Composition and Distribution of Macrobenthic Invertebrate Fauna 



177 



Average biomass ranged from slightly over 

 3 g/m 2 on Georges Bank to 0.02 g/m 2 on 

 the Southern New England Slope (Table 8; 

 Fig. 185). In the other areas, biomass ranged 

 from 0.6 to slightly over 2 g/m 2 . 



Frequency of occurrence of decapods in the 

 samples was moderately high on Georges Bank, 

 Southern New England Shelf, and off Nova 

 Scotia, ranging from 46 to 18% (Table 10). 

 Their occurrence in samples from the Gulf of 

 Maine and Southern New England Slope was 

 considerably lower, 6 and 3%, respectively. 



Bath y metric Distrib it tio n 



Decapods were almost wholly restricted to 

 water depths of less than 500 m and showed 

 a general trend of diminishing in abundance 

 as water depth increased (Table 1 1 ; Fig. 186). 

 Average densitv was highest ( 18/m 2 ) in the 

 shallowest depth-range class (0-24 m) and 

 dropped to 50% and less of this value in the 

 continental shelf depth classes between 25 

 and 200 m. Density in the upper slope depth 

 class (200-499 m) was low (0.3/m 2 ) and 

 very low (0.1/rrr) in the only deepwater 

 depth class (1,000-1,999 m) in which they 

 occurred. 



Average biomass generally followed the 

 trend established for densitv (Table 13; Fig. 

 186). In the shallow-water depth class, aver- 

 age biomass was nearly one and one half to 

 three times (3.3 g/m 2 ) higher than that in 

 the continental shelf depth classes where it 

 ranged from 1.1 to 2.1 g/m 2 . Biomass was 

 0.61 g/m 2 in the upper slope depth class 

 (200-499 m ) but only 0.03 g/m 2 in the deep- 

 est class in which decapods occurred ( 1000- 

 1999 m). 



Decapod frequency of occurrence in the 

 samples was fairly uniform at moderate lev- 

 els (35 to 39%) in the three depth classes 

 <99 m, moderately low (13%) in the shelf 

 edge class, and low (3 and 4%) in the other 

 two classes they occupied (Table 15). 



Relation to Sediments 



Decapods were present in all sediment types except till. 

 Both density and biomass diminished with decreasing 

 sediment particle size (Tables 16, 18; Fig. 187). Gravel 

 bottoms contained the greatest average number (24/ 

 m 2 ) of decapods as well as greatest biomass (5.56 g/ 

 m 2 ). A drop in density occurred in shell and sand, each 

 of which yielded an average of 9/m 2 , nearly three times 

 fewer decapods, but biomass diminution was not as 

 dramatic in shell which contained an average of 4.78 g/ 



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25 50 100 200 500 1000 2000 4000 



WATER DEPTH IN METERS 



Figure 186 

 Density and biomass of Decapoda in relation to water dt 



pth. 



m z ; however, sand contained nearly five times less bio- 

 mass (1.16 g/m 2 ) than gravel. Sand-silt and silt-clay, the 

 finest sediments, yielded lower density and biomass. 



Frequency of occurrence of decapods was moderate 

 and uniform in samples in gravel, shell, and sand, rang- 

 ing from 33 to 37%, but was relatively low in sand-silt 

 and silt-clay, 7 and 4%, respectively (Table 20). 



Relation to Water Temperature 



Average density and biomass of decapods showed a ten- 

 dency to increase with broadening temperature range to 



