Evink 1977; Livingston1984b). Oesterling and Evink (1977) andLivingston (1984b) correctly pointed outthat current plans by the Army Corps ofEngineers to place additional dams in theApalachicola drainage basin ostensiblyfor flood control and navigation, could bedisastrous to this vital fishery.Likewise, the diversion of fresh waterflow for additional development could havesimilar deleterious effects.

6.5.2 Shrimp

Penaeid shrimp are an important fisheryresource in Florida, especially in thegulf coast region. While the menhadenfishery is the largest in the Gulf ofMexico in terms of pounds landed, the

Figure 25. Blue crab spawning migrations and larvaltransport (after Oesterling and Evink 1977).

shrimp fishery is the largest in dollarvalue (Taylor et al. 1973b). The twomajor shrimping grounds are the Tortugasgrounds to the north and west of the DryTortugas, and the Sanibel grounds,stretching from just north of Naples tosouth of Tampa (Saloman et al. 1968). Thenurseries for this fishery are in theseagrass beds, mangroves, and marshes ofcoastal Florida (Tabb et al. 1962,Costello and Allen 1966). The shrimpspawn on the fishing grounds in deeperwater throughout much of the year, and thelarvae are carried back into the coastalwetlands (Tabb et al. 1962; Munro et al.1968). Roessler and Rehrer (1971) foundpost-larval pink shrimp entering theestuaries of Everglades National Park inall months of the year.

Throughout Florida, the most copiouspenaeid is the pink shrimp, Penaeusduorarum. South of Tampa, individuals ofthe brown shrimp, Penaeus aztecus, and theCaribbean white shrimp, Penaeusbrasieliensis, are found intermixed withthe pink shrimp, but are usually notabundant (Saloman et al. 1968). North ofTampa: the pink shrimp is the mostplentiful, being the seventh to ninth mostabundant invertebrate in Apalachee Bay,while individuals of the white shrimp,Penaeus setiferus, occupy the same habitatbut are not numerous in this area (Hookset al. 1976; Dugan and Livingston 1982).Moving westward from Florida, the pinkshrimp catch decreases and the brown andwhite shrimp catches increase greatly.

Studies throughout south-west Floridaestuaries in Rookery Bay, Marco Island,and Fakahatchee Bay have shown that theshrimp were most abundant at stations withseagrass-covered bottoms, and within thesestations, where benthic vegetation wasdense (Yokel 1975a, 1975b). Post-larvalshrimp with carapace lengths less than 3mm were taken only at stations whereHalodule and Thalassia were present inRookery Bay Sanctuary, while stationswithout grass always had larger meansizes. The smallest shrimp arecontinuously within the seagrass bed. Asthey increase in size and become too largeto burrow between the seagrass shortshoots, they tunnel by day in adjacentsand flats and forage in the grass bed atnight. As they near maturity, they

a5

migrate to the deeper waters offshore,usually at the onset of the first majorcold front passage of the season(Hildebrand 1955, Williams 1965). Recentstudies using stable isotope tracers haveshown populations from two contiguousbodies of water, Rookery Bay and JohnsonBay, to have distinct isotopic signatureswhich take weeks to months to acquire.This indicates that the populationsare staying within their embayment, andare not moving freely throughout thehabitat of the region (Zieman et al.1984c).

6.5.3 Fish

Like those in south Florida (Zieman1982), the seagrass beds of the westFlorida coast are important nurserygrounds tor numerous species of commercialand sportfish, and for small foragespecies that serve as food for largercarnivores. While the composition of thegrassbeds of the Florida Keys and portionsof Florida Bay are distinct because of theinfluence of reef-related juveniles, thefauna from northwestern Florida Bay ishighly similar to all the inshore regionsof the west coast to Apalachicola Bay,both in terms of the important familiesand the numerically most abundant species.The major families containing predatorsthat are associated with seagrass beds atsome stage in their life cycle are theSparidae, Sciaenidae, Pomadasyidae,Sygnathidae, Balistidae, and Serranidae(Joseph and Yerger 1956; Springer andWoodburn 1960; Tabb and Manning 1961; Wangand Raney 1971; Mountain 1972; Yokel1975a; Livingston 1984a).

In virtually every survey of fish faunaof the west coast of Florida, the pinfishwas the most abundant fish collected, and

nearly all abundanti:roughout the year.c?~e~ook~~~ Bay (Yokel1975a) and in Fakahatchee Bay (Yokel1975b) on the southwest Florida coast,juvenile pinfish showed a strongpreference for vegetated areas. Thesheepshead, another sparid, initiallyemigrates to grass beds but quickly movesinto mangrove habitats (Heald and Odum1970) or rocks and pilings (Hildebrand andCable 1938). The spottail pinfish,Diplodus holbrooki, and‘the gras; porgy;Calamus arctifrons, are other common but

much less numerous sparids that frequentgrassbeds in this region.

Several sciaenid species may be found inthe grassbeds of west Florida, but themost common are the spotted seatrout, thespot, and the silver perch. The spottedseatrout is one of the few largercarnivorous fishes present in southFlorida waters to spawn within the estuary(Tabb 1961, 1966). Its eggs sink to thebottom and hatching takes place in bottomvegetation or debris (Tabb 1966). Thesilver perch is the most abundant sciaenid(often second to the pinfish) in northernFlorida and Whitewater Bays, being takenthroughout the year (Tabb and Manning1961).

The pigfish is the most common pomo-dasyid, inhabiting areas with grassy ormuddy bottoms and turbid water in westFlorida estuaries. The white grunt isless abundant, but is common throughoutthe area, occurring most commonly overThalassia beds in clear water as juveniles(Tabb and Manning 1961; Roessler 1965;Bader and Roessler 1971; Weinstein andHeck 1979).

The two snappers (Lutjanidae) that aremost common throughout the region are thetwo most often associated with grassbeds,the gray snapper and the Lane snapper.Both occur throughout the range, and areespecially common in south Florida.Juvenile gray snappers have beenconsidered the most common snapper innorthern Florida and Whitewater Bays,including freshwater regions (Tabb andManning 1961), while juvenile Lanesnappers have been abundant in Thalassiahabitat in northern Florida Bay whensalinities were above 30 ppt (Tabb et al.1962) in northern Florida Bay, and werethe most common snapper taken in grasshabitat of the Ten Thousand Island regionof the southwestern Florida coast (Yokel1975a,b; Weinstein et al. 1977; Weinsteinand Heck 1979).

6.5.4 Detached Macrophytes asNursery Habitat

In the previous chapter, it was notedthat even using such a coarse samplingdevice as a large mesh otter trawl willyield many small organisms, such as

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amphipods and isopods (see Chapter 5), aswell as numerous juveniles which usedetached macrophytes as shelter. Althoughseagrasses may be associated with thesemateriais, it is primarily composed of1 drge balls or amorphous masses ofdrifting algae (Cowper 1978). While manyalgae can go into the makeup of the driftalgae, the most common ones in western andsotithern Florida are species of therhodophyte genus Laurencia.

Currently, there are few studies of thishighly important but ephemeral habitat.In western Australia, Lenanton et al.(1982) showed that the concentrations ofseveral important fish were highest in thezone of the drift algae near the shore.The main food of these fishes wereamphipods that were profuse in the driftalgae. In addition, the arrival of the

juveniles appeared to correspond with thegreatest accumulations of the drift algae.

While seagrass beds may be importanthabitat for pre-adult and immature adultspiny lobsters, Panulirus argus, in southFlorida, drift algae have been found to bea critical habitat for the newly settledjuvenile lobsters (Marx and Herrnkind1985). The earliest stages of lobsterswere found solitarily occupying clumps ofLaurencia, using it for shelter andabundant food. After reachingapproximately 17 mm in carapace length,the juvenile lobsters leave their solitaryexistence in the drift algae and begin toaccumulate in dens, becoming moregregarious with the transition (Marx andHerrnkind 1985). Although other studiesare lacking at this time, drift algae isan associated habitat of potentially greatimportance as a nursery and needs muchmore study.

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CHAPTER 7. HUMAN IMPACTS AND APPLIED ECOLOGY

The west coast of Florida possesses vastregions of highly productive coastal sea-grass, mangrove, and marsh habitats thatcontinue to be relatively undisturbed byhuman impact. This same region also hasareas like Tampa Bay that could serve ascase studies on how to rape and plunder aformerly productive natural system withutterly no concern for the future. Whilesome forms of human impact, such as oilspills, have less impact on seagrassmeadows than on the emergent interfacecommunities (mangroves and salt marshes),other stresses, especially dredging,filling, and eutrophication are highlydestructive to the seagrasses. Heavypopulation influx and the resultingdevelopmental pressures have severelyimpacted some areas, but others, such asthe Big Bend area, have been lessthreatened due to their relatively lowpopulation density, inacessibility! andrecent conservation efforts. In addition,while all of Florida's coastal waters nowhave increased protection, Rookery Bay,Apalachicola Bay, and much of CharlotteHarbor and Pine Island Sound have now beenmade estuarine sanctuaries and marinepreserves.

termed acute stress as opposed to chronicstress. Acute stress is stress resultingfrom direct damage that physically killsor removes the plants. The most commonexample of this type is the extensivelosses that have been caused by directhabitat removal by dredging and filling.By comparison, chronic stress graduallykills the plants over a period of time,creating conditions in which eitherrespiration exceeds production or in whichthe plants lose their ability to competewith other species for light, nutrients,and space. Two of the major causes ofthis type of stress are eutrophication,with its excessive algal growth, and thesuspended sediments and nutrients fromdredging and filling operations. Both ofthese causes of pollution operate in asimilar manner on the seagrasses; that is,they increase turbidity and decrease thelight incident on the seagrass leaf,reducing its net production andcompetitive fitness.

Many publications now document theecological importance of these habitatsand the extent of human impact, bothpotential and realized, upon them (Zieman1975b, 1982; Thayer et al. 1975, 1984a;Phillips 1978; Ferguson et al. 1980;Livingston 1984a; Zieman et al. 1984c).

Most of the recorded seagrass losseshave been attributed to acute stresseffects. However, this may simply be dueto the easier accountability when a brief,obvious stress, such as a canal dredging,destroys a grass bed. The great lossesthat are now being documented for many ofFlorida's estuaries have been caused bythe insidious, continual decline of waterquality in these estuaries.

19:;)previous reviews (Zieman 1975b,

humanbased' on

impacts were categorizedthe activity causing the

damage. This study adopts a somewhat morefunctionally based approach. Seagrassescan be killed off by human impacts, or insome cases natural disturbances, eitherdirectly or indirectly, by what will be

7.1 DREDGING, FILLING, AND OTHERPHYSICAL DAMAGE

7.1.1 Acute Stress

The most common and obvious destructiveinfluence on seagrass beds in Florida hashistorically been the dredging and fillingof estuaries and adjacent wetlands.

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I

Florida ranks third among the gulf coastStates, after Texas and Louisiana, inamount of submerged land that has beenfilled by dredge spoil with 9,520 ha(Linda11 and Saloman 1977). In Texas andLouisiana, most of the spoil created camefrom dredged navigation channels, while inFlorida, it accounts for less than 5% ofthe State total (Figure 26). Notsurprisingly, the majority of filling ofsubmerged areas in Florida has been tocreate land for residential and industrialdevelopment.

Studies conducted in Tampa Bay and BocaCiega Bay were among the first todemonstrate the long-term impact ofdredging activities, and remain some ofthe most definitive. Between 1950 and1968, an estimated 1,400 ha of the baywere filled during projects involving theconstruction of causeways and the creationof new waterfront homesites (Figure 27).In undisturbed areas of the bay, luxuriantseagrasses grew in stable sedimentsaveraging 94% sand and shell. At thebottom of dredged canals the unvegetatedsediments averaged 92% silt and clay(Taylor and Saloman 1968). While severalstudies of Boca Ciega Bay collectivelydescribed nearly 700 species of plants andanimals occurring there, Taylor and

Figure 26. Channel through grassbed withopen-water dredge disposal area in Tampa Bay (photoby R. R. Lewis).

Saloman (1968) found only 20% of thosesame species in the canals. Most of thosewere fish which are highly mobile and thusnot restricted to the canals durinqextreme conditions. Species numbers werehigher in undisturbed areas, but 30% morefish were found in the canals. The mostabundant (the bay anchovy, the Cubananchovy, and the scaled sardine), areplanktivorous, and may have benefittedfrom the higher nutrient levels in thecanals and the shelter provided.Recolonization was negligible at thebottom of the canals and it was concludedthat the sediments there were unsuitablefor most of the bay's benthic inverte-brates. Light transmission values werehighest in the open bay away from land-fills, lowest near the filled areas, andincreased somewhat in the quiescent watersof the canals. Due to the depth of thecanals, however, light at the bottom wasinsufficient for seagrass growth. Taylorand Saloman (1968), using conservative andincomplete data, estimated that filloperations in the bay resulted in a nannual loss of $1.4 million for fisheriesand recreation.

At the time these canals were built,developers dredged them as deep aspossible to produce cheap fill materiallocally, frequently to depths of 5-8 m inareas where the original water depth wasonly 1 m or less. Combined with theeasily suspended sediments, thisrelatively great depth and the shadingeffects of the vertical canal wallsprevented the regrowth of productiveseagrasses. The depth and the shallowsill near the opening caused them tobecome stagnant, organic traps with highlyreducing sediments that were easilydisturbed. When storm action resuspendsthese sediments, the water column canquickly become anoxic, causing localizedmortality. Many of these problems derealleviated in recent years when permittingof deep canals was curtailed.

Burial of seagrasses can be asdestructive as dredging; however, ifseagrasses are only lightly covered andthe rhizome system is not damaged,regrowth through the sediment is sometimespossible. Thorhaug et al. (1973) foundthat construction of a canal in Card Soundtemporarily covered turtle grass in an

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area of 2-3 ha with up to 10 cm ofsediment, killing the leaves, but not therhizome system. Regrowth occurred whenthe dredging operatLions ceased and.currents carried the sediment away.

7.1.2 Other Physical Damage

Any physical damage to the sediments andrhizome structure of seagrass beds canhave long-term effects, no matter howinsignificant the damage may seemvisually. Small cuts, no more than 10 cmwide and a similar depth in the sediments,from the propellers of the innumerableoutboard boats crossing Florida seagrassbeds, can take from 3 to 5 years torecover in a Thalassia bed (Zieman 1976).

Damage by larger boats can be vastlymore severe and long lasting. During theconstruction of the new bridges in theFlorida Keys, a contractor attempted tocut transit time barging new bridge

Figure 27. Dredged and filled areas in Boca Ciega Bay (photo by M. J. Durako).

sections into the Niles Channel bridge.Instead of using the deep water access onthe Atlantic side, the contractor used alarge tugboat to prop-dredge a new passagethrough a shallow Thalassia flat. Theresulting swath was several hundreds ofmeters in length, about 10 m in width, andup to 2 m in depth. This, in effect,created a new tidal pass, and with thehigh water velocities during tidal flowthrough it, it is doubtful that the cutwill ever return to normal. Fortunately,the federal courts determined that suchwanton distruction constituted illegaldredging and filling (Zieman, unpubl.data).

In estuaries near Tampa and TarponSprings, Godcharles (1971) found norecovery of ei,ther ThalassiaSyringodium in areas where commercii\;hydraulic clam dredges had severedrhizomes or uprooted the plants, althoughat one station recolonization of Halodulewas observed.

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7.1.3 Chronic Effects

In addition to the direct effect ofburial, secondary effects from turbidity,which restricts nearby productivity,chokes filter feeders by excessivesuspended matter, and depletes oxygen byrapid utilization of suspended organicmatter, can have serious consequences.The dredged sediments are unconsolidatedand readily resuspended. Thus, a spoilbank can serve as a source of excesssuspended matter for a protracted timeafter deposition.

In 1968, lush growths of Thalassia hadbeen recorded at depths UD to 10 m inLindberg Bay, in St. Thomas,'U.S.V.I., butby 1971 this species was restricted, byturbidity caused by dredging, to sparsepatches usually occurring in water 2.5 mdeep or less (Van Eepoel and Grigg 1970).Similar declines were observed by Grigg etal. (1971) in Brewers Bay, St. Thomas.

Odum (1963) found light penetration wasreduced in seagrass flats adjacent to thedredging site of an intracoastal waterwayin Redfish Bay, Texas. Subsequentdecreases in productivity of Thalassiawere attributed to the stress caused bysuspended silts. Growth increased thefollowing year and Odum attributed this tonutrients released from the dredgematerial. While dredging altered the 38 mlong channel and a 0.5 km zone of spoilisland and adjacent beds, in this instanceno permanent damage occurred to theseagrasses outside this area beyond thisregion.

7.2 EUTROPHICATIONANDSEWAGE

The greatest losses of seagrass habitatare caused by the effects of physicaldamage from dredging and the chronicstresses placed on the plants by suspendedsediments and eutrophic algal growth,manifested in the form of increasedturbidity and resultant light reduction.In many ways it is the most insidious formof pollution, for it usually appears as aslow and gradual worsening of local waterquality. With gradually increasingturbidity and decreasing water clarity, itis less noticeable that seagrasses are nolonger distributed as deep as they were

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previously, and the choking growths ofepiphytes are also less obvious. Thus,the natural communities are diminished andtheir valuable functions as habitat andshelter are either decreased or lostentirely.

Seagrass beds subjected to botheutrophication and suspended sediments inChristiansted Harbor, St. Croix, declinedand were replaced by the green alga,Enteromorpha, reducing the area1 extent ofthe seagrasses by 66% over a 17-yearperiod (Dong et al. 1972). InHillsborough Bay, phytoplanktonproductivity increased due to nutrientenrichment from domestic sewage andphosphate mining discharges (Taylor et al.1973b). Phytoplankton blooms contributedto the problem of turbidity, which wasincreased to such a level that seagrassespersisted only in small, sparse patches.The only important macrophyte found in thebay was the red alga, Gracillaria. Softsediments in combination with low oxygenlevels limited diversity and abundance ofbenthic invertebrates (Taylor et al.1973b).

In northern Biscayne Bay, McNulty (1970)found few seagrasses in waters that werepolluted by sewage discharge in 1956.Within 1 km of the outfall only smallpatches of Halodule and Halophila werefound. Following the construction of anoffshore outfall, postabatement studies in1960 found that the seagrasses hadcontinued to decline, probably due to thepersistent resuspension of sediment from acauseway and other nearby constructionprojects. The fine sediments of this areaare highly prone to resuspension whenlacking the stabilizing influence of theseagrass canopy.

7.3 OIL

Increased demand for local petroleumsupplies has intensified exploration foroffshore sources in shallow continentalshelf, such as is found off the westFlorida coast. The potential for damageto local marine communities, as well asthose at some distance, is present at allstages of oil production, includingexploration, production, and transporta-tion, although not all of the risks are

equal. The National Academy of Sciences(NAS 1975) has found that the greatestrisks are associated with shipping acci-dents, followed by those spills associatedwith loading and unloading oil. Getter etal. (1980) noted that of 16 oil spills inthe Gulf of Mexico and Caribbean 75% weretransit accidents. By comparison, NAS(1975) estimates that about 1.3% of theannual input of oil to the oceans is theresult of drilling and production losses.On the west coast of Florida, the remain-ing seagrasses of busy ports like Tampa,as well as the beds of South Florida,would seem to be the most vulnerable todamage from oil spills. The large beds ofthe Big Bend region are deeper and wellremoved from major shipping lanes. Theknown effects of oil spills, cleanup pro-cedures, and restoration on seagrasscommunities and associated organisms werereviewed by Zieman et al. (1984b).

Petroleum products can damage seagrassecosystems in a variety of ways. Thesehave been summarized by Blumer (1971),Cintron et al. (1981), and Zieman et al.(1984b) and include:

1. Direct mortality of organisms due tosmothering, fouling, and asphyxia-tion; poisoning by direct contactwith oil (especially fresh oil); andabsorption of toxic fractions fromthe water column.

2. Indirect mortality due to the deathof food sources or the destructionor removal of habitat.

3. Mortality of sensitive juvenileforms, especially those using thegrassbed as a nursery ground.

4. Incorporation of sublethal amountsof petroleum fractions into bodytissues, potentially loweringtolerance to other stresses.

5. Reduction or destruction of the foodor market value of fisheries due tothe tainting of flavor by absorptionof hydrocarbons, even though theamounts are sublethal.

6. Incorporation of potentially car-cinogenic or mutagenic substancesinto the food chain.

Although much more laboratory work isneeded, the few studies existing that havestudied the effects of petroleum productson seagrass community components haveshown them to be toxic to the organisms.Seagrasses exposed to low levels of watersuspensions of kerosene and toluene showedsignificantly reduced rates of carbonuptake (McRoy and Williams 1977).

Refined products have consistently beenfound to be more toxic to marine organismsthan crude oils. Larval stages of grassshrimp were slightly more resistant to theoil than the adults, while all forms ofthe oils were more toxic to the larval andjuvenile stages of white and brown shrimpthan to adults. Changes in temperatureand salinity, which are routine inestuaries, enhanced the toxic effects ofthe petroleum hydrocarbons (Anderson etal. 1974). The best indicator of oiltoxicity is probably the aromatichydrocarbon content of the oil (Andersonet al. 1974; Tatem et al. 1978).

Numerous studies have indicated thatintertidal communities are the mostvulnerable of all marine communities;thus, seagrass ecosystems are usually lessvulnerable due to their generally subtidalnature. There would seem to be adecreasing likelihood of damage withincreasing depth, so that grassbedsseveral meters or more in depth arepossibly better protected from oil spillsthan intertidal beds.

The impact on marine and estuarinecommunities, including seagrasscommunities, of several large-scale oilspills has been investigated but these areafter-the-fact damage assessments. Theresults were highly variable, ranging fromheavy destruction to little damage, afactor of the size of the spill andnumerous other variables in environmentalconditions. The case studies reviewed inZieman et al. (1984b) are among thebest-documented examples of oil spillsaffecting seagrass beds. In general,seagrasses suffered relatively littledamage because of the subtidal nature ofthe systems; the primary impact was on theassociated fauna1 communities. Those bedsthat were exposed to oil at low tide didnot suffer greatly, due in part to theirburied rhizome system.

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t

7.4 TEMPERATUREANDSALINITY

Because of the latitudinal variationalong the coast of west Florida, thermalpollution will have different effectsalong this gradient. At the southern end,the seasonal programming is tropical andmany organisms are growing near theirthermal maxima in the summer under normalconditions (Mayer 1914, 1918). At thenorthern end of the gradient, theseagrasses are at the northern limits intheir distribution and are more likely tobe restrained by winter minima. However,even in this region, summer temperaturesare high and areas with shallow water andrestricted circulation can becomeextremely hot in the summer.

The time of exposure to either extremehigh or low temperatures is critical inassessing the effect of thermal stress.Many organisms can tolerate large-amplitude temperature changes on ashort-term basis, but are intolerant ofchronic exposure to smaller changes.Seagrasses have buried rhizome systemsthat include the meristematic regions forleaf, root, and rhizome growth, and therelatively poor thermal conductivity ofthe sediments serves as an effectivebuffer against short-term temperaturedamage. Therefore, the seagrasses aremore resistant to brief high temperatureincreases than the commonly occurringalgae. Continued heating, however, canraise the sediment temperature to levelslethal to the plants (Zieman 1975). Theanimal components of the seagrass systemsshow the same ranges of thermal tolerancesas the plants. Sessile forms are moreaffected, being unable to escape eithershort-term acute effects or long-termchronic stresses.

The primary sources of human-inducedthermal stress in estuaries are thecooling systems of electrical power plants(Figure 28). In addition, some industrialplants produce waste heat, and, in somecases! heated wastewater that alsocontains a variety of waste chemicalproducts.

Damage to communities subjected to theseinfluences has been reported at variousstudy sites in Florida (Zieman and Wood1975; Thorhaug et al. 1978, Zieman 1982).

Figure 28. Crystal River power plant (photo by R. R.Lewis).

Effluent from the Bartow power plant nearthe mouth of Old Tampa Bay, which reacheda level of 7.2 'C above ambienttemperature, killed 81 ha of seagrasses(Blake et al. 1976). Where temperatureswere 2 OC above ambient or less, all ofthe local seagrass species survived, butat 3OC above ambient, only sparseHalodule survived. Several parameters ofHalodule were measured in the effluentplume and at a control station on theintake side of the plant. At the intakestation, the biomass varied from 5 to 10times greater than on the effluent side,while the length of the leaves andemergent short shoots on the intake sidewere over twice the length of leaves fromthe effluent side. During summers,blue-green algal mats covered a largeportion of the area where the temperaturewas greater than 3 "C above ambient (Blakeet al. 1976), a condition similar to thatfound at Turkey Point in south BiscayneBay (Zieman and Wood 1975).

In addition to the seagrasses, changeswere found in the associated animalcommunities in the effluent of the Bartowpower plant. On the intake side of theplant, 104 species of invertebrates wereidentified, primarily polychaetes,mollusks, crustaceans, and echinoderms,while on the effluent side only 60 species

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were found (Blake et al. 1976). Numbersof individual polychaetes were greater onthe effluent transects, crustaceannumbers were greater along the intaketransects, and mollusk numbers weresimilar in both areas (Blake et al. 1976).Virnstein (1977) found a decrease indensity and diversity of benthic infauna

theli-37

whereOC wzLzarsecorded.

temperatures of

On the west coast of Florida, effluentsfrom the Crystal River power plantimpacted shallow-water seagrass andmacroalgal communities, but because of thechanging nature of the studies over theyears, and particularly due to the highlyqualitative methods used in the earlysurveys, full assessment of the impactfrom thermal effluents is not possible.Numerous studies have shown a reduction inthe number of macroalgal species and theirabundance in the vicinity of the effluent(Steidinger and Van Breedveld 1971; VanTine 1981). In the most recent study,stations outside the area of the thermaleffects to the south showed greaterseagrass species diversity, biomass, andproductivity than those associated withthe thermal effluent (Stone and Webster1985). Sample stations north of thethermally-affected area showed patternssimilar to those near the effluent, butconditions at these stations proved to beinconsistent with the southern controlstations. They were in an area of reducedsalinities caused by the WithlacoocheeRiver and the western section of the CrossFlorida Barge Canal. Turbidity was highin this region due to the resuspension ofsediments from the abandoned barge canaland its spoil islands, thereby limitingits usefulness as a comparison area.

Barber and Behrens (1985) studied theeffects of the effluent of an oil-firedpower plant near Anclote Key, about 50 kmnorth of Tampa Bay, on the seasonalproductivity of Thalassia and Syringodium.Throughout the fall and winter months,both species showed greater productivityin the effluent than at the controlstation. As temperatures rose in thespring, the productivity increasedcomparably at all stations, ver.y rapidlyin March and April: Thalassiaproductivity at the thermally stressedstation was less than at the control

station except for a brief period at theend of the summer, which was notstatistically significant. Syringodiumproductivity at the thermally-effectedstation exceeded that of the controlstation in early May, but fellprecipitously at the end of the month.Barber and Behrens (1985) concluded thatthe heated effluents in this centralFlorida region had a positive effect onseagrass productivity, until it reachedthe upper optimal growth temperature foreach species was reached. Above thisupper thermal limit, productivitydeclined.

The response patterns to thermaleffluents seen in these west Floridaestuaries are similar to those previouslyreported in south Florida. As thetemperatures in south Biscayne Bay wereraised by the effluent of the Turkey Pointpower plant, the productivity, biomass,and area1 distribution of seagrassesdecreased along the path of the effluentplume of the power plant (Zieman and Wood1975). Increases in ambient temperatureof 4 OC or more killed nearly all faunaand flora present (Roessler and Zieman1969). A rise of 3 OC above ambientcaused both species numbers and diversityof algae to decrease. The optimaltemperature range for maximal speciesdiversity and numbers of individuals foranimals was between 26 and 30 OC;temperatures between 30 and 34 OC excluded50% of the invertebrates and fishes, andtemperatures between 35 and 37 OC excluded75% (Roessler 1971; Zieman and Wood 1975).

Throughout their range, Thalassiacommunities seem to show similar thermalresponse patterns. Thorhaug et al. (1978)collated and compared the response ofthese communities in the Caribbean tropics(Guyanilla Bay, Puerto Rico), subtropics(Biscayne Bay and Card Sound, Florida),and subtropical warm-temperate border(Tampa Bay). The summer mean temperaturesin all of the estuaries averaged about 30OC. Temperature elevations of 5 OCdestroyed and denuded the Thalassiameadows; elevations of 4 OC showed severedamage to all components of thecommunities. With a 3 OC temperatureelevation, damage was severe in the higherlatitudes and less in the more tropicalenvironments. Data was insufficient to

94

allow intercomparisons of lessertemperature elevations, but it was clearlyindicated that temperature elevations ofgreater than 3 OC above ambient in thewarmer months produced severe andsustained damage (Thorhaug et al. 1978).

While all of the local seagrass speciesare euryhaline to varying degrees,Thalassia and Syringodium show a decreasein photosynthetic rate as salinity dropsbelow full-strenqth seawater, whileHalodule is less affected (McMillan andMoselev 1967). The seasonalitv ofseagrasses in Florida is largely explainedby temperature and salinity effects(Zieman 1974; Barber and Behrens 1985).The greatest decline in plant populationswas found when combinations of hightemperature and low salinity occurredsimultaneously. The reduction of seagrassbiomass and productivity at one set ofstations near the Crystal River powerplant which were intended to serve ascontrols, was attributed to reducedsalinities emanating from the CrossFlorida Barge Canal and the WithlacoocheeRiver (Stone and Webster 1985).

While h$igher salinities may yieldsomewhat lusher and more productiveseagrass beds compared to those found inmesohaline waters, the intermediatesalinities seem to be most important forthe nursery function of the seagrassmeadows. Tabb et al. (1962) stated:"Most of the effects of man-made changeson plant and animal populations in Floridaestuaries (and in many particulars inestuaries in adjacent regions of the Gulfof Mexico and south Atlantic) are a resultof alterations in salinity and turbidity .. . . High salinities (30-40 ppt) favorthe survival of certain species like seatrout, redfish, and other marine fishes,and therefore improve angling for thesespecies. On the other hand these highersalinities reduce survival of the youngstages of such important species ascommercial penaeid shrimp, menhaden,oysters, and others. It seems clear thatthe balance favors the low to moderatesalinity situation over the high salinity.Therefore, control in southern estuariesshould be in the direction of maintainingthe supply of sufficient quantities offresh water which would result inestuarine salinities of 18 to 30 ppt."‘

7.5 PAPERMILLEFFLUENTS

Throughout the gulf coast region, withits enormous timber resources, there arenumerous paper mills discharging hugequantities of waste materials into rivers,which almost immediately wash thismaterial into the nearby estuaries.Through numerous publications, Livingston(1975, 1984a, 1987) has chronicled thechanges in the seagrass communities due tokraft mill effluents, and the subsequentrecovery process following a pollutionabatement program. Zimmerman andLivingston (1976a) found that a pulp millon the Fenholloway River dumped from200,000 to 220,000 m3 of kraft milleffluents into Apalachee Bay over the 20year period from 1954 to 1974, at whichtime a pollution abatement program wasenacted. The effluents altered waterquality and caused increased turbidity andreduced light penetration, which, in turn,reduced species diversity of macroalgaeand reduced productivity in the baycompared with a similar region off theunpolluted Econfina River (Heck 1976;Hooks et al. 1976; Livingston 1984b). Thechanges in water quality and plantcommunities caused significant changes inthe fishes and macroinvertebrates.Numbers of individuals and species numberswere reduced in areas of severe impact.In areas of moderate but chronic impact,the annual species numbers were equivalentto control stations, but this proved to bethe result of the recruitment of a fewindividuals of rare species (Livingston1975). Livingston (1987) also noted thatalthough recovery was occurring, theseagrasses, especially Thalassia, wereslow to respond following the removal ofthe stress.

7.6 DISTURBANCE, RECOLONIZATION, ANDRESTORATION

7.6.1 Disturbance

While the large offshore seagrassmeadows in the Big Bend region of Floridahave remained relatively intact andundisturbed, the beds that are foundwithin the enclosed estuaries on the westcoast of Florida have sufferedtremendously. The greatest losses haveoccurred in Tampa Bay, where there are

95

only 5,750 ha of seagrasses remaining fromestimated

ii 970 hahistorical coverage of

a reduction of 81% (Figure 9f&n Lewi; et al. 1985a). Because of thehigh turbidity caused in part by thenow-unvegetated bottom, seagrassdistribution is presently limited to lessthan 2 m in depth in nearly all cases.The problems and destruction encounteredin Tampa Bay are not unique, but aremirrored in nearly all estuaries withheavy urbanization and industrialization(Taylor and Saloman 1968; Simon 1974;Lewis et al. 1985a; Livingston 1987).

Other estuaries on the west Floridacoast have shown similar losses (Table17). In the vicinity of Bayport,seagrasses have declined by 13% (Haddad1986). St. Joseph Bay, in an area of lowpopulation density, has not shownsignificant changes in seagrass density in15 years (Savastano et al. 1984), andApalachicola Bay has shown minimaldegradation (Livingston 1987). Thecoverage of submerged vegetation inChoctawhatchee Bay has declined by 30%since 1949 (Haddad 1986), but the causesare unknown (Burch 1983; Livingston 1987).Within the Pensacola Bay system,occasional beds of Thalassia and Haloduleare found in Santa Rosa Sound, but therewas a complete loss of seagrass inEscambia Bay, East Bay, and Pensacola Baybetween 1949 and 1979 (Olinger et al.1975; Livingston 1987). Big Lagoon, westof Pensacola, has increased coverage by55%, one of the few areas in the state todo so (Haddad 1986). In Charlotte Harbor,on the southwest coast, seagrass beds havedeclined nearly 30% to 9,300 ha remaining(Harris et al. 1983; Haddad and Hoffman1986).

7.6.2 Recolonization

The natural recolonization of seagrassesis a highly variable process, the rate ofwhich can be affected by localenvironmental parameters, as well as thespecies of the seagrass. Halodule is thenormal pioneer species in the region andcan colonize an area rapidly ifsedimentary conditions are favorable andif there is a source of seed or otherpropagule material. With its surficialrhizome system and smaller investment inbelowground biomass than the climax

species, it can rapidly cover a damagedarea.

Compared to the other seagrasses,Thalassia is much slower to recolonize adisturbed area. At least 10 months arerequired for Thalassia to begin new shortshoot development (Fuss and Kelly 1969),and the initiation of new growth seems tobe sensitive to environmental conditions.After 13 months, Kelly et al. (1971) foundthat 40% of transplanted plants in acontrol area had initiated new rhizomegrowth, while only 15% to 18% of theplants transplanted to disturbed sedimentshad initiated new growth.

It has been well documented that smalldisturbances in seagrass beds requiresurprisingly long recovery times. Themost common form of disturbance toseagrass beds in the shallow banks andbays of south Florida results from cuts byboat propellers. Although it would seemthat these relatively small-scaledisturbances would heal rapidly, ittypically takes two to five years torecolonize a Thalassia bed (Zieman 1976).The scarred areas rapidly fill in withsediment from the surrounding beds, butthe sediment is slightly coarser and has alower pH and Eh, and probably otherphysico-chemical differences that theplants can detect (the rhizome apex willfrequently grow up to one of these areasand then literally turn back into theparent bed and away from the filled-incut; Zieman 1976).

Seagrass ecosystems show differentialrecovery rates from disturbances based ona variety of factors including speciesinvolved, the type and magnitude of thedisturbance, and especially whether or notthe sediments were disturbed. Along thewest Florida coast, if the disturbance isgreat enough, a number of rhizophyticalgae act as precursors to the seagrasses.One of the primary determinants of theduration of recovery time is the extent ofdamage to the sediments. If the sedimentsand seagrass rhizomes are not severelydisturbed, the probability of recovery isgreatly increased. Table 18, (1984b),attempts to synthesize and categorize thelevels of damage to seagrass ecosystems,system effects, and the likely outcome ofthe disturbances. Although originally

96

Table 17. List of data concerning historic anthropogenous impacts on seagrass meadows in Florida (from Livingston 1987).

Study area Location Status of seagrass meadows Information source

Indian River

Biscayne Bay

Florida Keys

co4 Florida Bay

Tampa Bay

system

CharlotteHarbor

Southeast FloridaAtlantic Ocean

Southeast FloridaAtlantic Ocean

South Florida Few data found. Little effect of KeyAtlantic Ocean West desalination plant.

South Florida Postulated altered species relationshipsdue to increased salinity caused byredirection of freshwater runoff.

Southwest FloridaGulf of Mexico

Southwest FloridaGulf of Mexico

Historic declines in number and coverageof seagrass meadows. Declines in VeroBeach area, Fort Pierce Inlet (25%), andSebastian Inlet (38%) from 1951 through1984.

Undetermined deterioration in northernBiscayne Bay. Some damage to Thalassia-Halodule beds near power plant (heatedeffluents) in south Biscayne Bay. CardSound unaffected by power plantdischarge.

Almost 40% reduction in Boca CiegaBay due to dredging, filling, andassociated activity from 1950 through1968. Multiple sources (urbanization,storm water runoff, sewage discharge,industrialization, toxic substances).Reduction of seagrass meadows in TampaBay, Old Tampa Bay, and HillsboroughBay from 15,161 to 3,091 acres (1876-1980).

Decline of 29% of seagrass bedsfrom 1943 through 1984.

Goodwin and Goodwin 1976; FloridaDepartment of Natural Resources,unpubl. data

McNulty 1961; Rosessler andZieman 1969; Thorhaug et al.1973; Zieman 1970, 1982

Chesher 1971

Zieman 1982

Simon 1974; Taylor 1971;Taylor and Saloman 1968;Lewis and Phillips 1980

Florida Department of NaturalResources, unpubl. data

(Continued)

Table 17. (Concluded).

Study area Location Status of seagrass meadows Information source

Pensacola Bay Northwest FloridaSystem Gulf of Mexico

Choctawhatchee Northwest Florida Historical deterioration of seagrassBay Gulf of Mexico beds from 1949-1983. Causes unknown.

St. Andrews Bay Northwest FloridaGulf of Mexico

No data found. Presumed impact due tourbanization, industrialization.

Extensive coverage unchanged from 1972through 1983. Relatively unpopulatedarea.

St. Joseph Bay Northwest FloridaGulf of Mexico

Apalachicola North FloridaBay System Gulf of Mexico

Apalachee Bay North FloridaGulf of Mexico

Complete loss of seagrass beds inEscambia Bay, East Bay and PensacolaBay from 1949-1979. Some fresh-brackishwater species extant in delta areas.Some Thalassia-Halodule beds still alivein Santa Rosa Sound. Losses due tourbanization, industrial waste dischargedredging and filling, culturaleutrophication.

Generally healthy assemblages of sea-grasses. Local impact due to dredgedopening in associated barrier island.Introduced species spreading in deltaareas with as yet undetermined impact.Area under increased pressure fromurbanization.

Impacts due to disposal of pulp millwastes (Fenholloway Estuary) from 1954to the present. Slow recovery noted inouter portions of impact area(associated with pollution abatementprogram). Area now threatened byproposed inshore navigation channel andpossible offshore oil drillingoperations.

Livingston et al. 1972; Olinger etal. 1975; Livingston 1979

Burch 1983

McNulty et al. 1972; Savastanoet al. 1984

Livingston 198Oc, 1983

Heck 1976; Hooks et al. 1976;Livingston 1975, 1982a, 1984a;Zimmerman and Livingston 1976a,b

______I.- ..-

Table 18. Seagrass damage and restoration assessment (from Zieman et al. 1984b).

AssociatedDamage Plant community System Recovery Restorationlevel effects effects fate time indicated

1 No visibledamage

2 Leaf damageand removal

3 Severe damageto rhizomes

4 Severe systemdamage

Possible fauna1damage

Fauna1 damage maybe extensive

Fauna1 damage islikely extensive

System completelyaltered

Natural Weeks-year Norecovery

Natural 6 months- Norecovery yearlikely

Natural 5 years- Yesrecovery decadesslow orunlikely

Return to ? Nosame statenot possible

developed for the recommendation ofstrategy following an oil spill, theresults and recommendations are notspecific to any particular type of stressand are of general utility. Following adisturbance to the seagrass system, theprimary management strategy and objectivesshould be directed towards minimizing theimpact. While all efforts should bedirected towards keeping damage at levelone or two where recovery may proceednaturally, it is most important to keeplevel-three damage from becoming levelfour, where recovery or restoration to afunctioning seagrass system is notpossible. At this level oftransformation, sediment erosion isallowed to proceed to the point wherethere is insufficient sediment remainingfor seagrass colonization.

7.6.3 Restoration

According to the concept of ecologicalsuccession, there are two basic ways torestore a mature community: (1) establishthe pioneer species and allow successionto take its course, and (2) create theenvironmental conditions necessary for thesurvival and growth of the climax species.Van Breedveld (1975) noted that survival

of seagrass transplants was greatlyenhanced by utilizing a ball of sediment,as in the techniques for terrestrialtransplantation of garden plants. He alsonoted that transplantation should be donewhen the plants are in a semidormant state(as in winter) to give the plants time tostabilize, another logical outgrowth ofterrestrial technique. Where possible,the objective of restoration in general,not just of seagrasses, should be torestore the lost community or someintermediate successional stage. In somecases, restoration of the originalcommunity may not be feasible orcost-effective, and it may be necessary torestore to an earlier successional stageand allow natural successional progressionto take place.

Transplantation of seagrasses has beenattempted since the time of the wastingdisease, but there has been a dramaticincrease in its use during the past decade(See Phillips 1980; Fonseca et al. 1981,1987; Zieman et al. 1984b for recentreviews). Darovec et al. (1975) discuss avariety of techniques for restoringcoastal regions, including seagrasses, inFlorida. This publication is usefulbecause it consolidates a diverse

99

literature, but the seagrass techniquesare rudimentary and somewhat dated, andthe other reviews mentioned should beconsulted. Until recently, mosttransplant studies reported primarily ontransplant technique and survival success,and did not address environmentalvariables such as sediment type, nutrientconditions, light, turbidity, currentvelocity, and wave climate, all of whichaffect the success or failure of theexperiment (Fonseca et al. 1981, 1987).

The myriad techniques that have beentried for transplanting seagrass haveyielded highly variable results. Thosetechniques that have shown the mostconsistent success are plugs, seeds, andshoots--both anchored and unanchored(Phillips 1980). Because of the varietyof methods and the different levels ofdescription of these methods in theliterature, direct comparison amongseemingly similar methods varies fromdifficult, at best, to impossible. Table19 summarizes the relative successesrecorded in the seagrass transplantliterature.

From this diverse literature, a fewgeneralizations stand out. The mostobvious is that the plug technique is theonly one that has worked with all speciesupon which it has been tested. This isnot ecologically surprising, as the plugminimizes trauma to the roots and rhizomesby taking part of its environment along tothe new site. The plug technique provides

the highest degree of short-term sedimentstabilization of any of the methods. Onthe negative side, the plug technique islogistically more difficult due to theneed to collect the plug intact, movelarge amounts of sediment, and createsites of disturbance at the donorlocation.

Methods using bare shoots have shownmixed results, being very successful withpioneer species such as Halodule wrightiiand Zostera marina, but not reallysuccessful with Thalassia, which is aclimax species.anchoring' to

Shoot methods requireapproach the sediment

stability of the plug technique (Fonsecaet al. 1984). The logistics are somewhatsimpler than the plug method since thereis no mass of sediment to be transported.

Transplantations utilizing seeds andseedlings have been attempted for severalspecies, but have been successful onlywith Thalassia. If an abundant source ofseeds can be readily located, thistechnique can be very attractive, becauseof simple transportation and plantinglogistics. Recently, Lewis and Phillips(1981) have reported on sites of high seedavailability in the Florida Keys in latesummer. On the negative side, seeds areonly seasonally available and newly-planted seeds or seedlings do not offerany sediment stabilization capacity.However, interplanting of Thalassiaseedlings in beds of recently established

Table 19. Success of seagrass restoration techniques (from Zieman et al. 1984b).

SpeciesShoot Shoot

Plug (anchored) (unanchored) Seed

Zostera marina- - ~

Halodule wrightii

Syringodium filiforme

Thalassia testudinum

+/+ +/+ +/+ +/-

+/+ +/+ +/- __

+/+ +/+ +/- ?

+/+ +/- +/- +/+

Key: attempted/success, -- = not attempted, + = yes, - = no, ? = not sure

100

Halodule termed a "compressed successional"approach, was tested by Durako and Moffler(1984), and may prove to be a useful mixed-planting technique.

In 1982, Zieman wrote that "transplants oftropical seagrasses may ultimately be auseful restorative technique to reclaimdamaged areas, but at this time the resultsare not consistent or dependable, and thecosts seem prohibitive for any effort otherthan experimental revegetationespecial?; when the relative survival of theplants is considered." In the interveningtime, a number of additional projects havebeen completed, but the situation has notchanged significantly. Fonseca et al.(1987) stated that "for the most part,seagrass transplanting as a management toolis not working. Isolated cases of successor partial success can be found, but theseare overshadowed by many costly failures.This lack of success is largely due to thegeneral disregard for and the lack ofscientific information on environmentalrequirements of the transplant species.”Further, they feel that "the pressure tomake management decisions has growndisproportionatelytothe increase regardingseagrass habitat management. With muchemphasis having been put on methodology oftransplanting and much less on collection ofenvironmental data, we have been at a lossto explain successes and failures in aquantitative fashion."

In the State of Florida, seagrasstransplantation and restoration is oftentreated as if it were a proven-and-fixedtechnology, capable of producing a productupon specification, when, in fact, it isreally a series of loosely coupledexperiments. The concept of seagrasstransplanting for "mitigation" ofenvironmental damages is becoming anaccepted practice in Florida under theassumption that if an environmentaldisturbance or destruction is "necessary"or "in the public interest," then thisperturbation can be "mitigated" by aparallel restoration. As a step towardaccepting seagrass transplanting as a viablemitigation method, numerous Federal, State,and local agencies have funded projectsaimed at seagrass restoration. However,only recently have any studies been fundedto conduct a scientific investigation on theenvironmental variables causing the success

or failure of a particular project. Severalrecent projects have elegantly tested theviability of different methodologies in aproper scientific manner, but none of thesecan tell whv a particular method succeededor failed.

One of the major problems in offsiterestoration as it is currently practiced,is the selection of a suitable andpotentially viable site for restoration, ifit is not to be the recently disturbed site.Many times the sites chosen areinappropriate and there are sound ecologicalreasons why seagrasses are not growing therenow, even if there was seagrass coverage atsome point in past history (Lewis et al.1985a; Fonseca et al. 1987). If it can beestablished that an area meets theenvironmental conditions to supportseagrasses, but has probably not recovereddue to lack of natural propagules, thenrestoration may be indicated.Unfortunately, probably the major probleminhibiting seagrass success today is thedeteriorating water quality associated withindustrialization and development. If poorwater quality increases turbidity anddecreases incident light at the sedimentlevel past a certain point, then all thetransplanting in the world will not work.In any restored area, the plants must havesufficient light to yield a significantlyhigh positive net photosyntheses to surviveand grow. If turbidity is too high, oreutrophication is sufficient to cause arapid growth of epiphytic algae orphytoplankton, then the effort and moneywill be wasted.

7.7 FINAL THOUGHTS

The gathering and assimilation of data forthis community profile has been highlyenlightening. Dozens of studies have shownthe importance of submerged vegetation tomajor commercial and forage organisms(Linda11 and Saloman 1977; Thayer et al.1978a; Peters et al. 1979; Thayer and Ustach1981). In the gulf States the recreationalsaltwater fish catch exceeded $168 millionin 1973, representing about 30% of the totalU.S. recreational fishery (Linda11 andSaloman 1977). Of the organisms caught, 59%were dependent on wetlands at some state oftheir life cycles. In the Gulf of Mexico,this estimate was even higher with over 70%

101

of gulf recreational fisheries of the regionbeing estuarine dependent. The ecologicaldependence of important commercial fisherieson the estuarine wetlands is even greater.The Gulf of Mexico is the leading region ofthe United States in terms of both landings(36% of the total U.S. catch) and value (27%of total U.S. fishery value), and 90% of thetotal Gulf of Mexico and south Atlanticfishery catch is estuarine dependent(Linda11 and Saloman 1977).

The west Florida coast contains vastseagrass resources, in the form of offshorebeds of the Big Bend region, that have beenlargely untouched by human activities.However, the seagrass resources within thewest Florida estuaries must rank alongside

the seagrasses of Chesapeake Bay as some ofthe most devastated and degraded in theentire country (Lewis et al. 1985a;Livingston 1987). The importance of theselosses to both the ecology and the economyof Florida are far out of proportion to thetotal hectares lost versus those remaining,due to the critical nature of the estuarineseagrass beds as nurseries. While measuresmust be taken to ensure the continuedproductivity of the offshore beds, it ismost critical that the water qualitydegradation that has caused the extensivelosses in the estuarine grass beds bearrested and reversed. Once the beds aretotally destroyed, they are likely to remainlost forever, along with the myriadorganisms that they feed and shelter.

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Arber, A. 1920. Water plants: study ofaquatic angiosperms. S-H Serv.Inc., Riverside, N.J.

Atkinson, M.J., and S.V. Smith.C:N:P ratios of marine benthicLimnol. Oceanogr. 28:568-574.

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Austin, H.W. 1970. Floridaground. Mar. Pollut.1(11):171-172.

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Bach, S. 0. 1979. Standing crop, growthand production of calcareous Siphonales(Chlorophyta) in a south Florida lagoon.Bull. Mar. Sci. 29(2): 191-201.

Bader, R.G. and M.A. Roessler. 1971. Anecological study of south Biscayne Bayand Card Sound, Florida. Prog. Rep.USAEC contract AT(40-l)-3801-3. Sch.Mar. and Atmos. Sci., University ofMiami.

Baird, R.C., K. Rolfes, B. Causey, W.fable, A. Feinstein, and D. Milliken.1971. Fish. in Anclote environmentalproject annualreport 1971. Prep. forFla. Power Corp. by Mar. Sci. Institute,University of South Florida. 251 pp.

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126

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128

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129

NWRC

This page has been left blank intentionally

APPENDIX

FISH SPECIES SURVEYS IN SOUTH AND WESTERN FLORIDA

Use these keys to interpret the table that follows.

Key to survey numbers

Survey No. Location Reference

1 North Biscayne Bay2 South Biscayne Bay3 Card Sound4 Matecutie Key5 Porpoise Lake6 Whitewater Bay

:Fakahatchee BayMarco Island

9 Rookery Bay10 Charlotte Harbor11 Offshore Tampa12a Tampa Bay Mouth to Offshore

Reefs (Stns. 1 - 3)12b Tampa Bay Grassbed Stations

(Stns. 4 - 6)13 Crystal Bay Area14 Cedar Key15 Alligator Harbor

16 Apalachicola Bay

Key to abundance

Roessler 1965Bader and Roessler 1971Brook 1975Springer and McErlean 1962Hudson et al. 1970Tabb and Manning 1961Carter et al. 1973Weinstein et al. 1971Yokel 1975aWang and Raney 1971Pbe and Martin 1965Springer and Woodburn 1960

Springer and Woodburn 1960

Mountain 1972Reid 1954Joseph and Yerger 1956;Yerger 1961Livingston 1984

Note:

= rare= present= abundant= common

Species names are according to Robbins et al. 1980, except where anasterisk (*) indicates that they are given as originally published.

131

Appendix (Continued).

Abundance by survey numberSpecies 1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Orectolobidae/carpet sharks

Ginglymostoma cirratum r r P P Pnurse shark

Carcharhinidae/requiem sharks

Negaprion brevirostrislemon shark

Rhizoprionodon terraenovaeAtlantic sharpnose shark

Carcharhinus acronatusblacknose shark

Carcharhinus isodonfinetoothed shark

Carcharhinus leucasbull shark

Carcharhinus limbatusblacktip shark

Carcharhinus plumbeussandbar shark

Sphyrnidae/hammerhead sharks

t i b u r oSphyrnabonnethead

diplana*Sphyrna

Sphyrna mokarrangreat hammerhead

Pristidae/sawfishes

Pristis pectinatasmalltooth sawfish

Rhinobatidae/guitarfishes

Rhinobatus lentiginosusAtlantic guitarfish

P

r

P

P

(Continued)

132

P

P P

P

P P P

PP P

P

P PP P

P

P

P

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Torpedinidae/electric rays

Narcine brasiliensislesser electric ray

Rajidae/skates

Raja texanaroundel skate

Raja eglanteriaclearnose skate

r

r

Dasyatidae/stingrays

Urolophus jamaicensis r ryellow stingray

m i c r u r aGymnurasmooth butterfly ray

Dasyatis americana"southern stingray

Dasyatis sabinaAtlantic stingray

Dasyatis sayiblunt nosed stingray

Myliobatidae/eagle rays

Aetobates narinarispotted eagle ray

Rhinoptera bonasuscownose ray

Mobulidae/mantas

Manta birostisAtlantic manta

Lepisosteidae/gars

Lepisosteus osseuslongnosed gar

Lepisosteus platyrhinchusFlorida gar

r r

P

r r P P P P P P

P

r r P P P

P P

P

a P P

P P

P P P

(Continued)

133

Appendix(Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Elopidae/tarpons

Elops saurusladyfish

Megalops atlanticustarpon

Albulidae/bonefishes

Albula vulpesbonefish

Anguillidae/freshwater eels

Anguilla rostrataAmerican eel

Muraenidae/morays

Gymnothorax nigromarginatus rblackedge moray

Gymnothorax saxicolaocellated moray

Ophichthidae/snake eels

Myrophis punctatusspeckled worm eel

Ophichthusshrimp eel

gomesi

Echiophis intertinctusspotted spoon-nose eel

Echiophis mordaxsnapper eel

Bascanichthys bascaniumsooty eel

Bascanichthys scuticaniswhip eel

Clupeidae/herrings

Harengula jaguanascaled sardine

P

P

P

r r r r

r r

r r r r c

P P

P

P

P

P a

P P

rr P

r

P P

P P

P P

P

aa P P P P

(Continued)

134

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Clupeidae/herrings (continued)

Harengula humeralis rredear sardine

Jenkinsia sp.

Brevoortia smithiyellowfin menhaden

Brevoortia patronusgulf menhaden

Etrumeus sadina"

Dorosoma petenensethreadfin shad

Opisthonema oglinumAtlantic thread herring

Sardinella auriaSpanish sardine

Engraulidae/anchovies

Anchoa cubanaCubananchovy

Anchoa lamprotaeniabigeye anchovy

Anchoa mitchillibay anchovy

Anchoviella perfasciataflat anchovy

Anchoa hepsetusstriped anchovy

Synodontidae/lizardfishes

foetensSynodusinshore lizardfish

Synodus intermediussand diver

r

r r

r

r

r

pap PP

P

P P

a P p P

P a P

r P P

a P

r r p c r r c a a P P P P

r

r r r c PP P P P

r r r r p c r r r r p p p P P P

P

(Continued)

135

PAppendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Ictaluridae/bullhead catfishes

Ictalurus catuswhite catfish

Ictalurus nebulosusbrown bullhead

idae/sea catfishesAri

P

P

m a r i n u sBagregafftopsail catfish

Arius felishardheadcatfish

Batrachoididae/toadfishes

Opsanus betagulf toadfish

Opsanus pardusleopard toadfish

Porichthys plectrodonAtlantic midshipman

Gobiesocidae/clingfishes

Acyrtops beryllinusemerald clingfish

P r r r

c a r r p c c c r

r

Gobiesox strumosusskilletfish

Antennariidae/frogfishes

Histrio histriosargassumfish

Antennarius ocellatusocellated frogfish

Ogcocephalidae/batfishes

Ogcocephalus cubifrons"

Ogcocephalus nasutus rshortnose batfish

r

r

r P r

P P

r P P P P P

P P P P P P

P P

r P P

P P P P

r r

P

r

P P

(Continued)

136

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Ogcocephalidae/batfishes (Continued)

Ogcocephalus radiatuspolka-dot batfish

P

Ogcocephalus sp. P P

Halieutichthys aculeatuspancake batfish

Gadidae/codfishes

Urophycis floridanasouthern hake

Ophidiidae/cusk-eels

Lepophidium jeannaemottled tusk-eel

Ophidion grayiblotched tusk-eel

Ophidion welshicrested tusk-eel

Ophidion holbrookibank tusk-eel

Ophidion beanilongnose tusk-eel

Ophidion marginatumstriped tusk-eel

Bythitidae/viviparous brotulas

c a y o r u mOgilbiakey brotula

Gunterichthys longipenisgold brotula

Carapidae/pearlfishes

b e r m u d e n s i sCarapuspearlfish

r

r

r r

P

P

r

P

r P

P

P

P P

(Continued)

137

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Exocoetidae/flyhalfbeaks

Hemiramphusballyhoo

i ng fishes and

brasiliensis

Chriodorus atherinoideshardhead halfbeak

Hyporhamphus unfasciatushalfbeak

Belonidae/needlefishes

Strongylura notataredfin needlefish

Strongylura timucutimucu

Strongylura marinaAtlantic neemh

crocodilusTylosurushoundfish

Tylosorus raphidoma"

Cyprinodontidae/killifishes

Flordichthys carpiogoldspotted killifish

Adinia xenicadiamondkillifish

Lucania parvarainwater killifish

Fundulus heteroclitusmummichog

Fundulusgulf kill

grandisIfish

Fundulus similislongnose killifish

Fundulus confluentusmarsh kil'lifish

r

P

p r

r r p r

r r

r

c a r

r

a r r p r

r

r

r r

PPP P

PPP P

a P

P P

P

P P

r P

P P P P P

PP P

r P P

P

(Continued)

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Cyprinodontidae/killifishes (continued)

P r P PCyprinodon variegatussheepshead minnow

Rivulus marmoratusrivulus

r

Poeciliidae/livebearers

P r P PPoecilia latipinnasailfin molly

Gambusia affinismosquitoflsh

r P

rHeterandria formosaleast killifish

Atherinidae/silversides

C r P

a a

Hypoatherina harringtonensisreef silverside

Atherinomorus stipeshardhead silverside

r c a a P P PMenidia beryllinatidewater silverside

Membras martinicarough silverside

Membras vagrans"

Membras sp.

Holocentridae/squirrelfishes

r r

a P

Holocentrus ascensionissquirrelfish

Syngnathidae/pipefishes andseahorses

a

Cosmocampus albirostris r rwhltenose pipefish

r

Cosmocampus brachycephaluscrested pipefish

r

(Continued)

139

Appendix(Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Syngnathidae/pipefishes andseahorses (continued)

Hippocampus hudsonius*

Hippocampus zosteraedwarf seahorse

Hippocampus erectuslined seahorse

Hippocampus reidilongsnout seahorse

Hippocampus regulus*

Hippocampus sp.

Syngnathus sp.

Syngnathus dunckeripugnose pipefish

Syngnathus floridaedusky pipefish

Syngnathus louisianaechain pipefish

Syngnathus elucensshortfin pipefish

Syngnathus springeribull pipefish

Syngnathus scovelligulf pipefish

Micrognathus crinigerusfringed pipefish

Centropomidae/snooks

Centropomus undecimalissnook

Serranidae/sea basses

Centropristis striatablack sea bass

r

r c r r p r r r r

r r r r r r

r

r

c r r r p r r r

r r r r r r r r

r r c r p c a c c c

a r P r

P P P P

P

P

P

P

P P P

P P P

P P P

P P

P P

r r P P P P

(Continued)

140

Appendix(Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Serranidae/sea basses

Centropristis ocyurusbank sea bass

Mycteroperca bonaci rblack grouper

Mycteroperca microlepis r rgag

Mycteroptera falcata"

Serraniculus pumiliopygmy sea bass

Serranus subliqariusbelted sandfish

Diplectrum bivittatumdwarf sand perch

Diplectrum formosumsand perch

Epinephalus moriored grouper

Epinephalus itajara Pjewfish

Epinephalus adscensionisrock hind

Grammistidae/soapfishes

Rypticus saponaceusgreater soapfish

Apogonidae/cardinalfishes

Phaeoptyx conklinifreckled cardinalfish

Apogon aurolineatusbridle cardinalfish

Astrapogon alutus r rbronze cardinalfish

P

p rrr a

r P P

r P a

P

P

P P.

P

r

r r r r r p P P P P

P a P

P

r

P

r

P

P R P

(Continued)

141

Appendix (Continued).

Abundance by survey numberSpecies 1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Apogonidae/cardinalfishes (continued)

Astrapogon stellatus rconchfish

Pomatomidae/bluefishes

Pomatomus saltatrixbluefish

Rachycentridae/cobias

Rachycentron canadumcobia

Echeneidae/remoras

Echeneis naucratessharksucker

Carangidae/jacks and pompanos

Caranx hipposcrevalle jack

Caranx latushorse-eyejack

Caranx ruber-jack

Caranx bartholomaeiyellow jack

Caranx crysosblue runner

Hemicaranx amblyrhynchusbluntnose jack

Trachinotus falcatuspermit

Trachinotus carolinusFlorida pompano

Trachinotus sp.

Trachurus lathamirough scad

r

r

r

r P

P

(Continued)

142

r

P P P P P

P P P

P P P P P

P P P P

P

r P

P

a

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Carangidae/jacks andpompanos (continued)

Seriola zonatabanded rudderfish

Chloroscombrus chrysurusAtlantic bumper

Oligoplites saurusleatherjacket

Selene vomerlookdown

Vomer setapinnisAtlantic moonfish

Lutjanidae/snappers

Lutjanus analismutton snapper

Lutjanus apodusschoolmaster

Lutjanus griseusgray snapper

Lutjanus jocudog snapper

Lutjanus synagrislane snapper

Lutjanus campechanusred snapper

Rhomboplites aurorubensvermilion snapper

c h r y s u r u sOcyurusyellowtail snapper

Lobotidae/tripletails

Lobotes surinamensistripletails

P r

r

r r

r a P

r r c p r r r r

r

r

r r

r

a a

P P P P P

r P P P P P

r r P P P P

P P

P P P P P P

p c r a c r p P

P

P

P P

P

P

(Continued)

143

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Gerreidae/mojarras

Eucinostomus argenteusspotfin mojarra

Eucinostomus gulasilver jenny

Eucinostomus lefroyimottled mojarra

Gerres cinereusyellowfTiii$Z%a

Diapterus plumieristriped mojarra

Haemulidae/grunts

Haemulon flavolineatumFrench grunt

Haemulon parraisailors choice

Haemulon sciurusbluestriped grunt

Haemulon aurolineatumtomtate

Haemulon plumieriwhite grunt

Haemulon carbonariumCaesar grunt

Anisotremus virginicusporkfish

Orthopristis chrysopterapigfish

Sparidae/porgies

Archosargus probatocephalussheepshead

Archosargus rhomboidalissea bream

r c c r p r r r r c p a P P P P

r r a a p a a a a a P P P P P P

r

r r

r r r c

r c r p r

r r

a r a

r

r

r

a r

P

P P

a r P

P a P P P

r

r p c a a a r pa P P P P

r p r r

r

(Continued)

144

r p a p P P

P P

Appendix (Continued).

Abundance by survey numberSpecies 1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Sparidae/porgies (continued)

r h o m b o i d e s,'QcJ&I;: c c r c p a a a a a p a a P a P P

Calamus arctifronsgrass porgy

Calamus calamussaucereye porgy

Diplodus holbrookispottail pinfish

Sciaenidae/drums

Menticirrhus saxatilisnorthern kingfish

Menticirrhus littoralisgulf kingfish

Sciaenops ocellatusred drum

Bairdiella chrysourasilver perch

Cynoscion nebulosusspotted seatrout

acuminatusEquetushigh-hat

Fquetus lanceolatusJackknife fish

Bairdiella batabanablue croaker

Odontoscion dentexreef croaker

Leiostomus xanthurusspot

Cynoscion arenariussand seatrout

Micropogonias undulatusAtlantic croaker

r

r r

r

r

r

r

P r r P P P P P

C aaCC PP a pp P

p r c r r r p r p P P P P

P a

Pr rp P P

C P

a

P P P P P

P P

P

P

P

ca pa a P P P P

r r rp PP p P P

r p P P P

(Continued)

145

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Sciaenidae/drums (continued)

Pogonias cromisblack drum

a

Stellifer lanceolatusstar drum

Larimus fasciatusbanded drum

Menticirrhus americanus r r c P Psouthern kingfish

Mullidae/goatfishes

Pseudupenueus maculatus rspotted goatfish

Ephippidae/spadefishes

Chaetodipterus faberAtlantic spadefish

Chaetodontidae/butterflyfishes

Chaetodon ocellatusspotfin butterflyfish

Pomacanthidae/angelfishes

Holacanthus bermudensisblue angelfish

Pomacanthus arcuatusgray angelfish

Pomacentridae/damselfishes

Pomacentrus leucostictusbeaugregory

Pomacentrus variabliscocoa damselfish

Abudefduf saxatilissergeant major

Chromis enchrysurusyellowtail reeffish

P

P P

P P

P P P P

r P r r r PP P P P P P

P

P

r

r

(Continued)

146

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Labridae/wrasses

Doratonatus megalepis rdwarf wrasse

Halichoeres bivittatusslippery dlck

Halichoeres caudalispainted wrasse

Halichoeres radiatuspuddingwife

Hemipteronotus martinicensisrosy razorfish

Hemipteronotus novaculapearly razorfish

Lachnolaimus maximushogfish

Scaridae/parrotfishes

Nicholsina ustaemerald parrotfish

Scarus coelestinusmidnight parrotfish

Scarus croicensisstriped parrotfish

Scarus guacamaiarainbow parrotfish

Sparisoma chrysopterumredtail parrotfish

Sparisoma radiansbucktooth parrotfish

Sparisoma rubripinneredfin parrotfish

Sparisoma viridestoplight parrotfish

Cryptotomus auropunctatus"

r

C

r

r p

r

r r

r

r

r

r

r

a r C

r

r

a r

r

P

P

P

P P P

(Continued)

147

Appendix (Continued).

Species

Mugilidae/mullets

Abundance by survey number1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

c e p h a l u sMugilstriped mullet

Mugil curemawhite mullet

r P a a a P P

r r P C P P P

t r i c h o d o nMugil r P Pfantail mullet

Mugil sp.

Sphyraenidae/barracudas

Sphyraena barracudagreat barracuda

Sphyraena borealisnorthern sennet

Sphyraena sp.

Polynemidae/threadfins

Polydactylus octonemeusAtlantic threadfin

Opistognathidae/jawfishes

Opistognathus maxillosus rmottled jawfish

Opistognathus macrognathusbanded jawfish

r r r p r

Dactyloscopidae/sand stargazers

Dactyloscopus tridigitatus r rsand stargazer

Uranoscopidae/stargazers

Astroscopus y-graecumsouthern stargazer

Clinidae/clinids

Bramerella sp.*

(Continued)

148

a P

P

r r

P

P

P P

PP P P P

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Clinidae/clinids

Malacoctenusrosy blenny

Malacoctenus

(Continued)

macropus r

culebrae*

Emblemaria atlanticabanner blenny

Paraclinus fasciatusbanded blenny

Paraclinus nigripinnisblackfin blenny

Paraclinus marmoratusmarbled blenny

Chaenopsis ocellatabluethroat pikeblenny

Blenniidae/combtooth blennies

Chasmodes saburraeFlorida blenny

Parablennius marmoreusseaweed blenny

Lupinoblenniushighfin blenny

Blennius sp.

Hypleurochiluscrested blenny

nicholsi

geminatus

Hypsoblennius hentzifeather blenny

Hypsoblennius ionthasfreckled blenny

r r c

r

r r r r p

P

r r r r r r

P

Callionymidae/dragonets

Callionymus pauciradiatus r r r r pspotted dragonet

Callionymus calliurus"

r

P P

P

P

P P P P

P a

P

P

P

P P P P P

P

(Continued)

149

Appendix (Continued).

1 2 3 4Abundance by survey number

5 6 7 8 9 10 11 12a 12b 13 14 15 16Species

Gobiidae/gobies

Barbulifer ceuthoecusbearded goby

r

P

per r

r

Microgobiusbanner goby

Microgobiusclown goby

Microgobiusgreen goby

microlepis r

gulosus

thalassinus

MicrogobiusSeminole goby

carri_..

P P P P

a

Bathygobius curacaonotchtongue goby

C

Bathygobius soporatorfrillfin goby

r P

Coryphopterus sp.

Gobionellus hastatussharptail goby

P P

P PrGobionellus bolesomadarter goby

Gobionellus smaragdusemerald goby

r

Gobionellus shufeldtifreshwater goby

r

Gobionellus stigmaturusspottail goby

r

a r r p c c r r r

r

Gobiosoma robustumcode goby

a P P

Gobiosoma longipalatwoscale goby

Gobiosoma macrodontiger goby

r r P P

Gobiosoma longurn" r

(Continued)

150

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Gobiidae/gobies (continued)

Gobiosoma boscinaked goby

Ioglossus calliurusblue goby

Lophogobius cyprinoides rcrested goby

Coryphopterus glaucofraenum rbridled goby

Acanthuridae/surgeonfishes

Acanthurus bahianusocean surgeon

Acanthurus coeruleusblue tang

Acanthurus chirurgusdoctorfish

Trichiuridae/cutlass fishes

Trichiurus lepturusAtlantic cutlassfish

Scombridae/mackerels

Scomberomorus maculatusSpanish mackerel

Scomberomorus cavallaking mackerel

Euthyhnus alletteratuslittle tunny

Thunnus atlanticusblackfin tuna

Istiophoridae/billfishes

Istiophorus platypterussailfish

r

P

r

P

P P P

a P P

a P

P

r

P

P P

P P

P

(Continued)

151

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Stromateidae/butterfishes

Peprilus burtigulf butterfish

Peprilus paru*

Peprilus alepidotusharvestfish

Peprilus triacanthusbutterfish

Nomeus gronoviiman-of-war fish

Scorpaenidae/scorpionfishes

Scorpaena brasiliensisbarbfish

Scorpaena grandicornispiumed scorpionfish

Scorpaena plumeirispotted scorpionfish

Triglidae/searobins

Bellator militarishorned searobin

Prionotus pectoralis*

Prionotus salmonicolor

blackwing searobin

Prionotus scitulusleopard searobin

Prionotus tribulusbighead searobin

Prionotus roseusbluespotted searobin

r

r r r

r r r

r

r P

r r r r r r r P

r r r c rr P

P

P

P P

P P

P

prr P

P P P P

P P P P

(Continued)

152

Appendix(Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Bothidae/lefteye flounder

Bothus ocellatuseyed flounder

Ancylopsetta quadrocellataocellated flounder

Cyclopsetta fimbriattaspotfin flounder

Citharichthys macropsspotted whiff

Citharichthys spilopterusbay whiff

Paralichthys albiguttagulf flounder

Paralichthys lethostigmasouthern flounder

p a p i l l o s u mSyaciumdusky flounder

Etropus crossotusfringed flounder

Etropus rimosusgray flounder

Soleidae/soles

Thunnus atlanticusblackfin tuna

Istiophoridae/billfishes

Istiophorus platypterussailfish

Stromateidae/butterfishes

Peprilus burtigulf butterfish

Peprilus paru*

Peprilus alepidotusharvestfish

r r r

r

r r

r r

r r

P P

r P P P P P

P P

P

P r P P P

P

P P P

r r P P

r r r r PP P P P P

P P

P

P P

P P

(Continued)

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Stromateidae/butterfishes (continued)

Peprilus triacanthusbutterfish

P

r

r r

Nomeus gronoviiman-of-war fish

Trinectes inscriptusscrawled sole

r r r

r r r p c c

PP PP

PP PP

Trinectes maculatushogchoker

r rAchirus lineatuslined sole

Cynoglossidae/tonguefishes

r r r c c r P

P

PP PPSymphurus plagiusablackcheek tonguefish

Symphurus diomedianusspottedfin tonguefish

stidae/triggerfishes andfilefishes

Balistes capriscusgray triggerfish

Bal i

r P

c r r c r r a a P P P

c r r c r rrrr PP P P P

r P P

Monocanthus ciliatusfringed filefish

Monocanthus hispidusplanehead filefish

Alutera zchoepfiorange filefish

Ostraciidae/boxfishes

Lactophrys quadricornis r cscrawled cowfish

r r P r r P

r

P

r rLactophrys trigonustrunkfish

C P

rLactophrys triquetersmooth trunkfish

r

(Continued)

154

Appendix (Continued).

SpeciesAbundance by survey number

1 2 3 4 5 6 7 8 9 10 11 12a 12b 13 14 15 16

Tetraodontidae/puffers

Sphoeroides nephelus r r p r c r r PP P P Psouthern puffer

Sphoeroides spengleri r r r r r r Pbandtail puffer

Sphoeroides marmoratus*

Sphoeroides harperi*

P

P

r

P

Sphoeroides testudineuscheckered puffer

Lagcocephalus laevigatussmooth puffer

Diodontidae/porquepinefishes

Chilomycterus schoepfi r c r r p r r c r r p p p pstriped burrfish

Chilomycterus antennatus rbridled burrfish

Diodon holocanthus r r P rballoonfish

P P

155

so272 -101

REPORT DOCUMENTATION 11. REPORT NO.PAGE 1 Biological Report 85(7.25) 1'.

.____--. .._ _..______._______ __~__4. TotIe and Subtetls

The Ecology of the Seagrass Meadows of the West1 September 1989

Coast of Florida: A Community Profile i6.

7. Author(r)Joseph C. Zieman and Rita T. Zieman

3r.s~_ _____-

lo. ProlKt/Tatk/Work “n,t N o .

Department of Environmental Sciences 11. COntrXtK) or Grant(G) No.

University of VirginiaCharlottesville, VA 22903

12. Soonrorm6 Orsamratton Name and Addrers_ _ .___~~

13. Type of Repart 6 Penod C o v e r s ,

U.S. Department of the InteriorFish and Wildlife ServiceNational Wetlands Research Center - - - -

Washington, DC 20240

_ _ __ _ _ _ ___ .~

16. Abstract (Limit: 200 wards,

This report summarizes information on the ecology of seagrass meadows on the west coastof Florida, from south of Tampa Bay to Pensacola. This area contains more than 3,500 haof seagrass beds, dominated by three species, Thalassia testudinum (turtle grass),Syringodium filiforme (manatee grass), and HaTodule wrightii (shoal grass). Beds occurboth on the shallow,

_____zero-energy Continental Shelf and in inshore bays and estuaries.

Species ecology, distribution, biomass, and productivity of these dominant seagrassspecies are discussed.

Seagrass beds support a very diverse and abundant algal flora and fauna, and theseorganisms and seagrass detritus form the base of a productive food chain. Seagrass bedsare important nursery areas providing both cover and food, for a number of commercial andsports fishery species.

Along the west Florida coast, estuarine grass beds are noticeably more stressed andimpacted by human activities than the more pristine nearshore beds. Urban developmentand dredging and filling are the major threates to seagrass beds in this region.

_ _ _1 7 . D o c u m e n t Analysn a. Descnptors

Ecology SyringodiumAquatic beds HaloduleThalassia Halophila

b. Identihsn/Own~Endcd T e r m s

Seagrass EcosystemFlorida gulf coast Nursery utilization

c. COSATI F i e l d / G r o u p

16. AvaIlability S t a t e m e n t 1 9 . Secunty Class (Thns Report)

Unlimited distribution : 20. Sccurfty C l a s s Vh!s Page)

(See ANSI-239.16) OPTIONAL FORM 2?2 (4-7(Formcrl. N T I S - 3 5 )Dcp*rtment at commerce