Composition and Distribution of Macrobenthic Invertebrate Fauna 



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PERCENT ORGANIC CARBON 



Figure 74 



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



Average density was highest (6.8 individuals/in-) between 

 500 and 1,000 m. Density was slightly lower (3.2 to 3.5/ 

 m 2 ) in deeper water (1.000 to 2,870 m) but substantially 

 lower in depths less than 500 m (Table 11). 



Biomass ranged from to 0.03 g/nr, and the trend 

 in relation to water depth was comparable to that de- 

 scribed for density (Table 13). 



Pogonophores were present in approximately halt 

 the samples from depths greater than 500 m. In the two 

 shallower but adjacent depth classes (100-199 m and 

 200-499 m ) , there was a sharp drop in their occurrence 

 to 5 and 1 %, respectively, They were absent in the three 

 shallow depth classes (Table 15). 



Relation to Sediments 



Pogonophores were absent in coarse textured sediments 

 but were increasingly common as the sediment particle 

 size decreased from sand to silt-clay (Fig. 78). The 

 density of pogonophores was exceedingly sparse (<0.1/ 

 m 2 ) in sand sediments, intermediate in sand-silt, and 

 highest (1.9/nr) in silt-clay (Table 16). 



Their biomass was very low (<0.01 g/nr) in sand, and 

 only slightly higher in the other fine-grade sediments 

 (Table 18). 



The occurrence of pogonophores in the samples cor- 

 related very closely with average density. They were 

 exceedingly sparse (occurring in <1 %) in samples from 

 sand sediments, moderately sparse in sand-silt, and most 

 common (16%) in silt-clay substrates (Table 20). 



Relation to Water Temperature 



Pogonophores were restricted in their distribution to 

 areas that exhibited an annual bottom temperature 

 range of less than 12°C (Fig. 79). The vast majority were 

 obtained where the temperature range varied less than 

 4°C. In these waters their density averaged 1.5/m 2 and 

 the biomass averaged 0.01 g/nr (Tables 21, 23). Even 

 in areas where the temperature range was between 4° 

 and 11.9°C they were exceedingly sparse in both den- 

 sity (0.1 and 0.7/ nr) and biomass (<0.01 g/nr). 



The areas of small temperature variation (see Fig. 

 11) correspond to the deepwater regions on the conti- 



