THE BARENTS SEA 147 



Brisaster fragilis (on the average 60 per cent of the total biomass) is the 

 dominant form of this community. Among the characteristic forms one may 

 point out the molluscs Astarte crenata ; of the echinoderms Ctenodiscus crispa- 

 tus, Leptychaster arcticus, Ophiura sarsi, Trochostoma boreale; among the 

 polychaetes Asychis biceps, Myriochele oculata, Owenia assimilis, Spiochaetop- 

 terus typicus, Praxilella praetermissa, crustaceans Pandalus borealis and Hyas 

 coarctatus, and the brachiopods Waldheimia cranium and Terebratulina caput- 

 serpentis. 



The vast Spitsbergen shallow, extending southwards to 74° N latitude in its 

 central part and especially between Bear Island and Nadezhda Island, is less 

 than 50 m deep and has a hard floor. Sections of cleanly washed pebble and 

 deposits of broken shells and fragments of Balanus with a small admixture of 

 sand are extremely unfavourable for the development of life. The benthos 

 biomass is here calculated (M. Idelson, 1930) as a few grammes or even frac- 

 tions of a gramme per m 2 . The population consists of small bivalves and 

 gastropod molluscs, polychaetes and crustaceans. In areas where the sea-bed 

 has finer structure, the epifauna is fairly abundant, forming sometimes 

 hundreds and even thousands of grammes per m 2 mainly consisting of Cucu- 

 maria frondosa, Strongylocentrotus droebachiensis, Balanus balanus and 

 Alcyonidium gelatinosum. Only Cyprina islandica is distinguished by its bio- 

 mass among the infauna. On the silty sand and sandy silt bottoms surround- 

 ing Spitsbergen shallow from the east and south dwells the fauna described 

 above in other communities. 



Porifera and Brisaster communities extending from the northwest are re- 

 placed by communities peculiar to the western trough, which is 400 m deep 

 and more, and is filled with soft ooze with a huge number of Foraminifera 

 Rhabdammina abyssorum cases. The population of the western trough repre- 

 sents the change-over from Porifera and Brisaster communities to typical 

 central Barents Sea low Arctic communities. The total biomass here is only 

 13-4 g/m 2 . This is explained by a shortage of food {Table 60). 



In the cold waters of the northern part of the trough off the Bear Island 



Table 60 



