are fed upon by a wide range of benthic 

 macrofaunal invertebrates. Many species 

 of juvenile fishes are also known to 

 ingest large numbers of meiofauna (e.g., 

 gobies, Smidt 1951; flatfish, Bregnballe 

 1961; salmonids, Feller and Kaczinski 

 1975). The transfer of meiobenthic bio- 

 mass to higher trophic levels may be 

 limited to areas where the meiobenthic 

 densities are high enough to be readily 

 consumed by bottom- feeding invertebrates 

 and vertebrates (Coull and Bell 1979). 



The macrofauna are the most well- 

 studied group of infauna because of their 

 relatively large size and the fact that 

 several species are commercially and 

 recreational ly important along the New 

 England coast (see Chapter 6). Annelid 

 worms, bivalve molluscs, and amphipod 

 crustaceans are usually the most numerous 

 although other taxonomic groups such as 

 echinoderms, hemichordates, sipunculids, 

 and nemerteans are also relatively common 

 on tidal flats. The macrofauna are often 

 divided into three generalized trophic 

 groups: (1) suspension feeders, organisms 

 that obtain food materials (e.g., plank- 

 tonic diatoms, suspended sediment) from 

 the overlying water column, (2) deposit 

 feeders, organisms dependent upon the 

 organic fractions within the sediment for 

 food, and (3) scavenger-predators, organ- 

 isms that feed mostly on dead and living 

 animal materials. These trophic groupings 

 are complicated by the feeding plasticity 

 exhibited by most species of infauna 

 (e.g., Sanders etal. 1962; Fauchald and 

 Jumars 1979; Taghon et al. 1980). Many 

 species tend to be generalized feeders 

 whose diet is primarily limited by the 

 size of the food particles they are able 

 to ingest (Whitlatch 1980). 



One feature of macrofaunal communi- 

 ties is the long recognized association of 

 particular species or assemblages of spe- 

 cies with particular sediment types. The 

 scientific literature often refers to 

 "mud" and "sand" communities rather than 

 mentioning specific species names (see 

 Figures 6 and 7). Spatial variation among 

 such species assemblages is primarily 

 correlated with sediment particle size 

 (Sanders 1958; Fager 1964; Bloom et al. 

 1972). Other factors directly or indi- 

 rectly influencing the composition of 

 bottom sediments can also affect the 



distribution patterns of macrofauna (e.g., 

 sedimentation rates, sediment stability, 

 food availability). 



The intimate association of infauna! 

 organisms with sediment features is a 

 consequence of the animals' reduced mobil- 

 ity. Infauna rely on sediments not only 

 for shelter, protection, and areas to 

 reproduce, but also for food. Deposit 

 feeders usually dominate in fine-grained 

 muddy sediments because of the increased 

 availability of detrital material and 

 microorganisms. Suspension feeders, con- 

 versely, must retain contact with the 

 sediment-water interface to feed and are 

 usually found in stable sedimentary envi- 

 ronments where there is less resuspended 

 sediment to clog their filtering struc- 

 tures. This complementary trophic group 

 separation of the benthic habitat by feed- 

 ing type while apparently true of New 

 England subtidal habitats (Sanders 1958; 

 Rhoads and Young 1970), may be less so 

 intertidally. While Whitlatch (1977) found 

 trophic separation by sediment type in 

 Barnstable Harbor, Massachusetts, Larsen 

 et al. (1979) found deposit feeders to 

 be abundant in both sand and mud flats 

 in Maine. Only unstable sandy beach 

 substrates were dominated by suspension- 

 feeding amphipods. 



In addition to conditions in the sed- 

 iment, other physical factors limit the 

 distribution of New England macrofauna. 

 On a geographic basis, distribution pat- 

 terns of macrofauna can be divided into 

 three generalized categories: (1) species 

 that occur throughout the New England 

 coast, (2) species more restricted to the 

 cold Gulf of Maine waters, and (3) species 

 found in warmer southern New England 

 waters (Appendix I). Cape Cod is recog- 

 nized as a biogeographical boundary and 

 several studies have noted distinct groups 

 of subtidal benthic species occurring only 

 north or south of Cape Cod (Yentsch et al. 

 1966). Nearshore, where water tempera- 

 tures exhibit pronounced fluctuation, 

 these categories are less distinct. North 

 of Cape Cod, warm water embayments and 

 estuaries do occur and one occasionally 

 finds warm water species in these areas 

 (e.g., the quahog, Mercenaria mercenaria ). 

 Representatives of the cold water group 

 inhabit southern New England waters espe- 

 cially during winter. Depending upon 



27 



