Composition and Distribution of Macrobenthic Invertebrate Fauna 



157 



low biomass (1-4 g/m 2 ) along the shelf break on 

 Georges Bank and the eastern shore of Cape Cod. 



Among the standard geographic areas, Georges 

 Bank and the Southern New England Shelf yielded 

 the highest mean densities (45 and 37/ m , re- 

 spectively) and biomass (0.20 and 0.17 g/m 2 , re- 

 spectively). 



Lower densities and biomasses occurred in the 

 Gulf of Maine and Nova Scotia shelf, and lowest 

 values for both measures occurred in the two slope 

 areas (Tables 6, 8; Fig. 155). 



Frequency of occurrence was moderately high 

 in all geographic areas with from 19 to 49% of the 

 samples containing specimens of cumaceans 

 (Table 10). 



Bathymetric Distribution 



Cumaceans were obtained at depths from 4 to 

 2,840 m. They were most plentiful, however, at 

 depths shallower than 100 m. The three depth 

 zones between and 100 m contained signifi- 

 cantly higher mean densities than the deeper zones, 

 ranging from 50 to 33/nr as depth decreased, whereas 

 in the deeper (>100 m) ones they ranged from 7 to 0.7/ 

 m 2 as depth increased to 1,999 m. In the deepest zone 

 (2,00-3,999 m) mean density was 2/m 2 (Table 11; 

 Fig. 156). 



The trend for biomass in relation to depth was simi- 

 lar to that for density but was from one to three orders 

 of magnitude lower. Mean biomass ranged from 0.26 to 



0.08 g/m 2 in waters 100 m and less in depth and was 

 lower still at deeper (>100-1,999 m) sites, ranging from 

 0.04 to 0.01 g/m 2 with increasing depth. The deepest 

 zone contained a mean biomass of 0.05 g/m 2 (Table 

 13; Fig. 156). 



Cumaceans were well represented in the samples in 

 each depth class. Four depth classes, the three between 

 25 and 200 m and the 500-999 m class, each yielded 

 specimens in over 30% of the samples (range: 30- 



