Composition and Distribution of Macrobenthic Invertebrate Fauna 



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 PERCENT ORGANIC CARBON 



Figure 159 

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



and 7.9°C. Biomass values, although at a much lower 

 level, were similarly affected. 



Frequency of occurrence of cumaceans in samples in 

 the various temperature range classes was fairly equal 

 (ranging from 31 to 38%) in all hut two: the 8-11.9°C 

 class had a 54% occurrence and the 0-3. 9°C class had a 

 19% rate (Tahle25). 



Relation to Sediment Organic Carbon 



Among the various taxa considered in this study, Cumacea 

 is one of only a few which showed a marked preference in 

 relation to organic carbon content. Sediments containing 

 2.00-2.99% organic carbon were clearly preferred over all 

 other content classes (Tables 26, 28; Fig. 159). There the 

 mean density of cumaceans was 123/m 2 with a mean 

 biomass of 0.24 g/rrr. reflecting, no doubt, the habit 

 adopted by many species of browsing organic matter from 

 sand grains. Another peak in abundance (25/m 2 and 0.09 

 g/m 2 ) occurred in the much lower organic carbon con- 

 tent class 0.01-0.49% Significantly lower densities and 

 biomasses occurred in the other carbon content classes, 

 and none occurred in levels above 3%. 



The highest frequency of occurrence, 44%, was in 

 the 0.01-0.49%. content class followed by the 2.00- 

 2.99% class, in which 31% of the samples yielded speci- 

 mens of cumaceans. Twelve to 29% of the samples in 

 the other content classes in which they occurred pro- 

 vided specimens (Table 30). 



Tanaidacea — Tanaidaceans are peracaridan crusta- 

 ceans generally considered to be transitory forms be- 

 tween the Mysidacea-Cumacea and the Isopoda. The 

 order is made up of four families, but only two, the 

 Paratanaidae and Neotanaidae, were represented in 

 our collections. 



Although our specimens were collected in relatively 

 deep water, tanaidaceans can be found from between 

 tide marks to ultra-abyssal depths exceeding 9,000 m. 

 They inhabit burrows, tubes, or rock crevices. Some 

 species are known to inhabit sponges; others may be 

 found on algae or the shells of bivalve mollusks, bar- 

 nacles, and other animal groups. 



Tanaidaceans attain lengths of 2 cm or more, but 

 most specimens in our samples were generally small in 

 size, usually less than 0.5 cm long. 



