ley and Theroux 1981). Wet-weight biomass values between 20 

 and 30 g/nr occurred in four sediment types: Shell, silty sand, 

 gravel, and sand in order of decreasing amounts. Silt and sand- 

 gravel contained 7 and 116 polychaetes/nr, respectively, and 

 sand-shell and clay had the smallest biomass with 1.7 and 0.45 

 g/nr. In general, there were no correlations between density of 

 annelids and sediment organic carbon for the southern New 

 England area of the New York Bight. The highest biomass val- 

 ues (45.4 and 37.4 g/m 2 ) occurred in sediment with 1.5-1.9% 

 and 2.0-2.9 07 o organic content, respectively. 



Off Martha's Vineyard, mean density of combined Mol- 

 lusca was positively associated with sediment size ($) as was 

 that of pelecypods. For Georges Bank, mean density of com- 

 bined molluscs increased with percent carbon in the sediment 

 (Maurer footnote 16). Franz (1976) reported three molluscan- 

 sediment groups in northeastern Long Island Sound. One 

 group consisted of very fine sand and contained species similar 

 to that of the Mud Patch. A second and third group consisted 

 of medium sand and coarse sand and contained molluscan spe- 

 cies very similar to the sand bottom off Martha's Vineyard. 

 Based on mean grain diameter, sorting, silt-clay content, and 

 fauna, Driscoll and Brandon (1973) identified four facies in 

 Buzzards Bay. In addition, the density of particular mol- 

 luscan-sediment relationships emerged with certain feeding 

 types. Similar relationships have been reported elsewhere 

 (Maurer 1967a, b). Because of the variety of feeding types in 

 many major taxa, it is difficult to correlate major taxa with 

 sedimentary variables. This exercise is most accurately accom- 

 plished at the species level. 



Mean biomass and density of combined crustaceans were 

 negatively associated with sediment size off Martha's Vine- 

 yard. This pattern was primarily influenced by amphipods 

 and, to a lesser extent, isopods. For Georges Bank, mean den- 

 sity and biomass of amphipods were positively associated with 

 percent sand, and mean biomass declined with percent gravel 

 (Maurer footnote 16). The number of amphipod species in- 

 creased significantly with percent sand and decreased with per- 

 cent gravel, percent silt, percent silt-clay, percent carbon, and 

 percent nitrogen. In Long Island Sound, there was a strong 

 correlation in summer between Shannon-Weaver diversity of 

 benthic amphipods and sediment texture, with diversity in- 

 creasing due to decreasing species dominance, and, most im- 

 portantly, to increasing species richness as sediments became 

 coarser (Biernbaum 1979). Increased sediment instability 

 caused by winter storms resulted in marked diversity decrease. 

 The response to seasonal sediment stability by the benthic 

 biota, including amphipods, must be a critical feature influenc- 

 ing recruitment, maintenance, and production on shallow por- 

 tions of Georges Bank, including Nantucket Shoals in this 

 study area. 



Mean biomass and density of combined echinoderms were 

 positively associated with sediment type off Martha's Vine- 

 yard. This relationship was recorded for ophiuroids and holo- 

 thurians. According to Tyler and Banner (1977) there was a 

 significant relationship off the Bristol Channel between the 

 density of adult dominant ophiuroids and percent fine materi- 

 al with a weaker relationship between density and organic mat- 

 ter in the sediment. They concluded that distribution of both 

 larvae and adults correlated with the energy distribution of the 

 hydrodynamic regime. In view of the hydrodynamic regime off 

 Martha's Vineyard influencing, on the one hand, deposition in 

 the Mud Patch, and, on the other hand, extensive scouring on 



Nantucket Shoals, their findings might be applied to echino- 

 derms and the entire benthic community in the study area. 



The association between benthic animals and sediment is not 

 a simple causal relationship (Rhoads 1974). Sediment composi- 

 tion and associated physical properties (grain size, sorting, 

 porosity, mechanical strength) are primarily controlled by geo- 

 logic processes. In turn, geologic and physical oceanographic 

 processes exert considerable control over chemical properties 

 of sediment (nutrients, oxygen tension, geochemistry). Finally, 

 chemical properties catalyze and interact with biological prop- 

 erties of sediment (algal sheaths, feces, organic film, bacterial 

 and fungal slime). Because of these properties, sediment pro- 

 vides a substratum for colonization, a medium in which reside 

 temporarily or permanently, material for tube and burrow 

 construction, and a source of nutrition. Thus quantitative rela- 

 tionships between benthos and sediment parameters deserve 

 attention; however, because of the varied histories and origins 

 of the sediment parameters, the relationships are not always 

 immediately obvious in terms of their ecological significance. 

 Without quantitative chemical measures of sediment proper- 

 ties (Johnson 1974), sediment might be considered an integra- 

 tive environmental factor to which the benthos are responding. 



Faunal assemblage 



Since identification to species level was not always possible, 

 it was not feasible to quantitatively define communities in the 

 study area. Accordingly, the less formal term "assemblage" 

 was used here to designate a recurring group of organisms liv- 

 ing within broadly defined and repetitive environmental condi- 

 tions. Based on studies in the Gulf of Maine and Georges 

 Bank, four major benthic assemblages were tentatively out- 

 lined (Wigley 18 ): Sand fauna, silty-sand fauna, gravel fauna, 

 and muddy basin. Pratt (1973) elaborated on Wigley's scheme 

 and suggested that these assemblages extend along the Middle 

 Atlantic Bight. Characteristic species were recommended for 

 the sand assemblage off the Delmarva Peninsula (Maurer et al. 

 1976) which confirmed Wigley's (1968) and Pratt's (1973) pro- 

 jections. Examination of sediment data (Appendix Table 1), 

 species list (Appendix Table 2), and the distribution maps 

 presented here indicates that almost half the study area con- 

 tained the sand fauna (Echinarachnius parma, Crangon 

 septemspinosa, Chiridotea tuftsi, Pagurus acadianus, Lep- 

 tocuma minor, Haustoriidae, Phoxocephalus holbolli, Para- 

 phoxus sp., Lunatia heros, Nassarius trivittatus, Spisula soli- 

 dissima, Molgula spp.). 



The fauna of the southwestern quadrat and south central 

 portion of this study — the Mud Patch — compares well with the 

 silty-sand fauna recognized earlier by Wigley (1968) from 

 other areas on Georges Bank. The silty-sand bottom and Mud 

 Patch both contained Havelockia scabra, ampeliscids, Di- 

 chelopandalus leptocerus, Diastylis spp., Edotea triloba, 

 Scalibregma inflatum, Nephtys incisa, Cerianthus, Nucula 

 spp., Nuculana sp., Amphioplus spp., and Amphilimna oliva- 

 cea. A muddy-basin fauna between fishing banks was also 

 identified earlier (Wigley 1968). The deeper stations in this 

 study (7-10, 21, 22, 37, 38, 52, 53, 56, 57), contained species 

 that are in common with the muddy-basin fauna. For example, 



"Wigley, R. L. 1958. Bottom ecology. In Annual Report, U.S.D.I., Bur. 

 Coram. Fish., Woods Hole Laboratory, Woods Hole, Mass., p. 55-58. 



11 



