epiphytic diatoms of three seagrass species in mississippi sound (ecologia)

7/24/2019 Epiphytic Diatoms of Three Seagrass Species in Mississippi Sound (Ecologia)

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BULLETIN OF MARINE SCIENCE, 29(4): 459-464, 1979

EPIPHYTIC DIATOMS OF THREE SEAGRASS SPECIES IN

MISSISSIPPI SOUND

Michael J. Sullivan

ABSTRACT

Epiphytic diatoms were collected on 20 July 1977from the leaves of three seagrass species

(Halodule beaudettei, Cymodoceafiliforme, and Thalassia les(udinum) in Mississippi Sound,

U.S.A. Examination of cleaned material under the light and scanning electron microscope

revealed a total of 45 diatom taxa epiphytic on the three seagrasses. The four most abundant

diatoms were Fragilaria hyalina, Maslogloia pusilla, Ucmophora cr. debilis, and Opephora

pacifica. Except for the rare taxa, the taxonomic composition was identical regardless of the

seagrass species examined. Based on counts of 1,000 valves, values of community diversitystatistics (H', S, and R') were virtually identical for the three epiphytic diatom samples. Use

of a selected similarity index (SIMI) revealed that any two samples shared between 82 and

88% of the maximum similarity possible. Therefore, the available taxonomic and structural

information indicated that the above three seagrasses supported a single, nearly homoge-

neous epiphytic diatom community at the time of sampling.

Seagrasses are highly productive marine angiosperms which produce annualcrops of leaves from perennial rhizomes buried in the sediment. Depending onlocal conditions, various seagrass beds may support a prolific epiphytic algal floraon the leaves. Such severe epiphytism may lead to significant decreases in sea-grass productivity (Sand-Jensen, 1977). Recent work on Zostera marina L. bedsin North Carolina waters has shown that over a one-year period algal epiphytesaccounted for 24% of the total biomass and ]8% of the total productivity on anareal basis of the seagrass-epiphyte community (Penhale, 1977). The presence ofalgal epiphytes should presumably increase the nutritive value and utilization ofseagrass species by various faunal elments. Wood (1959) found that diatoms epi-

phytic on Australian seagrasses were an important food source for phytophagousfish and other animals over a yearly cycle.

Published accounts of those algal species epiphytic on seagrasses within watersof the continental United States have been rare indeed. Humm (1964) and Bal-

lantine (1972) reported on blue-green, red, brown, and green algae epiphytic onfour seagrass species off the east and west coast of Florida, respectively. Thediatom component of seagrass epiphytic floras has received attention in only onestudy on the Pacific coast (Main and McIntire, 1974) and two on the Atlanticcoast (Reyes-Vasquez, 1970; Sullivan, 1977). Therefore, our knowledge of thediatom flora epiphytic on seagrasses in the Gulf of Mexico is nonexistent. Thepresent paper presents some preliminary information as a first step in alleviating

this unfortunate situation.

DESCRIPTION OF STUDY AREA

Within Mississippi Sound seagrass beds are primarily found associated with a sandy boltom andshallow waters along the northern shores of the four barrier islands: Cat, Ship, Horn, and Petit Bois.

The dominant seagrass species are shoal grass, Halodule beaudettei (Den Hartog) Den Hartog; turtlegrass, Thalassia lesludinum Konig; and to a lesser extent manatee grass, Cymodoceafiliforme (Klitz,)

Correll (=Syringodium filiforme Klitz.). The study area was located approximately 0.3 km north ofHorn Island. Water depth over the seagrass beds studied ranges from 0.8 to 1.4 m below MLW.

Summer water salinities in the study area generally range from 20 to 35 and average about 3 0 " 1 0 0 . All

three seagrass species were present in the study area forming pure or occasional mixed beds of

variable size.

459


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460 BULLETIN OF MARINE SCIENCE, VOL. 29, NO.4, ]979

METHODS

A single preliminary collection of epiphytic diatoms from the three seagrass species was made on

20 July 1977. The salinity of Mississippi Sound on this particular date was 34% 0 following a droughtof approximately 2 months duration. Heavily epiphytized leaves were removed by hand from threeindividual beds, each bed being composed of a single seagrass species, Virtually all leaves present ineach bed were so completely covered with a dense growth of Ectocarplls and diatoms that the greencolor of the seagrass was all but undetectable. Epiphytic diatoms were removed by scraping individualleaves with a spatula. The leaves were examined visually following epiphyte removal and none ap-peared to be senescent. Three epiphytic diatom samples were thus obtained, each one representative

of a single seagrass species. Each sample was then boiled in nitric acid and potassium dichromate tooxidize the organic matter and prepare the diatom valves for observation under both the light (LM)and scanning electron microscope (SEM). One-half of the cleaned material in each sample was mount-ed in Hyrax (LM) while the remaining half was air-dried on aluminum stubs and then coated withgold in a sputtering device (Technics, Inc.) for observation in a Hitachi HHS-2R SEM operated at anaccelerating voltage of 20 KV. Although all counts for the data analysis were made with the LM,

identification of some of the diatom taxa would have been difficult, if not impossible, in the absenceof SEM observations.

Data Analysis

At least 1,000 diatom valves were counted and identified to species or varietal rank in each of the

three samples. This number represented a small percentage of the total number of valves present ina given sample. After each sample had been analyzed taxonomically, community diversity statisticswere calculated. The first of these was the Information index (Shannon and Weaver, 1949):

where H' (species diversity) is expressed as bits/individual, nj is the number of individuals of the

i-th taxon, N is the total number of individuals, and S is the total number of taxa in the sample. Thesecond index of community diversity calculated was redundancy (Main and McIntire, 1974):

R' = H'm.x - H'

H'max - H'min '

where

H'max = log,S,and

(N-S+l)

H'mln =10g,N - N 10g,(N - S + I).

R' has no units and is a useful measure of the relative degree of dominance in the sample. Values ofR' range from 0, when all taxa are equally abundant, to I, when all taxa except one are representedby a single individual. To compare the structure of selected pairs of diatom communities the following

similarity index proposed by Stander (1970) was employed:

s

2 : PUPlnSIMI =

1=1

~1~1

Pu ' ~ItPIn'where Pi ) and Pin are the proportions of the i-th taxon in the j-th and n-th samples, respectively, and

S is the total number of taxa. If the two samples being wmpared share no taxa in common, SIMI has

a minimum value of 0; whereas, if the taxa present and their relative abundance are identical in both

samples, SIMI has a maximum value of I.

RESULTS

A total of 37 diatom taxa were identified from the three samples counted under

the LM. The identity and relative abundance of each diatom taxon is listed for

each seagrass species in Table I. Additional LMscans following the cessation of


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SULLIV AN: EPIPHYTIC SEAGRASS DIATOMS 4 6 1

Table I. Relative abundance of diatom taxa epiphytic on seagrasses in Mississippi Sound expressedas number of individuals in a sample (HB =Halodule beaudettei. CF =Cymodocea filiforme,rr= Thalassia testudinum. and ~ nl =three samples pooled as one)

Diatom Taxon HB CF IT In,

Achnanthes hauckiana Grun. t IAmphora coffei/ormis (Ag.) Kiitz. 6 6A. cymbelloides Grun. 2 2A. cymbiformis CI. 2 3 7 1 2A. exigua Greg. 1 I 2A. ol'alis var. pediculus (Kiitz.) V.H. 16 2 5 3 6 7 7A. proteus Greg. 3 I 4A. tenuissima Hust. 3 7 4 6 7 6 15 9Berkeleya rlllilans (Trent.) Grun. 6 I 7Cocconeis deperdita Giffen 3 7 1 0

C. placentu/a var. euglypta (Ehr.) CI. 4 7 9 2 5 8C. sculellum Ehr. 2 6 1 5 4 1C. woodii Reyes-Vasquez 5 1 0 I 1 6Cye/olella caspia Grun. 5 6 1 3 2 4

Dimeregramma minor (Greg.) Ralfs 2 2Fragi/aria hyalina (Klitz.) Grun. 3 4 9 17 1 2 00 7 2 0Grammatophora oceanica (Ehr.) Grun. 4 0 1 6 1 0 0 15 6

Licmophora abbrel'iala Ag. 2 3 3 7 7 6 7L. cf. debilis (Klitz.) Grun. 5 7 J 0 3 5 7 2 1 7Mastogloia exigua Lewis 2 8 9 0 15 1 3 3M. pusil/a Grun. 18 0 20 9 1 0 0 4 8 9Nal'icula abunda Hust. 1 ]

N. aequorea Hust. 2 I I 4

N. gregaria Donkin 5 I

6N. IUI/lseni M~lIer 2 0 2 0 5 4 5

N. pmil/ardi Hust. 8 1 4 9 3 1N. pseudon}' Hust. 3 1 4

Nitzschia constricla (Greg.) Grun. t I 2

N. dissipala (Kiitz). Grun. I 1 I 3N. minlllll/a Grun. II 5 1 7 3 3N. pa/cacea Grun. 4 4 3 7 6 8 14 9

OpepllOra pacifica (Grun.) Petit 7 1 6 7 1 3 2 2 7 0Rhopafodia gibberufa (Ehr.) Mull. 42 50 4 2 1 3 4Strialella IInipllnclala (Lyngb.) Ag. 4 1 4 9Synedra affinis val'. intermedia Grun. 3 6 4 8 8 1 1 6 5

S. fasl'iculala (Ag.) Kiitz. 3 4 7

Trachysphenia acuminata Perag. I

1Total No. Individuals 1 , 0 64 1 , 0 0 3 1 , 0 0 0 3 , 067

counting and extensive SEM observations were carried out for purely taxonomic

purposes, and an additional eight taxa were encountered. These taxa were Am-phora robusta Greg., Diploneis obliqua (Brun) Hust., D. pseudovalis Hust.,Navicula amphipleuroides Hust., N. flanatica Orun., N. subforcipata Hust.,

Synedra investiens W. Sm., and Trachyneis aspera (Ehr.) CI.The four most abundant diatoms, if the three seagrass samples are pooled to

yield a single sample (N = 3067), were Fragilaria hyalina, Mastogloia pusilla,Licmophora cf. debilis, and Opephora pacifica (Table 1). For the most part,these taxa were among the four most abundant ones on each individual seagrass

species, and collectively accounted for 55.3% of all individuals counted. If allrare taxa are ignored (i.e. those represented by less than 10 individuals in each

of the three seagrass samples counted in Table 1), the taxonomic composition of

the three seagrass samples was with the exception of one taxon identical. This


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462 BULLETIN OF MARINE SCIENCE, VOL. 29, NO.4, 1979

Table 2. Species diversity (H' in bits/individual), number of taxa (S), and redundancy (R') charac-

terizing epiphytic diatom samples from Mississippi Sound (Seagrass symbols same as in Table I and

x = mean)

Statistic

H'

S

R'

HB

3.473

29

.304

CF

3.732

29

.248

IT

3.7]8

32

.276

3.641

30

.276

one exception involved Cocconeis scutellum, which was not present in the Tha-

Lassia sample of 1,000 individuals. The significance of this "taxonomic sameness"becomes apparent when it is seen that there were 18 rare taxa and the reamining

19 taxa accounted for 97.3% of all individuals counted in the three seagrasssamples (Table 1).

Table 2 presents values of three community diversity statistics characterizingeach seagrass sample. Each statistic was calculated from the data listed in TableI.Regardless of which statistic is examined the conclusion is the same; namely,

that for all practical purposes the three samples exhibited virtually equal com-munity diversity values. In addition, species diversity (H') is relatively high anddominance in the samples (R') relatively low.

Comparisons of the structural similarity of selected epiphytic diatom samples

by a selected similarity index (SIMI) appears in Table 3. Values of SIMI for allpossible sample pairs ranged from 0.825 to 0.879, or put in another way, any two

samples shared between 82 and 88% of the maximum similarity possible.

DISCUSSION

An examination of community structure characterizing epiphytic diatom sam-ples taken from three seagrass species in Mississippi Sound on 20 July 1977

revealed the following information: (1) Except for the rare taxa (2.7% of all in-dividuals counted) and the absence of Cocconeis scutellum from one sample, thetaxonomic composition of the three samples was identical. (2) Values for three

different community diversity statistics were virtually identical for the three sam-

ples indicating an inherent sameness in species-numbers relationships. (3) Com-

parison of samples by SIMI showed that the three samples were structurally verysimilar with respect not only to the kinds of taxa present but also the apportion-

ment of individuals amongst constituent taxa. Therefore, the available taxonomic

and mathematical information indicates that Halodule beaudettei, Cymodocea

filiforme, and Thalassia testudinum supported a single, nearly homogeneous epi-phytic diatom community on the above date in the seagrass beds sampled, despiteconsiderable differences in leaf morphology. Furthermore, it would appear that

the species pool for wlonization of the seagrass leaves by epiphytic diatoms is

the same for the above three angiosperms and that the absence of the rare species

from the sample counts is due to stochastic, rather than biological, processes.

Finally, even if the seagrass species are interacting nutritionally with their epi-phytes, this relationship was not significantly different between the seagrasses on20 July as no host specificity was apparent.

The questions naturally arise as to whether or not the epiphytic diatom com-

munity is largely or entirely homogeneous throughout the growing season of thethree seagrass species sampled, and what are the horizontal and vertical extents


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SULLIVAN: EPIPHYTIC SEAGRASS DIATOMS 463

Table 3. Similarity values (SIMI) for comparisons of epiphytic diatom samples from Mississippi

Sound (Seagrass symbols same as in Table I)

Compar ison

HB vs. CFHBvs. IT

CF vs. TT

SIMI

.879

.873

.825

of this possible homogeneity in community structure. At present it is not possibleto answer these questions since only three samples of epiphytic diatoms werecollected on one date from three adjacent seagrass beds. However, studies of theepiphytic flora of both marine angiosperms and macroalgae by other workers

suggest that both a temporal and spatial homogeneity may characterize the epi-phytic diatom flora of seagrasses in Mississippi Sound if a long-term, more com-prehensive study is conducted in the future. BaJlantine (1972) sampled the non-diatom algal flora epiphytic on the same three seagrass species (if synonymy istaken into account) considered here, in addition to Halophila engelmannii Asch-erson, off the west coast of Florida. Sixty-five taxa were recorded and the 20 to25 most common epiphytic taxa were collected from all seagrass species. Heconcluded that the algae simply utilized the seagrasses present in a particularlocality for attachment purposes since none showed any preference for a partic-ular host. Sullivan (1977) examined the leaves and internodes ofRuppia maritimaL. growing in New Jersey salt marsh pools and showed that a single, nearlyhomogeneous epiphytic diatom community was distributed over the entire angio-sperm host. The epiphytic diatom flora of two Sargassum species collected fromseven widespread stations in the western Sargasso Sea was studied by Carpenter(1970). Only 13 taxa could be found in the samples and except for a single station,the dominant diatom was Mastogloia binotata (Grun.) Cl. Carpenter stated fromthis and other distributional data that the epiphytic diatom flora of this large bodyof water appeared to be of a relatively homogeneous nature. Main and McIntire(1974) concluded from their work with Zostera marina and various macroalgalspecies in Yaquina Bay Estuary, Oregon that macrophytes simply increase thesurface area available to diatoms for attachment, since associations between epi-

phytic diatoms and host macrophytes were a result of similar responses to thephysical environment rather than to nutritional interactions.

The results of the preliminary study reported here represent the first publishedaccount of the epiphytic diatom flora on seagrasses in the Gulf of Mexico andtherefore is important for distributional records. Although temporal and spatialextrapolations are not justified from the data, the essential findings are in agree-ment with similar, more comprehensive, studies in the listerature. The need forfurther research in MIssissippi Sound and adjacent water masses in the Gulf ofMexico is apparent as far as the epiphytic diatoms are concerned.

ACKNOWLEDGMENTS

The assistance of Dr. L. N. Eleuterius and personnel of the Botany Section, Gulf Coast Research

Laboratory, Ocean Springs, MS i n collecting the epiphytic diatoms from the R/V HALOPHILA is

gratefully acknowledged. The work upon which Ihis report is based was supported in part by funds

provided by the United States Department of the Interior as authorized under the Water Resources

Research Act of 1964. as amended, and administered by the Water Resources Research Institute of

Mississippi.


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464 BULLETIN OF MARINE SCIENCE, VOL. 29, NO.4, 1979

LITERATURE CITED

Ballantine. D. 1972. Epiphytes of four Florida seagrass species in the Anclote Anchorage, Tarpon

Springs, Florida. M.A. Thesis, University of South Florida, Tampa. 87 pp.Carpenter, E. J. 1970. Diatoms attached to floating Sargassum in the western Sargasso Sea. Phyco-

logia 9: 269-274.

Humm, H. J. 1964. Epiphytes of the sea grass, ThaJassia testudinum, in Florida. Bull. Mar. Sci.Gulf Carib. 14: 306-341.

Main, S. P., and C. D. McIntire. 1974. The distribution of epiphytic diatoms in Yaquina Estuary.Oregon (U.S.A.). Bot. Mar. 17: 88-99.

Penhale, P. A. 1977. Macrophyte-epiphyte biomass and productivity in an eelgrass (Zostera marinaL.) community. J. Exp. Mar. BioI. Ecol. 26: 211-224.

Reyes-Vasquez, G. 1970. Studies on the diatom flora living on Tilalassia testudinum Konig in Bis-

cayne Bay. Florida. Bull. Mar. Sci. 20: 105-134.Sand-Jensen, K. 1977. Effect of epiphytes on eelgrass photosynthesis. Aquat. Bot. 3: 55-63.

Shannon, C. E., and W. Weaver. 1949. The mathematical theory of communication. Univ. Illinois

Press, Urbana. 117 pp.Stander, J. M. 1970. Diversity and similarity of benthic fauna off Oregon. M.S. Thesis. Orcgon State

University, Corvallis. 72 pp.Sullivan, M. J. 1977. Structural characteristics of a diatom community epiphytic on Ruppia maritima.

Hydrobiologia 53: 81-86.

Wood, E. J. F. 1959. Some aspects of the ecology of Lake Macquarie. N.S.W .. with regard to analleged depletion of fish. VI. Plant communities and their significance. Aust. J. Mar. Freshwater

Res. 10: 322-340.

DATE ACCEPTED: May 22, 1979.

ADDRESS: Biology Department, P.O. Drawer Gr, Mississippi State, MS 39762.
http://www.ingentaconnect.com/content/external-references?article=0007-4977(1964)14L.306[aid=8582288]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1964)14L.306[aid=8582288]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1964)14L.306[aid=8582288]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1964)14L.306[aid=8582288]http://www.ingentaconnect.com/content/external-references?article=0006-8055(1974)17L.88[aid=8665083]http://www.ingentaconnect.com/content/external-references?article=0006-8055(1974)17L.88[aid=8665083]http://www.ingentaconnect.com/content/external-references?article=0006-8055(1974)17L.88[aid=8665083]http://www.ingentaconnect.com/content/external-references?article=0022-0981(1977)26L.211[aid=8655771]http://www.ingentaconnect.com/content/external-references?article=0022-0981(1977)26L.211[aid=8655771]http://www.ingentaconnect.com/content/external-references?article=0022-0981(1977)26L.211[aid=8655771]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1970)20L.105[aid=8665082]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1970)20L.105[aid=8665082]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1970)20L.105[aid=8665082]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1970)20L.105[aid=8665082]http://www.ingentaconnect.com/content/external-references?article=0018-8158(1977)53L.81[aid=8665081]http://www.ingentaconnect.com/content/external-references?article=0018-8158(1977)53L.81[aid=8665081]http://www.ingentaconnect.com/content/external-references?article=0018-8158(1977)53L.81[aid=8665081]http://www.ingentaconnect.com/content/external-references?article=0018-8158(1977)53L.81[aid=8665081]http://www.ingentaconnect.com/content/external-references?article=0018-8158(1977)53L.81[aid=8665081]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1970)20L.105[aid=8665082]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1970)20L.105[aid=8665082]http://www.ingentaconnect.com/content/external-references?article=0022-0981(1977)26L.211[aid=8655771]http://www.ingentaconnect.com/content/external-references?article=0022-0981(1977)26L.211[aid=8655771]http://www.ingentaconnect.com/content/external-references?article=0006-8055(1974)17L.88[aid=8665083]http://www.ingentaconnect.com/content/external-references?article=0006-8055(1974)17L.88[aid=8665083]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1964)14L.306[aid=8582288]http://www.ingentaconnect.com/content/external-references?article=0007-4977(1964)14L.306[aid=8582288]

epiphytic diatoms of three seagrass species in mississippi sound (ecologia)

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