DISTRIBUTION OF MACROFAUNA WITHIN ...

BULLETIN OF MARINE SCIENCE, 33(2): 296-304,

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DISTRIBUTION OF MACROFAUNA WITHIN SEAGRASS BEDS: AN EXPLANATION FOR PATTERNS OF ABUNDANCE F Graham Lewis, III and Allan W Stoner ABSTRACT An examination of macrofaunal microhabitats within a seagrass meadow was conducted in Apalachee Bay (north Florida), Core samples were taken from two substrata within the grassbed, Thalassia testudinum shoots and bare areas among the shoots, and compared with the fauna collected in randomly placed cores. Seagrass samples showed significantly greater numbers of individuals and species than the other two treatments. When compared with either bare substrate or random samples, four times the number of individuals and twice the number of species were collected in cores containing seagrass shoots. Random samples were not significantly different from samples taken on the bare substrate. Many of the species undersampled in randomly placed cores were epifaunal and closely associated with the vegetation present, Macrobenthic species were classified according to preferred microhabitat (seagrass, bare substrate or no preference). It is suggested that macrofaunal density and species richness estimates may be greatly affected by the distribution of plants within the grassbed. This study points out potential difficulties in macrofaunal estimates when the preferred microhabitat of the species under examination is undersampled.

Coastal seagrass meadows, although long recognized as potential sources of refuge, food and nursery grounds for a variety of benthic invertebrates and fishes (Kikuchi, 1966; Kikuchi and Peres, 1977; Thayer et al., 1975; McRoy, 1977; and others), have seldom been the subject ofthe extensive quantitative investigations given to unvegetated, soft-bottom habitats. The distribution of benthic macrofauna within these seagrass beds has been restricted primarily to description of seagrass-faunal assemblages (Jackson, 1972; Marsh, 1973; 1976; Hooks et al., 1976; Thorhaug and Roessler, 1977; Heck, 1977; 1979; Nelson, 1979a; 1980). Studies have focused on the relationships of the macrofauna to both macrophyte species composition (Ledoyer, 1962; O'Gower and Wacasey, 1967; Moore et al., 1968; Santos and Simon, 1974; Heck and Wetstone, 1977; Young, 1981) and biomass (Orth, 1973; 1977; Heck and Wetstone, 1977; Brook, 1978; Stoner, 1980a; Heck and Orth, 1980). Comparatively, little information exists on the small-scale distributions of macrobenthic invertebrates within a particular seagrass habitat (Kita and Harada, 1962; Nagle, 1968; Jacobs and Pierson, 1979). In a recent paper (Lewis and Stoner, 1981), the relative efficiency of three different-sized coring devices used for sampling macrobenthos in Thalassia testudinum beds in Apalachee Bay, Florida, was examined. The smallest corer (5.5cm diameter) collected significantly greater numbers of individuals than either of the larger devices tested (7.6- and 10.5-cm diameters) when the total area (or volume) of sediment sampled by each was equal. From what is known about the life histories of species collected in seagrass meadows, the majority of individuals undersampled by the larger corers were found to be epifaunal in habit and normally observed in close association with vegetation. The increased sampling efficiency of the smaller corer was attributed to the spacing of seagrass shoots and the increased probability of randomly sampling a shoot with the greater number of small cores taken per unit surface area. The present study was designed to examine the hypothesis that the majority of macrofauna (infauna and epifauna) within a seagrass bed is closely associated with the physical structures of the seagrasses present and that estimates of mac296

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rofaunal species composition sampling strategy employed.

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297

and abundance may be greatly influenced by the

METHODS

All benthic samples were collected on 26 September 1979 from shallow turtlegrass (Thalassia testudinurn) beds in Apalachee Bay, Florida, USA. The collection site, as in the previous study (Lewis and Stoner, 1981), was located approximately 5 km southwest from the mouth of the Econfina River (permanent sampling station E12; Livingston, 1975) in approximately 1.7-2.0 m of water. Total macrophyte biomass (above- and below-ground) at the time of faunal collection, estimated with the repetitive quadrat technique of Livingston et al. (1976), was 361.4 g dry wt/m2, dominated by T. testudinurn (71.0%). Salinity and temperature were 250/00and 22.5·C, respectively. Sediment characteristics of the sampling site were given by Stoner (1980a). To examine the distribution of macrofauna within the seagrass bed, three treatments were employed: (I) diver-operated cores were taken directly over and including one Thalassia shoot (bundle sheath and blades), hereafter called seagrass samples; (2) cores were taken between but not including the Thalassia shoots, hereafter called bare substrate samples; and (3) randomly placed cores were taken which mayor may not have included a seagrass shoot, hereafter called random samples. When taking a sample which included a Thalassia shoot, the corer was lowered while the blades were gently manipulated into the sampler. The spreading of the distal portions of the blades in the water column caused some difficulty in sampling and precluded the collection of the entire plant in some cases. However, the stalk, bundle sheath and basal portions of the blades were always sampled. Three 2 X 2-m grids were located adjacent to one another in a visually homogeneous area at the sampling site; each treatment was allocated a separate sampling grid. Twenty replicate cores were taken within each grid with placement of cores based on sets of randomly generated coordinates. In the first two treatments, the nearest Thalassia shoot (seagrass sample) or nearest bare area between shoots (bare substrate) to the random coordinates was chosen for core placement. Short sections of PVC pipe with an inside diameter of 5.1 cm (surface area of 20.3 cm2 per core) were used for coring. Cores were taken to a depth of 10 cm as initial investigations on this station (Stoner, 1980a) showed that 98% of the macrofauna were found in the top 5 cm of a core. Core samples were sieved in the field with a 0.5-mm mesh screen and individually preserved in 10% buffered Formalin and rose bengal stain. Samples were hand sorted in the laboratory and all amphipods, isopods, decapods, mysids, polychaetes, molluscs and echinoderms were identified to species. Less numerous taxa, such as oligochaetes, nemerteans, cumaceans and sipunculids, were counted but not identified.

RESULTS

Species composition and abundance (individualsl20 cores) of macrofauna collected in the three treatments are shown in Table 1. One hundred and one species (20 amphipods, 38 polychaetes and 43 miscellaneous taxa) were collected in the 60 core samples. Significant differences were found among the three treatments (ANOV A with log transformation and Kruskal- Wallis one-way analysis; P < 0.01) in both numbers of individuals and species. Seagrass samples contained over four times the number of individuals and twice the number of species than the numbers recorded for either bare substrate or random samples. No differences were observed in either number of individuals or species (Duncan's multiple range test and Kruskal- Wallis multiple comparison; P > 0.10) between the latter two treatments. Although an examination of the variances of the three treatments indicated a significant departure from homoscedasticity for both numbers of species and individuals (Fmax = 6.0 and 10.1, respectively; P < 0.05), analysis of variance is robust enough to function well even with significant variance heterogeneity, if equal sample sizes are used (Box, 1954). Parametric analysis of variance and nonparametric Kruskal- Wallis tests yielded identical results. Although the sampling design precluded an estimate of variability among samples leading to a potential confounding of treatment effects with location, prior sampling suggests that the observed differences in numbers of species and individuals are due to a treatment rather than a location effect. Twelve replicate cores

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Table 1. Macrobenthic animals collected from three sampling treatments (Values represent number of individuals collected in 20 replicates) Treatments Species

Amphipoda Ampelisca vadorum Ampelisca verrilli Batea catharinensis Carinobatea carinata Cerapus sp. (cf. C. tubu/aris) Cymadusa compta E/asmopus levis Erichthonius brasiliensis Gitanopsis tortugae Grandidierella bonnieroides Lembos un/fasciatus Listriella barnardi Luconacia incerta Lysianopsis alba Melita appendiculata Ph otis macro manus Rudi/emboides nag/ei Stenothoe minuta Synchelidium americanum Tethygeneia /ongleyi Number of individuals Number of species Polychaeta Arabella iric%r Aricidea taylori Capitella capitata Capitellides jonesi Cirriformia ji1igera C/ymenel/a mucosa Diopatra cup rea Dorvillea sociabilis Eteone heterobranchia Exogene dispar Fabricia sp. Glycera americana Glycinde solitam Gyptis brevipalpa Haploscoloplos fragilis Hydroides protulicola Lumbrineris tenuis Lysidice ninetta Magelona pettiboneae Marphysa sanguinea Mediomastus californiensis Notomastus hemipodus Pectinaria gouldi Phyl/odoce fragilis Platynereis dumeri/ii Polydora socialis Pomatoceros caerulescens Prionospio heterobranchia Sabel/aria vulgaris Samythel/a sp. Scaleworrn Sigambra bassi

Seagrass

Bare Substrate

Random

8 I

5 15 3 49 12 17 4 89 6 I

I I

3

5

3

10

I

2 I

1 8

II

3 2 2

12

I

3 12 2 57 297 18 1 9 2 3

6

5

3 3 35 13

2 10 50 10

II

13

I

6 I I

5 19 20

I

2 I

3 5

3

2 2

I

2 13

II

I 7 15 I

5 2 19 14 I

4 6

16

LEWIS AND STONER: ABUNDANCE

Table I.

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Continued Treatments Species

Spio pettiboneae Spio sp. Spiophanes bombyx Streblospio benedicti Syllis corn uta Syllis sp. Number of individuals Number of species Mollusca Acanthochitona pygmaea Anachis avara Bittium varium Bivalve (juvenile) Caecum nitidum Chaetopleura apicu/ata Crepidula fornicata Cy/ichnella bidentata Hyalina veliei Lima pellucida Parvilucina multilineata Prunum apicinum Rissoina catesbyana Number of individuals Number of species Decapoda A/pheus normanni Ambidexter symmetricus Epia/tus dilatatus Hippo/yte zostericola Latreutes fucorum Pagurus mac/augh/inae Periclimenes longicaudatus Pinnixa sp. Processa bermudensis Processa vicina Shrimp larva Thor dobkini Xanthid (juvenile) N urn ber of individuals Number of species Miscellaneous taxa Apseudes sp. Bowmaniella dissimilis Cumacea Echinaster sp. Erichsonella fi/iformis Hargeria rapax Hemipho/us elongata Lightiella floridana Mysidopsis furca Nemertea Oligochaeta Ophioderma brevispinum Ophiothrix angu/ata Paracerceis caudata Pentacta pygmaea

Se.grass

2 1 2 I 22 179 31

Bare Substrate

Random

2

41 12

56 17

2 4 4 11 1 5 1 I

22 7

1 5 3 10 7 I 1 2 1 32 10

2 3 I 2 17 4 3 1 13 54 1 7 8

4 4

1 2 11 4

6

7 2

4 4

3 67 1 1

5 31

300 Table I.

BULLETIN OF MARINE SCIENCE, VOL. 33, NO.2, 1983

Continued Treatments Species

Sipunculida Turbellaria Number of individuals Number of species Total number of individuals Total number of species

Seagrass

Bare SubSlrale

Random

8 124 14 654 80

75 7 162 38

40 6 161 41

were taken at each of five adjacent sites to examine the variability among locations within the grassbed (Table 2). Variability was high among cores, yet no significant differences were observed for either numbers of species or individuals among sites (ANOY A with log transformation and Kruskal- Wallis one-way analysis; P > 0.10). Of the 80 species collected from seagrass samples, 39 (48.8%) were found exclusively in seagrass-containing cores. These species accounted for approximately 20% (132 inds.) of the total number of individuals collected in the seagrass treatment. Seven of 39 species displayed individual abundances in excess of 1% of the total number for this treatment group; these species included the amphipods Ampelisca vadorum and Elasmopus levis, polychaetes Mediomastus californiensis, an unidentified scaleworm and Syllis sp., the hermit crab Pagurus maclaughlinae and an unidentified turbellarian. Another group of 20 species was found with consistently higher numbers of individuals in the seagrass treatment than the other two treatments. This species group accounted for 62.7% (412 inds.) of the total seagrass sample. Included in this group were the amphipods Cymadusa compta, Erichthonius brasiliensis, Lembos unifasciatus, Carinobatea carinata, Lysianopsis alba, Rudilemboides naglei and Tethygeneia longleyi, the polychaetes Eteone heterobranchia, Clymenella mucosa, Exogene dispar, Fabricia sp., Notomastus hemipodus and Pomatoceros caerulescens, the chiton Chaetopleura apiculata, the decapod Processa bermudensis, the tanaid Hargeria rapax, the brittle stars Hemipholus elongata and Ophiothrix angulata, the isopod Paracerceis caudata and the unidentified nemerteans. Thus, at least 82.7% (55.7% of the overall total) of the individuals and 73.8% (60.4% of the overall total) of the species collected in the seagrass treatment were either restricted to or found almost exclusively in direct association with Thalassia shoots or sediment under the plants. In contrast, only 7 of 38 species from bare substrate samples and 12 of 41 species from random samples were found exclusively in their respective treatments. None of these species were numerically abundant, with highest individual abundance for any of these species not exceeding four individuals (Bittium varium and Caecum nitidum in the random treatment). Those species displaying greatest abundance in the bare substrate treatment included the amphipods Listriella barnardi and Synchelidium americanum and the polychaetes Haploscoloplosfragilis and Magelone pettiboneae, although all were found in low densities. None of the species collected in random samples, except those found exclusively within that sample, displayed significantly greater abundances than found in the other treatments. A small group of relatively abundant species was recorded with approximately equal frequency in all treatments; these species included the poly-

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PATTERNS OF SEAGRASS MACROFAUNA

Table 2. Number of individuals (Ind) and species (Sp) recorded per core at five sites within the Apa1achee Bay grassbed (station E12) Site I

Site 2

Site 3

Site 4

Site 5

Sample Number

Ind

Sp

Ind

Sp

Ind

Sp

Ind

Sp

Ind

Sp

1 2 3 4 5 6 7 8 9 10 11 12 Mean values

19 3 15 12 4 19 1 14 26 12 12 29 13.8

11 3 9 8 3 12 1 9 12 9 8 11 8.0

4 11 6 20 7 26 8 15 7 10 8 4 10.5

4 8 5 9 6 15 7 9 6 8 7 3 7.2

8 11 15 9 7 0 11 7 13 11 13 18 10.2

5 9 9 5 5 0 6 6 8 6 7 14 6.7

8 14 10 22 5 5 10 21 15 7 6 7 10.8

4 11 6 16 4 4 2 11 13 6 4 6 7.2

27 28 6 6 8 3 2 7 5 7 5 16 10.0

9 12 5 6 6 2 2 6 4 6 5 12 6.2

chaetes Aricidea taylori, Cirriformiafiligera, Prionospio heterobranchia and Spio pettiboneae, the caridean shrimp Hippolyte zostericola and the unidentified oligochaetes. DISCUSSION

Densities of macrofauna collected at the sampling site ranged from 3,965 individuals/m2 (random sample) to 16,108 individuals/m2 (seagrass sample), while numbers of species ranged from 38 (bare substrate) to 80 (seagrass). Clearly, both greater numbers of species and greater faunal densities were found in close proximity to seagrass shoots. Surprisingly, estimates of density and species number derived from bare substrate and random samples were nearly identical. We believe this is a result of the patchy microdistribution of Thalassia shoots which apparently were undersampled in random collections. Stoner (1980a), investigating the macrobenthos at four sites in Apalachee Bay (one unvegetated and three vegetated), noted that differences in species composition and faunal abundance were related to macrophyte biomass. Generally, species richness and density increased with increasing plant biomass at the collection sites. The present study corroborates these findings. Densities of amphipods such as Elasmopus, Lembos, Carinobatea, Luconacia and Tethygeneia (Pontogeneia in his study) which were generally found related to seagrass biomass on Stoner's sites, were observed in much higher abundances on seagrasses in this study. A similar result was noted for the polychaetes Exogene, Fabricia, Platynereis, Pomatoceros, scaleworms and Syllis and the tanaid Hargeria. All of these species appear intimately associated with the seagrass structure; whether choice of this microhabitat is obligate or facultative is unknown. Stoner (l980a) noted highest densities of capitellid worms (especially Mediomastus) at the unvegetated station, while most of the capitellids in this study were associated with seagrass shoots. It seems likely that these non-selective deposit feeders, when found within a grassbed, may concentrate under plants where organic content of the sediment may be higher, although no information is available on the distribution of sediment organic content around the plants. In this study few species were associated with bare substrate; only the polychaete Haploscoloplos was found in high enough densities to suggest a bare substrate preference. Field distribution of this species was less clear, with highest densities observed at the most vegetated of the four

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Table 3. Macrofaunal habitat preference within seagrass beds (Only those species collected in abundances of five or more individuals per habitat are included)

Seagrass

Bare substrate No preference

Amphipoda

Polychaela

Miscellaneous Taxa

Ampelisca vadorum Batea catharinensis Carinobatea carinata Cymadusa compta Elasmopus levis Erichthonius brasiliensis Lembos unifasciatus Luconacia incerta Lysianopsis alba Rudilemboides naglei Tethygeneia longleyi

Clymenella mucosa Eteone heterobranchia Exogene dispar Fabricia sp. Mediomastus californiensis Notomastus hemipodus Platynereis dumerilii Pomatoceros caerulescens Scaleworm Syllis sp.

Chaetopleura apiculata Cylich nella bidentata H argeria rapa.x Nemertea Ophiothrix angulata Pagurus maclaughlinae Paracerceis caudata Processa bermudensis Turbellaria

Haploscoloplos fragilis A ricidea taylori Prionospio heterobranchia

Hippolyte zostericola Oligochaeta

Apalachee Bay sites (Stoner, 1980a). Densities of several polychaetes, Aricidea, Prionospio, Spio pettiboneae and Cirriformia, appeared unaffected by seagrass presence both in the previous survey (Stoner, 1980a) and the present study. Densities of the caridean shrimp Hippolyte, however, were apparently contradictory between the two studies; Stoner noted density increases with increasing vegetative biomass yet the present study suggests that within a grassbed site there is no microhabitat preference. It seems reasonable to assume that while densities of macrofaunal species may be related to seagrass biomass over the large scale at different sites, within a site some species (in this study, most of the species) may prefer the specific microhabitat of the seagrass shoots while other species may show no particular selection of substrata. From this study we can identify a number of macrofaunal species with an apparent microhabitat preference (Table 3). Only those species collected in abundances of five or more individuals per habitat are included in the analysis. Some species reside on or among the seagrass blades and rhizomes, while others appear to prefer areas of bare substrate among Thalassia shoots. Whether the observed distribution pattern of these species is a result of behavioral preference, predator selection, or a combination, is unknown. Heck and Wetstone (1977) observed that greater species richness and abundance of macrofauna (primarily decapod crustaceans) were correlated with macrophyte biomass from seagrass beds in Panama. They suggested seagrasses increased faunal species number and density by increasing habitat heterogeneity, living space, food availability and predator refugia. Although these hypotheses apply equally well in the Apalachee Bay grassbeds, few tests have been performed. Limited experimental evidence suggests that some amphipods (Cymadusa compta and Melita elongata) actively seek certain vegetation (Stoner, 1980b) and that these species, and others, are more vulnerable to predation when outside the protection of the seagrass blades (Nelson, 1979b; Coen et aI., 1981; Stoner, 1982). Macrofaunal density estimates recorded from Apalachee Bay sites have been consistently low relative to investigations in other seagrass beds (Stoner, 1980a; Lewis and Stoner, 1981). Stoner (1980a) related these low densities to hydrodynamic effects, in particular, high tidal flushing rates on the shallow Apalachee Bay grass flats. He noted an average monthly macrofaunal density at station E12 of 3,107 ± 1,229 individuals/m2 (with 38 ± 6 species). Density and species richness estimates taken from bare substrate (3,990 inds.lm2 with 38 species) and random

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PATIERNS

OF SEAGRASS MACROFAUNA

303

(3,965 inds.lm2 with 41 species) treatments in the present study are comparable with those recorded previously by Stoner (1980a). Density and species number estimates derived from seagrass samples (16,108 inds.lm2 with 80 species) in the present study, however, are considerably greater than those recorded previously in Apalachee Bay and are more comparable to abundances published from other areas (Orth, 1973; Marsh, 1973; Santos and Simon, 1974). Even so, abundance estimates based exclusively on the seagrass treatment are undoubtedly overestimates because of the heterogeneous microdistribution of Thalassia shoots with areas of bare substrate among the plants. From macrophyte collections the density of shoots at the sampling site was estimated as 184 ± 26/m2• Since seagrass collections involved sampling whole shoots, an estimate of shoot density coupled with a macrofauna1 average of 32.7 individuals/shoot resulted in a total macrofaunal density of 6,017 ± 818 individuals/m2• This study points out a range of both density and species richness estimates that may be obtained when different sampling strategies are employed. At least 67% (654/977) of the individuals and 80% (80/101) of the species collected in this study were found in direct association with Thalassia shoots. With the majority of animals closely tied to the vegetation, any sampling strategy designed for macrofaunal estimates must take into account the microdistribution of the plants. In dense vegetation, standard random sampling techniques may yield more precise estimates than in areas of sparse vegetation where animals may be relatively densely packed on limited, scattered substrata. Random samples, with low numbers of replicates in sparsely vegetated habitats may result in underestimates of the fauna present. ACKNOWLEDGMENTS

The authors thank K. Brady, H. Greening and K. Leber for assistance in field collections. We thank B. Mahoney and B. Felgenhauer of Florida State University, and the anonymous reviewers for critical comments on the manuscript. Taxonomic assistance was given by K. Cairns and P. Mikkelsen of Harbor Branch Foundation, Inc. Funding was provided in part under a grant from the U.S. Environmental Protection Agency (R -8052880 I0) to Dr. R. J. Livingston, Florida State U ni versi ty. Additional support was given by the Harbor Branch Institution, Inc. Contribution No. 322 of the Harbor Branch Foundation, Inc., Fort Pierce, Florida. LITERATURE CITED Box, G. E. P. 1954. Some theorems on quadratic forms applied in the study of analysis of variance problems. I. Effect of inequality of variance in the one way classification. Ann. Math. Statist. 25: 290-302. Brook, I. M. 1978. Comparative macrofaunal abundance in turtlegrass (Tha/assia testudinum) communities in south Florida characterized by high blade density. Bull. Mar. Sci. 28: 212-217. Coen, L. D., K. L. Heck, Jr. and L. G. Abele. 1981. Experiments on competition and predation among shrimps of seagrass meadows. Ecology 62: 1484-1493. Heck, K. L., Jr. 1977. Comparative species richness, composition, and abundance of invertebrates in Caribbean seagrass (Tha/assia testudinum) meadows (Panama). Mar. BioI. 41: 335-348. --. 1979. Some determinants of the composition and abundance of motile macroinvertebrate species in tropical and temperate grass (Tha/assia testudinum) meadows. J. Biogeography 6: 183200. -and R. J. Orth. 1980. Structural components of eelgrass (Zostera marina) meadows in the lower Chesapeake Bay-decapod Crustacea. Estuaries 3: 289-295. -and G. S. Wetstone. 1977. Habitat complexity and invertebrate species richness and abundance in tropical seagrass meadows. J. Biogeography 4: 135-142. Hooks, T. A., K. L. Heck, Jr. and R. J. Livingston. 1976. An inshore marine invertebrate community: structure and habitat associations in the northeastern GulfofMexico. Bull. Mar. Sci. 26: 99-109. Jackson, J. B. C. 1972. The ecology of the molluscs of Tha/assia communities, Jamaica, West Indies. II. Molluscan population variability along an environmental stress gradient. Mar. BioI. 14: 304337.

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Jacobs, R. P. W. M. and E. S. Pierson. 1979. Zostera marina spathes as a habitat for Platynereis dumerilii (Audouin and Milne-Edwards, 1834). Aquat. Bot. 6: 403-406. Kikuchi, T. 1966. An ecological study on animal communities of the Zostera marina belt in Tomioka Bay, Amakusa, Kyushu. Publ. Amakusa Mar. BioI. Lab. 1: 1-106. --and J. M. Peres. 1977. Animal communities in the seagrass beds: a review. Pages 147-193 in C. P. McRoy, and C. Helfferich, eds. Seagrass ecosystems: a scientific perspective. Marcel Dekker, New York. Kita, T. and E. Harada. 1962. Studies on the epiphytic communities. I. Abundance and distribution of micro algae and small animals on the Zostera blades. Publ. Seto Mar. BioI. Lab. 10: 245-257. Ledoyer, M. 1962. Etude de la faune vagile des herbiers superficiels des Zosteracees et de quelques biotopes d'algues Iittorales. Recueil des Travaux de la Station Marine d'Endoume, Bull. 25, Fasc. 39: 117-235. Lewis, F. G., III and A. W. Stoner. 1981. An examination of methods for sampling macrobenthos in seagrass meadows. Bull. Mar. Sci. 31: 116-124. Livingston, R. J. 1975. Impact of kraft pulpmill effluents on estuarine and coastal fishes in Apalachee Bay, Florida, USA. Mar. BioI. 32: 19-48. ---, R. S. Lloyd and M. S. Zimmerman. 1976. Determination of sampling strategy for benthic macrophytes in polluted and unpolluted coastal areas. Bull. Mar. Sci. 26: 569-575. Marsh, G. A. 1973. The Zostera epifaunal community in the York River, Virginia. Ches. Sci. 14: 87-97. ---. 1976. Ecology of the gastropod epifauna of eelgrass in a Virginia estuary. Ches. Sci. 17: 182187. Moore, H. B., L. T. Davies, T. H. Fraser, R. H. Gore and N. R. Lopez. 1968. Some biomass figures from a tidal flat in Biscayne Bay, Florida. Bull. Mar. Sci. 18: 261-279. McRoy, C. P. 1977. Seagrass ecosystems: research recommendations of the International Seagrass Workshop. Inter. Decade Ocean. Explor. 62 pp. Nagle, J. S. 1968. Distribution of the epibiota of mac roe pibenthic plants. Contr. Mar. Sci. 13: 105144. Nelson, W. G. 1979a. An analysis of structural pattern in an eelgrass (Zostera marina) amphipod community. J. Exp. Mar. BioI. Ecol. 39: 231-264. ---. 1979b. Experimental studies of selective predation on amphipods: consequences for amphipod distribution and abundance. J. Exp. Mar. BioI. EcoL 38: 225-245. --. 1980. The biology of eelgrass (Zostera marina L.) amphipods. Crustaceana 39: 59-89. O'Gower, A. L. and J. W. Wacasey. 1967. Animal communities associated with Thalassia, Diplanthera, and sand beds in Biscayne Bay. I. Analysis of communities in relation to water movements. Bull. Mar. Sci. 17: 175-210. Orth, R. J. 1973. Benthic infauna of eelgrass, Zostera marina, beds. Ches. Sci. 14: 258-269. ---. 1977. The importance of sediment stability in seagrass communities. Pages 281-300 in B. C. Coull, ed. Ecology of marine benthos. Univ. South Carolina Press, Columbia. Santos, S. L. and J. L. Simon. 1974. Distribution and abundance of the polychaetous annelids in a south Florida estuary. Bull. Mar. Sci. 24: 669-689. Stoner, A. W. 1980a. The role of seagrass biomass in the organization of benthic macrofaunal assemblages. Bull. Mar. Sci. 30: 537-551. ---. 1980b. Perception and choice of substratum by epifaunal amphipods associated with seagrass. Mar. Ecol. Prog. Ser. 3: 105-111. --. 1982. The influence of benthic macrophytes on the foraging behavior of pinfish, Lagodon rhomboides (Linnaeus). J. Exp. Mar. BioI. Ecol. 58: 271-284. Thayer, G. W., S. M. Adams and M. W. LaCroix. 1975. Structural and functional aspects of a recently established Zostera marina community. Pages 517-540 in L. E. Cronin, ed. Estuarine research. Vol. I. Academic Press, New York. Thorhaug, A. and M. A. Roessler. 1977. Seagrass community dynamics in a subtropical estuarine lagoon. Aquaculture 12: 253-277. Young, P. C. 1981. Temporal changes in the vagile epibenthic fauna of two seagrass meadows (Zostera capricorni and Posidonia australis). Mar. EcoL Prog. Ser. 5: 91-102. DATEACCEPTED: December 30,1981. ADDRESS: Department of Biological Science, Florida State University, Tallahassee, Florida 32306. PRESENTADDRESSES:(F.G.L.) Benthic Ecology Section, Harbor Branch Institution, Inc., R.R. 1, Box 196-A, Fort Pierce, Florida 33450; (A. W.S.) Sea Education Association, P.O. Box 6, Woods Hole, Massachusetts 02543.