THE BARENTS SEA 



143 



communities reach the edge of their habitat; they are absent from the 

 eastern and northern parts of the Barents Sea. 



In the biocoenosis Modiola modiolus-Pecten islandicus, the polychaetes 

 Thelepus cincinnatus, the Ophuroidea Ophiopholis aculeata, Balanus balanus, 

 the sea-urchin Strongylocentrotus droebachiensis and some Bryozoa are the 



Fig. 56. Composition of main bottom bio- 

 coenoses of Barents Sea (Brotzkaya, Zenke- 

 vitch and Filatova). / Porifera; II Central; 

 III Eastern (medium depths) ; IV Eastern lit- 

 toral ; V Northern littoral ; VI Northern (deep 

 water) ; VII Waldheimia-Brisaster. I Lamelli- 

 branchiata ; 2 Gephyrea ; 3 Crustacea ; 4 Coe- 

 lenterata; 5 Polychaeta; 6 Echinodermata ; 

 7 Porifera; 8 Sipunculoidea; 9 Gastropoda; 10 

 Tunicata ; 11 Brachiopoda ; 12 Varia. Average 

 biomass is given in numerals (g/m 2 ). 



most important. This biocoenosis is distributed mainly over large-grain sand 

 and shale gravel, in zones of the constant ebb and flow of tidal streams. 



V. Zatzepin and Z. Filatova (1945) have noted that in summer these com- 

 munities keep to waters of 6° to 10° and in winter to 0-5° to 2-5°; large 

 growths of macrophy tes are frequently met, among them the branched Litho- 

 thamnion (red algae). On the Murman coast the biomass of Modiola bio- 

 coenosis reached 1 to 1-5 kg/m 2 (an average of 350 g/m 2 ). Proceeding west- 

 ward and southward the biocoenosis changes its qualitative composition — 

 its cold-water forms such as the molluscs Saxicava arctica, Pecten islandicus 



