Pelecypoda. — Mean biomass of pelecypods ranged from 0.1 

 to > 100 g/m 2 . Highest values were recorded directly south of 

 Nantucket Shoals and Nantucket I. (Maurer and Wigley foot- 

 note 6). A range of 20-80 m, 6.0°-9.9°C, <|> 2.0-3.9, and 0-20% 

 silt-clay comprised the main biomass distribution (Fig. 6). 



Density patterns differed from biomass patterns because of 

 size differences. A range of 40-200 m, 6.0°-10.9°C, <|> 3.0-5.9, 

 and 20-100% silt-clay comprised the main density distribution. 

 There was a significant negative association between pelecy- 

 pod biomass and temperature and depth, and a positive asso- 

 ciation between density and sediment size. Species of bivalves 

 showed marked differential distribution. Arctica islandica and 

 Cerastoderma pinnulatum mainly occurred at depths shal- 

 lower than 80 m and in sand with <20% silt-clay. In contrast, 

 Cuspidaha striata, C. perrostrata, and Bathyarca pectunculoi- 

 des occurred almost exclusively at depths > 150 m in sediment 

 wit.. >50% silt-clay. Molluscan biomass distribution was 

 chiefly influenced by the distribution of the pelecypod A. 

 islandica. Small species of bivalves contributed significantly to 

 the density pattern of Mollusca. 



Crustacea 



In terms of biomass and density, the Crustacea contained 

 Decapoda (5.7 and 0.2%, respectively), Cumacea (1.3 and 

 2.1%), Isopoda (5.0 and 1.0%), and Amphipoda (88 and 

 96.7%). Mean biomass and density of crustaceans ranged 

 from 0.1 to >50 g/m 2 and from 1 to > 1,000/m 2 . A depth 

 range of 20-80 m, 6.0°-9.9°C, $ 1.0-3.9, and 0-20% silt-clay 

 comprised the main distribution of crustacean biomass and 

 density (Fig. 6). Mean biomass and density were negatively 

 associated with depth (R = -0.53,/?= -0.56), sediment size 

 (R = -0.31, R = -0.30), and bottom temperature (R = 

 -0.48, R = -0.50). 



Decapoda. — Mean biomass and density of decapods ranged 

 from 0.1 to 49 g/m 2 and from 10 to 25/m 2 . Their distribution 

 was sporadic (Maurer and Wigley footnote 6), but grab 

 samples are not the most effective way to collect large crusta- 

 ceans. Crangon septemspinosa, Pagurus pubescens, Cancer 

 spp., and Pandalus spp. were collected frequently. Crangon 

 septemspinosa occurred at depths <20 m to >200 m. In con- 

 trast, Hyas sp., Euprognatha sp., Munida sp., and Geryon sp. 

 were generally collected deeper than 100 m. 



Cumacea. — Mean biomass and density of cumaceans ranged 

 from 0.1 to 1.0 g/m 2 and from 1.0 to >400/m 2 . Cumaceans 

 occurred widely and were relatively evenly spread, occurring 

 mainly at lower densities of 1-100/m 2 (Maurer and Wigley 

 footnote 6). Characteristic species included Diastylispolita, D. 

 quadrispinosa, Eudorella emarginata, Leptostyllis sp., Eu- 

 dorellopsis sp., and Leptocuma sp. A depth range of 20 m, 

 7.0°-8.9°C, <j> 3.0-3.9, and 0-10% silt-clay comprised the main 

 biomass distribution, whereas the main density distribution 

 was most accurately contained in a depth range of 20-40 m, 

 6.0°-8.9°C, <|> 2.0-3.9, and 0-20% silt-clay (Fig. 6). Mean bio- 

 mass and density of cumaceans were negatively associated with 

 depth (R = -0.36, R = -0.52), and density with tempera- 

 ture CR = -0.29). 



Isopoda. — Mean biomass and density ranged from 0.1 to 10 

 g/m 2 and from 1 to > 100/m 2 . The greatest numbers of isopods 



occurred between 40 and 60 m throughout most of the study 

 area, but between 60 and 80 m directly south of Nantucket 

 Shoals (Maurer and Wigley footnote 6). Biomass and density 

 patterns were essentially the same. Characteristic species were 

 Cirolana polita, Chiridotea tuftsi, Ptilanthura tenuis, Edotea 

 triloba, and Calathura sp. Mean density of isopods was 

 negatively associated with depth (R = -0.38), sediment size 

 {R = -0.38), and temperature (# = -0.26). 



Amphipoda. — Mean biomass and density of amphipods 

 ranged from 0.1 to >50 g/m 2 and from 1 to > 1,000/m 2 . The 

 shallow water portion mostly contained densities > l,000/m : . 

 There was a sharp decline in biomass and density below 100 m 

 (Maurer and Wigley footnote 6). Characteristic amphipod 

 taxa were Leptocheirus pinguis, Unciola irrorata, Caprella 

 spp., Coropium spp., ampelescids (including Ampelisca cotn- 

 pressa, A. macrocephala, and Byblisserratd), phoxocephalids, 

 photids, and haustoriids. A depth range of 20-80 m, 

 6.0°-9.9°C, <(> 1.0-3.9, and 0-40% silt-clay comprised the main 

 distribution of biomass. These ranges were the same for densi- 

 ty except for depth with a range of 20-100 m (Fig. 6). The dis- 

 tribution of amphipod biomass and density greatly influenced 

 the same patterns for combined Crustacea. Mean biomass and 

 density were negatively associated with depth (R = -0.53, 

 R = -0.54), sediment size (R = -0.31, R = -0.31), and 

 temperature (/? = -0.49, R = -0.51). 



Echinodermata 



In terms of biomass and density, echinoderms contained 

 Ophiuroidea (21.7 and 78.6%, respectively), Holothuroidea 

 (52.9 and 5.9%), Echinoidea (19.7 and 13.8%), and Asteroi- 

 dea (5.7 and 1.7%). Mean biomass and density ranged from 

 0.1 to >100 g/m 2 and from 1 to > 1,000/m 2 . Biomass and 

 density patterns of echinoderms were generally dissimilar (Fig. 

 6). Mean biomass and density were positively associated with 

 depth (R = 0.27, R = 0.25), sediment size (R = 0.44, 

 R = 0.36), and temperature (R = 0.33, R = 0.42). 



Ophiuroidea. — Mean biomass and density of ophiuroids 

 ranged from 0.1 to >100 g/m 2 and from 1 to >500/m 2 . 

 However, in general, biomass values of 0.1-49 g/m 2 were most 

 common, as were densities of 1 to >500/m 2 . Characteristic 

 species were Amphilimna olivacea, Amphioplus abditus, A. 

 fragilis, Axiognathus squamatus, and Ophiura sarsi. In terms 

 of biomass, ophiuroids were mainly restricted to depths >80 

 m, 10.0°-12.9°C, + 4.0-5.9, and 20-100% silt-clay, and for 

 density 7.0°-12.9°C and <)> 3.0-5.9 (Fig. 6). Mean biomass and 

 density were positively associated with depth (R = 0.44, R = 

 0.40), sediment size (R = 0.36, R = 0.40), and temperature 

 (R = 0.54, R = 0.48). 



Holothuroidea. — Mean biomass and density of holothur- 

 ians ranged from 0.1 to > 100 g/m 2 and from 1 to 399/m 2 . 

 Holothurians were almost exclusively collected in the deeper 

 portion of the study area below 80 m (Maurer and Wigley 

 footnote 6). Characteristic species were Synapta sp., 

 Astichopus sp., Molpadia sp., and Havelockia scabra. A 

 depth range of 40-100 m, 6.0°-7.9°C, <j> 3.0-4.9, and 20-80% 

 silt-clay comprised the main biomass distribution, whereas a 

 depth range of 80-100 m and 6.0°-10.9°C comprised the main 

 density distribution (Fig. 6). 



