benthic faunal assemblages off the delmarva peninsula

Estuarine and Coastal Marine Science (1976) 4, 163-177

Benthic Faunal Assemblages off the Delmarva Peninsula

Don Maurer, Peter Khmer, Wayne Leathem and Les Wading Marine Studies Center, College of Marine Studies, University of Delaware, Lewes, Delaware 19958, U.S.A.

Received IpJune 1974 and in revisedform 28 May 1975

Based on 90 quantitative samples collected May and November 1973 the species composition, distribution and abundance of benthic invertebrates on the inner continental shelf off the Delmarva Peninsula (38”23’N and47”r5’W) were determined. A total of 149 species were identified. Thirty-five were found only in May and 65 only in November. In May the fauna consisted primarily of nearly equal numbers of polychaete and crustacean species with an increase in the number of polychaete species and a decrease in crustacean species in November. In May the polychaetes Goniadella gracilis and Lumbrineris acuta were co-dominants (Biological Index Value) while in November the archiannelid Polygordius sp. was strongly dominant.

There was essentially no change in the number of deposit-feeding individuals from May to November. Even though the trophic structure remained unchanged, the species changed and the total number of individuals increased by 50% from May to November.

The Delmarva assemblage was briefly compared to benthic assemblages closer to the Delaware Bay estuary. Comparison revealed the importance of estuaries and ridge and swale microtopography in influencing the distribution of the shelf fauna.

It was concluded that the Delmarva assemblage belonged to a clean sand fauna which occurs throughout the inner continental shelf of the Middle Atlantic Bight. A number of species representing polychaetes, crustaceans, mollusks and echinoderms were proposed as characteristic sand fauna species.

The species composition, distribution and abundance of benthic invertebrates on the inner continental shelf off the Delmarva Peninsula (Figure I) were determined in May and

November 1973. While the benthic ecology of adjacent bays and near-shore areas has received considerable attention (reviewed by Maurer, 1974) and the continental shelf and slope areas have been studied by Sanders et al. (1965), Schopf (1965), Hessler & Sanders (1967), Hartman & Fauchald (1971), Cutler (1973) and Rex (1973), the benthos of the inner or shallow continental shelf, according to Wigley & McIntyre (1964), remains poorly known even though this area has been extensively studied for commercial species (Merrill & Ropes, 1967; Ropes & Merrill, 1970; Barker & Ropes, 1971; Musick & McEachran, 1972). Pratt (1973) provided a synthesis of research in progress on the benthic ecology of the shelf. Information on benthos in the New York Bight and off the Delmarva Peninsula is primarily

contained in unpublished reports or is limited to brief published accounts (Boesch, 1972; Leathem, et al., 1973 ; Steimle & Stone, 1973 ; Watling et al., 1974.u).

164 D. Maurer et al.

-4O*N

0 llll"

KILOMETERS

I NEW JERSEY :

’ vl 0 .... ” .:’ I :.‘..

I \\ ,:‘...‘.. /..... : 2: .., I .A.

..s i

I *'

I ..i ./ I .' C.- ,.

.' RE ./. C. /’

(1 I ./’

I I

I I I

I DE :LAWARE I / /

--- -

Pearce (1972) studied the benthos from the New York Bight, a sludge dumping area off the mouth of Delaware Bay and a control site off Bamegat Bay Inlet, New Jersey. He des- cribed the distribution patterns of 81 macrofaunal species in the New York Bight, but did not present data for the Delaware site. Thomas & Milstein (1973) reported 78 invertebrate taxa from quantitative samples 4.5 km off the southern coast of New Jersey. Leathem et al. (1973) and Watling et al. (r974a) presented brief accounts of benthic invertebrates at a dredge spoil disposal site and sewage dump site, respectively, near the mouth of Delaware Bay. Watling & Maurer (1975) reported on the trophic structure and the evenness of the

Figure I, Map showing locations of samples from IOO km site (0) and 24 kmsite (A).

Benthic fauna off the Delmarva Peninsula

benthic fauna off the Delmarva Peninsula, but the description was limited in terms of environmental variables and geographic comparisons. Boesch (1972) sampled the inner continental shelf off northern and central Virginia and presented values of diversity (H’), equitability (E), and species richness [(S-1)/[&/]. H owever, almost no description of the composition of these benthic assemblages was presented. Research by Day et al. (1971),

Cerame-Vivas & Gray (1966) and Day (1973) on the distribution of benthic faunas across the continental shelf off Cape Lookout, North Carolina represents the most complete coverage of this bathymetric range along the northern and central east coast of the United States. Species composition and abundance differed somewhat from the fauna off the Delmarva Peninsula, but some parallels exist between the two areas.

Background

The study area is approximately IOO km southeast of the mouth of Delaware Bay; its center is located at 38”23’N and 74’15’W and will hereinafter be referred to as the IOO km site. Data on bathymetry, currents, sediment, hydrography and water chemistry for this region have been reported elsewhere (Uchupi, 1968; Kester & Courant, 1973; Lear et al., 1974;

Milliman, 1972).

Methods

Forty-nine quantitive samples from nine stations in May and 41 samples from 16 stations in November 1973 (approximately five grabs per station in May and approximately three grabs per station in November) were collected by the Environmental Protection Agency with a 0.04 ms Shipek grab. Samples were not sieved aboard ship, which is a departure from conventional methods. May samples were frozen while the November samples were preserved in 10% buffered formalin. Details of methods for collecting and analyzing sediment and water quality data can be found in Palmer & Lear (1973) and Lear et al. (1974).

Before processing, the frozen samples were fixed for several days in 10% buffered formalin. In the laboratory, all samples, which were in one-gallon containers, were flushed with tap water, which overflowed onto a 0.25 mm screen, to remove the formalin. The sediment and sieve residue were placed in a shallow porcelain pan and examined for organisms under a 2X

reading glass-type magnifier. Based on this technique, estimates of density tend to be conservative. All organisms were removed with a fine paint brush and sorted for later identification.

Identifications were based on local reference collections (amphipods, isopods, hydroids) confirmed by taxonomic specialists or on reference collections from the U.S. National Museum (polychaetes) and the Delaware Museum of Natural History (molluscs). Sources for taxonomic literature can be found in Wathng & Maurer (1972a, b; 1973), Maurer & Watling (1973), Maurer et al. (1974) and Watling et al. (19743). Meiofaunal organisms (e.g. nematodes, copepods) were noted, but not counted.

Results Composition of the fauna

A total of 149 species were identified from the study area (Table I). Of these, 35 were found only in May and 65 only in November. In May the fauna consisted primarily of nearly equal numbers of polychaetes and crustacean species. There was a large increase in the number of


TABLE I. Species list of the inner continental shelf xoo km southeast of the Delaware Bay mouth for May and November 1973

Species May November

Phylum Cnidaria Bougainvillia superciliaris Agassiz Campanularia hincksi (Alder) C. neglecta (Alder) Sertularia argentea Linne Anthozoa sp. I

Phylum Rhynchocoela Nemertean sp. I Nemertean sp. z

Phylum Annelida Class Archiannelida

Polygordius sp. Class Polychaeta

Asabellides oculatus (Webster) Asabellides sp. Drilonereis longa Webster D. sp. cf. D. magna Webster and Benedict Caulleriella sp. r Caulleriella sp. 2

Chaetozone setosa Malmgren Tharyx sp. I Tharyx sp. 2

Stauronereis rudolphi (Delle Chiaje) Marphysa belli (Audouin and Milne-Edwards) Eunice sp. Pherusa afinis (Leidy) Glycera capitata Oersted G. dibranchiata Ehlers Glyceridae sp. Goniadella gracilis (Verrill) Lumbrinereis acuta (Verrill) L. coccinea (Reiner) L. fragilis (0. F. Muller) L. latreilli (Audouin and Milne-Edwards) L. sp. cf. L. tenuis (Verrill) Magelona sp. I Axiothella (Andrews) Clymenella sp. C. torquata (Leidy) C. zonalis (Verrill) Aglaophamus circinata (Verrill) Nephtys bucera Ehlers N. sp. cf. N. incisa Malmgren N. picta Ehlers Nereis grayi Pettibone Nereis sp. Ophelia denticulata Verrill Travisia carnea Verrill Orbinia ornata (Verrill) Scoloplos fragilis (Verrill) Aricidea sp. A. cerruti Laubier A. sp. cf. A. suecica El&on A. wassi Pettibone Paraonis lyra Southern Eteone heteropoda Hartman E. lactea (Claparede) Phylloa’oce maculata (Linne)

- - + + - + -t - - - - - - - + - + + + + - - + - T - - - - - - : - + - - + - + - - - + + - + - + z

+ + - + + + -

+ T t+ : - + + + - - + + + + l + + + + 1 l- ‘t; ++ + : + +’ + + + 1 1 - +

Benthic fauna off the Delmarva Peninsula 767

TABLE I. (continued)


P. mucosa Oersted Phyllodocidae sp. Harmothoe extenuata Grube H. sp. cf. H. imbricata (Linne) Euchone sp. Potamilla neglecta (Sars) Sabella microphthalma Verrill Sabellidae sp. Scalibregma inflatum Rathke Sigalion arenicola Verrill Sthenelais limicola (Ehlers) Polydora caulleryi Mesnil Prionospio steensttupi Malmgren Spiophanes bombyx (Claparede) Scoloplos squamatus (0. F. Muller) Brania sp. Exogone werugera (Claparede) Parapionosyllis longicirrata

(Webster and Benedict) Proceraea cornuta (Agassiz) Sphaerosyllis hystrix Claparede Streptosyllis arenae Webster and Benedict Syllides Zongocirrata Oersted Syllis cornuta Rathke Syllidae sp. Terebellidae sp.

Phylum Mollusca Class Gastropoda

Margarites groenlandicus (Gmelin) Lunatia heros (Say) L. triseriata (Say) Polinices duplicatus (Say) Colus pygmaea (Gould) Nassarius trivittatus (Say)

Class Bivalvia Nucula proxima Say Arctica islandica (Linne) Astarte castanea (Say) A. undata Gould Cerastoderma pinnulatum (Conrad) Cyclocardia borealis (Conrad) Lyonsia hyalina Conrad Spin& solidissima (Dillwyn) Pandora trilineata Say Cumingia sp. Ensis directus Conrad Tellina agilis Stimpson

Phylum Arthropoda Class Crustacea

Order Mysidacea Neomysis americana (S. I. Smith)

Order Cumacea Diastylis sp. Eudorellopsis deformis Kroyer Eudorella dificilis Blake Leptocuma minor Calman

Order Tanaidacea Leptochelia sp. Tanaissus lilljeborgi (Stebbing)

+ - - i- - + + - + t - - + - - f +’ - - - - - + + + - + -t + + + + - + - - + + - + +

- + - + - + -

+ i- + +

+ - - + + + f + + + + +

+ - + + + -& +

-t i

T + -

+ - + + + + f -

: + +

t

+ - + - +


TABLE I. (continued)


Order Isopoda Ptilunthuru tricarina Menzies and Frankenberg - Cirolunu concharum (Stimpson) C. impressu Harger C. politu (Stimpson) Chiridoteu urenicolu Wigley C. stenops Menzies and Frankenberg E&tea trilobu (Say) E. montosu (Stimpson)

Order Amphipoda Ampeliscu vudorum Mills A. uequicornis Bruzelius A. ugussizi Judd Byblis serrutu Smith Ampeliscidae sp. Apherusu grucilis Holmes Leptocheirns pinguis (Stimpson) Pseudunciolu obliquuu (Shoemaker) Siphonoecetes smithianus Rathbun Unciola dissimilis Shoemaker U. inermis Shoemaker U. irrorutu Say Acunthohuustorius millsi Bousfield Protohuustorius deichmannue Bousfield P. wigleyi Bousfield Hippomedon serratus Holmes Stenopleustes gracilis (Holmes) Puruphoxus spinosns Holmes Phoxocephulus hoibolli Kroyer Trichophoxus epistomus (Shoemaker) Oedicerotidae sp. Probolaides holmesi Bousfield Aeginina longicornis (Kroyer)

Order Decapoda Cancer irrorutus Say C. borealis Stimpson

Phylum Ectoprocta Alcyonidium polyoum (Hassall) Bowerbunkiu sp. cf. B. gracilis Leidy Amphiblestrum sp. Scrupuriu chelutu (Linne) Microporellu ciliutu (Pallas) Schizoporella errata Watess Porellu sp.

Phylum Entoprocta Burentsiu sp.

Phylum Echinodermata Arbuciu punctulutu (Lamarck) Echinuruchnius purmu (Lamarck) Ophiuroid sp. Asterius vulguris Verrill

Phylum Urochordata Ascidiacea sp.

+ + + + + - - + + - ;: + - - i + + - z + + + + + - + + + - + - T + - + - + + + + +

+

+ + - - + +

- +

t - - + + - - - + + - + + - - + - + - +

+ +

- + + - + + -

+

+ + + +

-

polychaete species and a decrease in crustacean species in November (Table 2). The number of species of Mollusca was similar for both sampling periods.

A method of assessing the dominance of a species in a community is the biological index value of McCloskey (1970). This value is obtained by ranking the species within each sample

Benthic fauna 08 the Delmarva Peninsula 169

on the basis of their abundance, assigning ordered values to the ranks (the highest value with the most abundant species), summing these values for each species over all samples and taking the sum for each species as a percentage of the theoretical maximum. The index value thus reflects the relative position of the species in all samples and is not influenced by very high numbers of individuals at a few stations. Tables 3 and 4 give the dominant species ordered according to their biological index values for each sampling period. In May Goniadella

gracilis and Lumbrineris acuta are essentially co-dominants (Table 3) while in November Polygordius sp. is strongly dominant (Table 4). Only fi ve of the dominant species in May are among the top ten species in November.

TABLE 2. Summary of species composition of the inner continental shelf IOO km southeast of the Delaware Bay mouth

Taxon May

Total no. % November

Total no. %

% of Total no. Total of species species

Cnidaria 2 a.4 4 3’5 5 3’3 Rhynchocoela 2 a’4

6: 0.9 2 1’3

Annelida 30 35.8 54’3 7r 47’7 Mollusca 13 15‘4 15 13.2 18 12'1

Arthropoda (Crustacea) 27 32.2 23 20'2 40 26.8

Ectoprocta 5 5'9 4 3'5 7 4‘7 Entoprocta I 0.9 I 0.7 Echinodermata 4 4'7 4 3'5 4 2'7 Urochordata

8: 1'2 I 0'7

114 149

An examination of the trophic structure of the community (Table 5) indicates that there was essentially no change in the number of deposit-feeding individuals from the May to the November samples. Also, if the omnivores are considered as potential carnivores, there is no change in the total number of carnivorous individuals. It is important to note that while the trophic structure from May to November remained unchanged, the species were considerably different (Table I) and the total number of individuals had increased by 50%.

Watling (1976) reviewed the recent uses of diversity indices and demonstrated that Fager’s (1972) scaled standard deviation measure, when applied to individuals within a trophic group, reflected the manner by which the resources available to that group were

TABLE 3. Biological index value, abundance and occurrence data for top IO species collected at the roe km site in May (49 samples)

Species

Biological Percentage Number index Total of of

Rank value individuals fauna occurrences

Goniadella gracilis I 57'7 Lumbrinereis acuta 2 55'5 Trichophoxus epistomlrs 3 51'4 Clymenella spp. 4 39'4 Echinarachnius patma Unciola iworata

2 35" 19'7

Aricidea cerruti 7 16.1 Cirolana polita 8 15’0

Byblis serrata 9 13.2 Protohaustorius wigleyi I :o 10'0

363 32'9 32 165 14.6 30

92 8.2 31 65 6.6 26

59 5’2 21

27 2'4 14 21 1'9 II

I5 1'7 13 15 1.6 9 27 1'0 7


being shared. Fager’s index (SDN) is a measure of evenness and is maximum at 1.0. When applied to deposit-feeding species, it can be seen (Table 6) that while the number of species and individuals has significantly increased, the average evenness of this trophic group has not significantly changed.

TABLE 4. Biological index value, abundance and occurrence data for top IO species collected at the IOO km site in November (41 samples)

Species



Polygordius sp. I 87.3 7,954 76.3 Exogone verugera 2 56.3 257 2’5 Trichophoxus epistomus 3 55.8 1.50 1.4 Spiophanes bombyx 4 48.2 135 1.3 Goniadella gracilis 5 48.0 326 3’1 Lumbrineris acuta 6 44.6 II8 1'1

juvenile echinoid 87 37.6 101 1'0

Echinarachnius parma 36.4 4r 0.4 Nephtys picta 9 35’4 61 0.6 Unciola irrorata IO 32.0 72 0.7

36 27 25 24 24 23 r9 20

20

r7

Comparison of shelf and bay mouth assemblages

For purposes of comparison of the IOO km site with the near-shore continental shelf in the Delaware Bay region, data for the 24 km site (Figure I) were taken from Watling et al. (1974a). At the 24 km site, the stations consisted of fine sand (<0*125 mm) on one hand and medium to coarse sand (0.25-0.5 mm) on the other. The eight fine sand stations were located near the bay mouth and along the channel area in the southern part of the sampling area. The bivalves, Nucula proxima, En& directus, Tellina agilis and Yoldia limatula were very important at these stations. The remaining 18 medium to coarse clean sand stations were dominated by Ensis directus and Nephtys picta (Table 7). It is interesting to note that only four of the dominant species from the inner shelf medium to coarse sands (Table 7) are also dominant in the similar sands of the middle shelf (Tables 3 and 4).

TABLE 5. Distribution of feeding types over all individuals collected in May and November IOO km southeast of the Delaware Bay mouth

May November

Deposit feeders No. individuals % of fauna

Carnivores No. individuals % of fauna

Omnivores No. individuals % of fauna

Scavengers No. individuals % of fauna

Suspension feeders No. individuals % of fauna

I375 2073 50’0 so.3

1163 880 42.2 21.3

98 1080 3’5 26.2

78 33 2.8 0.8

40 48 1’4 1’1

Benthic fauna off the Delmarva Peninsula

Life stage

During the examination of the May samples, there was evidence of reproductive activity. For example, the syllid polychaete, Proceraea conzuta, contained chains of female sexual buds. Specimens from November showed many examples of reproductive activity. Among specimens of an echinoid (Echinarachnius parma I) approximately 98% were less than 5 mm in diameter, which suggests that setting had occurred within six weeks of sampling (November S-IO). Many syllids were collected in various stages of reproduction; Parapionosyllis longicirrata and Exogone verugera commonly contained sexual epitokes with long swimming setae and Streptosyllis mmae also showed the swollen eyes and long setae characteristic of sexual epitokes which were unknown for this species (Pettibone, 1963). Two other polychaetes, the nephtyid, Nephtys picta, and the goniadid, Goniadella gracilis, were collected as adults in May, but commonly as juveniles in November. Approximately 75% of the adult ampeliscid amphipod, Byblis serrata, contained developing young brood pouches in November.

TABLE 6. Diversity, number of species and number of individuals of deposit- feeding trophic group from IOO km southeast of Delaware Bay mouth

SDN Station May Nov.

No. species

May Nov. No. individuals % of station fauna

May Nov. May Nov.

I

2

ii

9 II

r3 14 r7

95% Mean

0.561 0.528

0.537 0.586

0’592 0’251

0.747 0’393 0.646

0538 0.627 0.449

0.482

0.715 0.540 0.635 0.589 0.643 -

0.680 0.672 0.620 0.671 0.567

14 II I20

8 19 35 IO 7 28

14 17 64 II 21 37 8 19 98

I3 55 II ‘5 42 12 22 $3 II'2 16.4 59’7 12.6 19.8 78.8

9.8 12.9 40.6

58 I23 51

IOI

94 I39

-

98 163 103’4 128.9

77’9

51.3 74’3 67.3 58.0 36.4 80.9

49.6 44’7 61.6 75’8 30’3 42’7 71’4 - 61.7 75’4 85.2 33.6 57’2 60.7

67.9 72’9 46.5 48.3

TABLE 7. Biological index value, abundance and occurrence data for top IO species collected from stations with medium to coarse sand at the 24 km site (18 stations)

Species



Ensis directus I 49’0 ’ Nephtys picta 2 45’5 Tellina agilti 3 37’9 Cancer irroratus 4 32’3 Lumbrineris fragilis 27.8 Protohaustorius wig&i

6” 27.8

E&tea montosa 7 25.8 Trichophoxus epistomus 8 22'2

Neornysis awicana 9 21.7 Goniadella gracilis 10 20.7

(9548 64.9 IO

47 2'0 II

21 0.9 IO

22 0.9 IO

27 1’1 8 26 1’1 7 18 0.8 7 16 0.8 6

24 I’0 5 23 I’0 5

TAB

LE 8

. G

ener

a an

d sp

ecie

s of

be

nthi

c in

verte

brat

es

typi

cal

of

sand

y su

bstra

tes

from

di

ffere

nt

stud

ies

in

the

mid

dle

Atla

ntic

co

ntin

enta

l sh

elf

regi

on

Loca

tion

Sou

rce

Mid

dle

Atla

ntic

B

ight

N

antu

cket

S

hoal

s O

ff Lo

ng

Isla

nd

New

Y

ork

Big

ht

Off

Deh

narv

a P

enin

sula

G

eorg

es

Ban

k P

ratt,

19

73

Wig

ley,

19

68

Ste

imle

&

Sto

ne,

1973

P

earc

e,

1972

Th

is

stud

y W

igle

y &

S

tinto

n,

1973

Arc

hian

nelid

s an

d

Pol

ycha

etes

Aric

idea

sp

p.

Cly

men

ella

sp

p.

Gon

iade

lla

spp.

M

ageb

ma

spp.

Mah

hmop

sis

elon

gata

N

erei

s ar

enac

eodo

nta

Nep

htys

bu

cera

Ncp

htys

pi

cta

Oph

elia

sp

p.

Phe

rusa

af

inis

S

colo

plos

fra

gilis

Spi

opha

nes

bom

byx

Sth

enel

ais

limic

ola

Pel

ecyp

ods

Gas

tropo

ds

Ast

arte

ca

stan

ea

Ens

is d

irect

us

Spi

sula

so

iidis

sim

a Te

llina

agilis

Luna

tia

hero

s

Pol

inic

es

dupl

icat

us

Cly

men

ella

Gon

iade

lla

Oph

elia

Gon

iaak

lla

grac

ilis

Aric

idea

ce

rrut

i

Lum

brin

eris

fra

gilis

C

lym

enel

la

spp.

Nep

htys

sp

p.

Nep

htys

in

cisa

Sco

lopl

os

fragi

lis

Prio

nosp

io

mal

mgr

eni

Spi

opha

nes

bom

byx

Spi

opha

nes

bom

byx

Pol

ygor

dius

sp

.

Aric

idea

ce

rrut

i C

aulle

riella

sp

.

Cly

men

ella

sp

p.

Exo

gone

ve

ruge

ra

Gon

iade

lla

grac

ilis

Lum

br&

ris

acut

a

Mag

elon

a sp

p.

Nep

htys

pi

cta

Spi

opha

nes

bom

byx

Thar

yx

sp.

Arc

tica

isla

ndic

a A

rctic

a is

land

ica

Arc

tica

isla

ndic

a A

rctic

a is

land

ica

Ast

arte

ca

stan

ea

Ast

arte

ca

stan

ea

Ast

arte

ca

stan

ea

Ars

tate

ca

stan

ea

Ast

arte

un

akta

A

star

te

unak

ta

Cer

asto

derm

a pi

nnul

atum

C

eras

tode

rma

pinn

ulat

um

Cer

asto

derm

a pi

nnul

atum

C

eras

tode

rma

pinn

ulat

um

Ens

is

dire

ctus

C

yclo

card

ium

bo

real

is

Cyc

loca

rdiu

m

bore

alis

S

pisu

la

solid

issi

ma

Spi

sula

so

lidis

sim

a S

pisu

la

solid

issi

ma

Spi

sula

so

lidis

sim

a Te

llina

agilis

Col

us

pygm

aeus

Lu

natia

he

ros

Nas

sariu

s tri

vitta

tus

Col

us

pygm

aeus

Luna

tia

hero

s N

assa

rius

trivi

ttatu

s Lu

natia

he

ros

Nas

sariu

s tri

vitta

tus

Mar

garit

es

groe

nlan

dtiu

s

Pol

inic

es

dupl

icat

us

Nas

sariu

s tri

vitta

tus

Pol

inic

es

dupl

icat

us

Tabl

e 8.

(C

ont.)

Loca

tion

Sou

rce

Mid

dle

Atla

ntic

B

ight

N

antu

cket

S

hoal

s O

ff Lo

ng

Isla

nd

New

Y

ork

Big

ht

Off

Del

mar

va

Pen

insu

la

Geo

rges

B

ank

Pra

tt,

I973

W

igle

y,

I 968

S

teim

le

82 S

tone

, 19

73

Pea

rce,

19

72

This

st

udy

Wig

ley

& S

tinto

n,

1973

Am

phip

odsl

H

aust

oriid

ae

spp.

Isop

ods/

Ly

sian

assi

dae

spp.

Cum

acea

ns

Pho

xoce

phal

idae

sp

p.

Hau

stor

iidae

sp

p.

Pho

xoce

phal

idae

sp

p.

Chi

ridot

ea

Lept

ocum

a

Par

ahau

stor

ius

holm

esi

Pho

xoce

phal

us

holb

olli

Pro

toha

usto

rius

wig

leyi

Tr

icho

phox

us

epis

tom

us

Unc

iola

irr

orat

a C

irola

na

conc

haru

m

Lept

ocum

a m

inor

Dec

apod

s C

ance

r irr

orat

us

Cra

ngon

se

ptem

spin

osa

Can

cer

irror

atus

Cra

ngon

se

ptem

spin

osa

Pag

urus

ac

adia

nus

Pag

urus

lo

ngic

arpu

s

Pag

urus

po

llicar

is

Lept

oche

irus

ping

uis

Byb

lis

serra

ta

Par

ahau

stor

ius

holm

esi

Pho

xoce

phal

us

holb

olli

Pro

toha

usto

rius

wig

leyi

P

roto

haus

toriu

s de

ich-

Tr

icho

phox

us

epis

tom

us

man

nae

Unc

iola

in

erm

is

Pro

toha

usto

rius

wig

&i

Unc

iola

irr

orat

a Tr

icho

phox

us

epis

tom

us

Unc

iola

in

erm

is

Unc

iola

irr

orat

a

Ciro

lana

co

ncha

rum

C

irola

na

polit

a

Chi

ridot

ea

aren

icol

a

Lept

ocum

a m

inor

E

tirel

la

dific

ilis

Eud

orel

lops

is

defo

rmis

C

ance

r irr

orat

us

Can

cer

bore

alis

Ech

inod

erm

s E

chin

arac

hniu

s pa

rma

Ech

inar

achn

ius

parm

a A

ster

ias

forb

esi

Ech

inar

achn

ius

parm

a E

chin

arac

hniu

s pa

rma

Ast

eria

s fo

rbes

i A

ster

ias

vulg

aris

Ech

inar

achn

ius

parm

a


DiSCUSSiOn

Based on Wigley’s (1968) fauna1 divisions off New England, Pratt (1973) tentatively proposed three level bottom fauna1 groups widely distributed on the mid-Atlantic Bight continental shelf. The groups were based on sediment type (sand fauna, silt-sand fauna, silt-clay fauna), were represented by characteristic species and ranged from Cape Cod to Cape Hatteras. In view of the data base, Pratt was reluctant to depict definite boundaries among the proposed faunal groups. To examine the general applicability of Pratt’s proposed sand fauna, characteristic species from several geographic areas along the shelf were obtained from the literature and summarized in Table 8. Care was taken to cite species which were quantitatively collected, were abundant or characteristic of the geographic area and occurred within a depth range and sediment type similar to Pratt’s guidelines.

Inj?uence of habitat andgeographic area

In Pratt’s (1973) initial scheme the sand and the silty-sand faunas were separated. He acknowledged that while silty-sands contained much less than the 25% silt typical of that category, these sediments possessed more organic matter than the clean sands. The silty sands also were often covered by a thin layer of flocculent material. For these reasons he suggested that the clean sands were mobile and the silty-sands were stable.

There is reason to suggest that in certain cases, the fauna at a given site is composed of species representing various habitat types, i.e. sand, silt-clay, marine, estuarine. For example, we suspect that the distribution of Mercenaria mercenaria reported for the New York area (Pearce, 1972; Steimle & Stone, 1973) is attributable to the influence of the semi-enclosed bays and estuaries of Long Island and New Jersey which contain high densities of this species. Moreover, the addition of organic load to the New York Bight has changed the sediment type in some areas. Pollution problems together with estuarine influences make the apex (northern part) of the New York Bight atypical in the progression of fauna1 types. In another example, the species at the 24 km site (Figure I) reflect differences in sediment, marine and estuarine conditions. Species living in sand (Goniadella gracilis, Spiophanes bombyx, Protohaustorius wigkyi) are similar to Pratt’s sand fauna, while those in depressions with silty-sand or mud (Nucula proxima and Yoldia limatula) are similar to his silty-sand or stable sand fauna.

It has recently been noted from bottom still and television pictures (Don Lear, H. D. Palmer and J. Foms, personal communication) that the ridge and swale microtopography (Swift et al., 1973) of this region may strongly influence the sediment composition. Over much of the area sand waves of 3c-100 cm wavelength and 2-5 cm height were common. The crests (ridges) were clean and dominated by Echinurachnius parma, whereas the troughs contained much shell and flocculent material. It is likely, therefore, that the sand and silty- sand faunas are essentially continuous and should be considered as one fauna1 unit until controlled sampling and cluster techniques can be used to differentiate them.

The importance of estuaries markedly influencing the composition of species on the inner continental shelf also should be recognized. Depending on the size of an estuary and its effect, the influence will vary accordingly, which in the case of Delaware Bay, may extend 15-30 km off the bay mouth. At the 24 km site, the influence of the Delaware Bay may be seen in the sediment. Along the southern part of the sampling area and closest to the bay mouth the sediment contains 30-337~ silt-clay. Further from the mouth of the bay along the same southerly line, the percentage of silt and clay decreased markedly to approximately 1%.

Benthic fauna off the Delmarva Peninsula 175

Characteristic sandfauna species

The distribution of the polychaetes found in this study conforms well with Pratt’s proposed sand (and silty-sand) fauna, although we believe that species of syllids, paraonids and cirratulids should also be cited as characteristic of this group (Table 8). Several molluscs, especially the bivalves, Cerastoderma pinnulatum, Cyclocardium ( = Venericardia) borealis and the gastropods, Coluspygmaeus and Nassarius trivittatus, occur widely enough (Table 8) to be added to Pratt’s list.

Pratt indicated the importance of haustorid, phoxocephalid and lysianassid amphipods for the sand fauna, but did not suggest particular species. From the species listed in Table 8, we found the amphipods, Protohaustorius wigleyi, P. deichmannae, Trichophoxus epistomus,

Phoxocephalus holbolli, Unciola irrorata, U. inermis, Byblis serrata, Leptocheirus pinguis and the isopods, Cirolana polita, C. concharum, Chiridotea arenicola, to be representative. Other crustaceans and echinoderms listed in Table 8 could also be added. Since Polygordius sp. was the most abundant species, it was included in Table 8 even though it has not been frequently reported. Day et al. (1971) commented that a new species of Polygordius was very abundant on the inner shelf off North Carolina and a new species of Polygordius was also recorded off Long Island (D. K. Serafy, personal communication). Whether these areas contain the same species or closely related species is presently unknown, but it appears that species of this genus might be considered characteristic of the sand fauna.

Community structure

The large change in the species composition of this community accompanied by little change in the percentage of the fauna in each trophic group and in the evenness of the deposit- feeding species suggests that the structure and organization of this assemblage may be quite stable even though the species composition may fluctuate widely. If the organization of the community remains constant, seasonal fluctuations in energy input levels would result in proportionate rather than disproportionate changes in energy flow through major transfer routes and the trophic analysis of this assemblage should be continued over a longer time scale.

Acknowledgements

We would like to thank our associates, Mr Jeff Tinsman and Mr Henry Lind, for their efforts in sorting samples. This research was supported in part by the Delaware River and Bay Authority and the Environmental Protection Agency (EPA). Dr Don Lear, EPA, and his colleagues, Mrs Susan Smith and MS Maria O’Malley, provided us with samples, background information, and encouragement. Drs Sheldon Pratt, Donald Boesch and Jack Pearce generously shared their constructive comments and extensive experience with us.

References

Barker, A. M. & Ropes, J. W. 1971 The Atlantic surf clam fishery 1969. Commercial Fisheries Review 33, (6) 35-42.

Boesch, D. F. 1972 Species diversity of marine macrobenthos in the Virginia area. Chesapeake Science x3,206-211.

Cerame-Vivas, M. J. & Gray, I. E. 1966 The distributional pattern of benthic invertebrates of the continental shelf off North Carolina. Ecology 47(2), 260-270.

Cutler, E. B. 1973 Sipunculida of the western North Atlantic. Bulletin of the American Museum of Natural History I52(3), 107-204.


Day, J. H. 1973 New polychaeta from Beaufort with a key to all species recorded from North Carolina. National Marine Fisheries Service Circular No. 375, 140 pp.

Day, J. H., Field, J. G. & Montgomery, M. P. 1971 The use of numerical methods to determine the distribution of the benthic fauna across the continental shelf of North Carolina. Journal of Animl Ecology 40,93-123.

Fager, E. W. 1972 Diversity: a sampling study. American Naturalist 106,293-3 IO. Hartman, 0. & Fauchald, K. 1971 Deep-water benthic polychaetous annelids off New England to

Bermuda and other North Atlantic areas. Part II. AClan Hancock Monograph in Marine Biology 6, I-327.

Hessler, R. R. & Sanders, H. L. 1967 Fauna1 diversity in the deep-sea. Deep-Sea Research 1~65-78. Kester, D. R. & Courant, R. A. 1973 A summary of chemical oceanographic conditions. In: Coastal and

Offshore Environmental Inventory: Cape Hatteras to Nantucket Shoals. Marine Publication Series No. 2, University of Rhode Island.

Lear, D. W., Smith, S. K. & O’Malley, M. L. 1974 Environmental survey of two interim dumpsites Middle Atlantic Big& 141 pp. United States Environmental Protection Agency, Region III, Philadelphia, Pennsvlvania.

Leathem, W., Kinner, P., Maurer, D., Biggs, R. & Treasure, W. 1973 Effect of spoil disposal on benthic invertebrates. Marine Pollution Bulletin q(8), 122-12s. _.

Maurer, D. 1974 Biological condition of the deepwater portion of lower Delaware Bay. A Report &r rhe National Science Fouruiation RANN Program 94 pp.

Maurer, D. Sz Watling, L. 1973 Studies on the oyster community of Delaware: The influence of the estuarine environment on the associated fauna. Internationale Revue der Gesamten Hy&obi&gie 58(2),161-201.

Maurer, D., Watling, L. & April], G. 1974 The distribution and ecology of common marine and estuarine pelecypods in the Delaware Bay area. Nautilus 88(z), 38-45.

McCloskey, L. R. 1970 The dynamics of the community associated with a marine scleractinian coral. Internationale Revue des Gesamten Hydrobiologie 55, I 3-8 I.

Merrill, A. S. & Ropes, J. W. 1967 Distribution of southern quahogs off the Middle Atlantic coast. Commercial Fisheries Rev& 29(4), 62-64.

Milliman, J. D. 1972 Atlantic continental shelf and slope of the United States-petrology of the sand fraction of sediments, northern New Jersey to southern Florida. United States Geological Survey Professional Paper 529-J, 40 pp.

Musick, J. A. & McEachran, J. D. 1972 Autumn and winter occurrence of decapod Crustacea in the Chesapeake Bight, U.S.A. Crustaceana 22(z), 190-200.

Palmer, H. D. & Lear, D. W. 1973 Environmen tal survey of an interim ocean dumpsite, Middle Atlantic Bight 134 pp. United States Environmental Protection Agency, Region III, Philadelphia, Penn- sylvania.

Pearce, J. B. (Ed.) 1972 Section 2: Benthic studies. The effects of waste disposal in the New York Bight. Final Report. Report to the United States Coastal Engineering Research Centre from National Marine Fisheries Service Sandy Hook Laboratory, New Jersey.

Pettibone, M. H. 1963 Marine polychaete worms of the New England region. I. Aphroditidae through Trochochaetidae. Bulletin U.S. National Museum 2~7~1-356.

Pratt, S. D. 1973 Benthic fauna. In: Coastal and offshore environmental inventory Cape Hatteras to Nantucket Shoals. Marine Publication Series No. 2, University of Rhode Island.

Rex, M. A. 1973 Deep-sea species diversity: decreased gastropod diversity at abyssal depths. Science 182, 1051-1053.

Ropes, J. W. & Merrill, A. S. 1970 The distribution and density of the surf clam, Spisula solidissima. Annual Report of the American Malacological Union pp. 20.

Sanders, H. L., Hessler, R. R. & Hampson, G. R. 1965 An introduction to the study of deep-sea benthic faunal assemblages along the Gay Head-Bermuda transect. Deep-Sea Research 12,845-867.

Schopf, T. J. M. 1965 Ectoproct (Bryozoa) distribution on the Atlantic continental shelf from the Hudson Canyon to Nova Scotia. Biological Bulletin x29,421-422.

Steimle, F. W. & Stone, R. B. 1973 Abundance and distribution of inshore benthic fauna off south- western Long Island, New York. Technical Report, National Marine Fisheries Service SSRF-673, 50 PP.

Swift, D. J. P., Duane, D. B. 8z McKinney, T. F. 1973 Ridge and swale topography of the Middle Atlantic Bight, North America; secular response to the Holocene hydraulic regime. Marine Gedogyq,227-247.

Thomas, D. L. & Milstein, C. B. 1973 Ecological Studies in the Bays and Other Waterways near Little Egg Inlet and in the Ocean in the Vicinity of the Proposed Site for the Atlantic Generating Station, NewJersey. Part I, 666 pp. Ichthyological Associates, Inc.

Uchupi, E. 1968 Atlantic continental shelf and slope of the United States-Physiography. United States Geological Survey, Professional Paper 529-I, 44 pp.

Benthic fauna off the Delntarva Peninsula I77

Watling, L. 1976 Analysis of structural variations in a shallow estuarine deposit-feeding community. Journal of Experimental Marine Biology and Ecology (in press).

Watling, L. & Maurer, D. r97aa Marine shallow water amphipods of the Delaware Bay area, U.S.A. Crustaceana Supplement 3,251-266.

Watling, L. & Maurer, D. x9723 Shallow water hydroids of the Delaware Bay region.rournaZ of Natural History 6,643449.

Watling, L. & Maurer, D. 1973 Guide to the Macroscopic Estuarine and Marine Invertebrates of the Delaware Bay Region. College of Marine Studies, University of Delaware, 178 pp.

Watling, L. & Maurer, D. 1975 An evaluation of the mid-Atlantic Bight inner continental shelf benthic assemblages. In: Marine Environmental Implications of Offshore Oil and Gas Development in the Baltimore Canyon Region of the mid-Atlantic coast. Proceedings Conference and Workshop, Estuarine Research Federation (in press).

Watling, L., Leathem, W., Kinner, P., Wethe, C. & Maurer, D. 1974a An evaluation of sewage sludge dumping on the benthos off Delaware Bay. Marine Pollution Bulletin s(3), 39-42.

Watling, L., Lindsay, J., Smith, R. & Maurer, D. 1974b The distribution of Isopoda in the Delaware Bay region. Internationale Revue der Gesamten Hydrobiologie 59(3), 343-35 I.

Wigley, R. L. 1968 Benthic invertebrates of the New England fishing banks. Underwater Naturalist 58-13.

Wigley, R. L. & McIntyre, A. D. 1964 Some quantitative comparisons of offshore meiobenthos and macrobenthos south of Martha’s Vineyard. Limnology and Oceanography 9,485-493.

Wigley, R. L. & Stinton, F. C. 1973 Distribution of macroscopic remains of recent animals from marine sediments off Massachusetts. Fishery Bulletin 71(1), 1-40.

benthic faunal assemblages off the delmarva peninsula

Documents