812 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



ture waters of the Amur Inlet with the cold waters of the northern Sea of 

 Okhotsk current and the warmer waters entering from the southeast. The ben- 

 thos biomass is generally high (100 to 500 g/m 2 ). The distribution of the main 

 biocoenoses is determined also by the nature of the bottom soils. There is a 

 belt of fine-grain, more or less silty sand round the whole area. Soft soils ex- 

 tend from the southeast to the northwest following the bottom topography. 



Fig. 407. Distribution of biocoenoses of north- 

 western part of Sea of Okhotsk (Pasternak, 1957). 



1 Area of predominance of fixed fouling fauna ; 



2 Area of predominance of Echinarachnius par ma ; 



3 Area of predominance of large detritus-eating 

 bivalves ; 4 Ophiura sarsi predominance ; 5 Bio- 

 coenoses with predominance of filter-feeders; 

 6 Amphipod predominance ; 7 Predominance of 

 forms swallowing detritus with the soil ; 8 Area 

 of predominance of small bivalves. 



Zones of the predominance of fouling fauna in the northeastern part of the 

 region investigated could be singled out among the biocoenoses of the region 

 (Fig. 407). In the deeper parts of the trench and on its eastern slopes grass 

 Porifera with an admixture of Hydroidea are predominant — Cladocarpus, 

 Sertularia, Bonnevillea, Abiettinaria ; the Bryozoa, Smittina and Membrani- 

 pora ; Sabellidae and Actinia like Chondractinia, Ophiopholis aculeata, Coro- 

 phiidae and others. 



Large spaces of this region are occupied by forms which collect detritus 

 from the surface of the bed. Hard fine-sand beaches are inhabited by large 



