Composition and Distribution of Macrobenthic Invertebrate Fauna 



175 



slow-moving pagurid hermit crabs. Size of brachyuran 

 crabs averaged between 15 and 20 mm carapace width; 

 the two species of Cancel- did provide some larger speci- 

 mens in the 50 to 60 mm range, and Pinnixa spp. provided 

 some of the smaller specimens in the 5 to 6 mm range. 



Colors of decapods in our samples ranged from the 

 nearly transparent or translucent white of Crangon to 

 the dark reddish browns and blacks of Hyas. A veritable 

 spectrum of colors was represented between these ex- 

 tremes, ranging from the delicate flesh and pink hues 

 of the pandalid shrimps, to the tans, greens, blues, and 

 grays and muted reds of the pagurid and brachyuran 

 crabs. Most colorful were the bright red-orange Geryon 

 quinquedens. 



The decapods as a group are similar to 

 bivalves in providing a broad spectrum of 

 prey to a variety of predators. In addition to 

 man, whose harvests of lobsters, shrimps, 

 and crabs are well known, many other ma- 

 rine animals (including other invertebrates, 

 mammals, birds, and fishes) depend on de- 

 capod prey for a substantial portion of their 

 sustenance. 



Decapods occurred in 246 samples (23% 

 of the total). Their density averaged 8 indi- 

 viduals/m 2 , and their biomass 1.32 g/m 2 

 (Table 5). 



Geographic Distribution 



The most striking feature of decapod distri- 

 bution revealed by our samples was their 

 apparent absence from large portions of the 

 Gulf of Maine (Fig. 184). This artifact is due 

 primarily to sampling gear bias since, tradi- 

 tionallv, this region has been well known for 



the high annual yields of lobsters and shrimps. How- 

 ever, low densities were recorded from the northeast 

 corner of the Gulf at the entrance to the Bay of Fundy, 

 the Western Basin section north of Great South Chan- 

 nel, and some inshore localities. Low densities (1-49 

 individuals/ m ) also prevailed over most of their range 

 elsewhere on the continental shelf in the study area. 

 Moderate (50-99/m 2 ) and high (100-266/m 2 ) average 

 densities were restricted to small patches on Georges 

 Bank and in Nantucket and Vineyard Sounds and at the 

 head of Long Island Sound. 



Average biomass of decapods was low (<0.1 to 9.9 g/ 

 m 2 ) over the major portion of their range; there were 

 only a few small patches of moderate (10-50 g/m 2 ) 



O O NUMBER 



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0-39 4-79 1-119 12-159 16-199 20-239 



ANNUAL RANGE IN BOTTOM WATER TEMPERATURE 



IN DEGREES CELSIUS 



Figure 182 

 Density and biomass of Mvsidacea in relation to the annual range 

 of bottom water temperature. 



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 PERCENT ORGANIC CARBON 



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Figure 183 



Density and biomass of Mysidacea in relation to sediment organic carbon. 



