Composition and Distribution of Macrobenthic Invertebrate Fauna 



161 



None were present in quantitative samples 

 from the continental shelf even though pre- 

 vious studies and our own nonquantitative 

 samples have revealed their presence in cer- 

 tain habitats in the intertidal and shallow sub- 

 littoral areas along the coast. They appear to 

 be rare or absent from most of the outer conti- 

 nental shelf areas in the New England region. 



Tanaidaceans were present in only two of 

 the six standard geographic areas: Georges 

 Slope and Southern New England Slope 

 (Tables 6, 8; Fig. 161). Average density in 

 each area was 0.4 individual/m 2 with an av- 

 erage biomass of 0.01 g or less/m . 



Members of this group were present in 

 15% of the samples from Georges Slope and 

 in 9% of samples from Southern New En- 

 gland Slope (Table 10). 



Bathymetric Distribution 



In the present study tanaidaceans were found 

 only in water depths ranging from 366 to 

 3,820 m (Table 11; Fig. 162). Their density 

 was low in all depth classes within the range 

 of their occurrence but was relatively higher 

 (averaged 1 individual/m ) in depths greater 

 than 2,000 in than at shallower depths, where 

 they averaged only 0.1 of an individual/irr. 



Biomass revealed a trend similar to that of 

 numerical density. The biomass averaged 

 <0.01 g/nr in the shallower depth classes, and 

 0.01 g/m 2 in deep water (Table 13; Fig. 162). 



Frequency of occurrence disclosed trends 

 similar to both density and biomass. The 

 occurrence rate of tanaidaceans at depths 

 greater than 2,000 m was 35%, an unusually 

 high ratio compared to only 1 to 3%< occur- 

 rence in the shallower portion of their bathy- 

 metric range (Table 15). 



Relation to Sediments 



Tanaidaceans were found only in soft, fine- 

 grain sediments: sand-silt and silt-clay (Tables 

 16, 18, 20; Fig. 163). Density, biomass, and 

 frequency of occurrence were very low and 

 approximately equal in both sediment types. 



Relation to Water Temperature 

 Tanaidaceans were encountered only in areas 

 where the annual temperaMre range was less 

 than 8°C (Tables 21, 23, 25; Fig. 164). All of die 

 measures of abundance (density, biomass, and 

 frequencv of occurrence ) were very low in each 

 of die two temperaftire range classes (0°-3.9° and 

 4°-7.9°C) in which tanaidaceans occurred. 



