Composition and Distribution of Macrobenthic Invertebrate Fauna 



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EXPLANATION 

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11 



echinoderwata 



Figure 16 



Quantitative composition ot the total macrobenthic invertebrate fauna in 

 relation to water depth. Mean wet weight per square meter of bottom area, 

 and percentage composition, by biomass, of the major taxonomic groups 

 are shown. 



other was not uniform over the entire depth spectrum. 

 There was a 60% drop in density from 50-99 m to 100- 

 199 m and the largest drop in density occurred between 

 100 and 200 m depth.. Another way of expressing this 

 change is to say there was a decrease in density' per meter 

 increase in depth. In the vicinity of 100 m the average 

 density decreased by 18 specimens with each 1-m increase 

 in water depth. In shallower water the rate of decrease was 

 as high as 10 specimens per 1 m of water depth increase, 

 but the percentage change was substantially lower. In 

 deep water (below 200 m) the diminution rate was less 

 than one specimen per meter change in water depth. 



Differences in density in depth ranges between 1,000 and 

 1,999 m and between 2,000 and 3,999 m decreased an 

 average of 0.05 per meter increase in depth. 



Biomass diminished with depth from an average of 

 438 g/m L in shallow water to 1 1 g/m~ on the continen- 

 tal rise (Tables 13, 14; Fig. 16). The biomass remained 

 rather high (221 g or more) in shallow water out to 100 

 meters. In the vicinity of 100 m the biomass was 56% 

 lower than in the shallowest water, and 76% lower in 

 the vicinity of 500 m depth. 



The relatively high biomass, averaging 11 g/m 2 , at 

 water depths between 2,000 and 3,999 m was due in 



