THE BERING SEA 



831 



feebly developed (M. Vinogradov, 1956). The Copepoda are concentrated in 

 the lower horizons (Fig. 422). 



As in the Sea of Okhotsk, but to a lesser extent, the cold intermediate layer 

 influences the vertical migration of zooplankton, dividing it into three groups : 

 those migrating above the cold layer {Calanus tonsus, С cristatus, Eucalanus 



Cape ChuKolsK 



Fig. 421 . Distribution of zooplankton biomass (mg/m 2 ) on cross section through the 

 Bering Sea, spring 1952). A Total zooplankton biomass; В Eucalanus bungii bio- 

 mass; С Calanus tonsus biomass; D C. cristatus biomass (Vinogradov). 



bungii), forms migrating through it {Metridia pacifica, Pleuromamma scutu- 

 lata, Candacia columbiae and others), and those for which in their migrations 

 the cold layer serves as a 'ceiling'. When the boundaries of the cold inter- 

 mediate layer become less definite in summer the migration system becomes 

 complete. Calanus cristatus, and C. tonsus and later the cold-water Eucalanus 

 bungii sink down in autumn when the surface layer gets colder. 



M. Vinogradov (1956) notes a characteristic peculiarity in the vertical 



