THE SEA OF OKHOTSK 



793 



Table 316. Vertical distribution of phytoplankton biomass and 



temperature ranges in central part of Sea of Okhotsk during 



the spring bloom 



The vertical distribution of Okhotsk plankton is greatly affected by the 

 presence of the cold intermediate layer. Plankton biomass decreases markedly 

 at depths of 40 to 50 m {Table 316), increasing again below the cold layer (at 

 100 to 150 m). This is clearly seen from specimens collected from the central 

 part of the Sea during the spring bloom (Fig. 395) (M. Vinogradov, 1954). 



This vertical distribution of plankton is consistent with the changes of 

 temperature. The sinking of phytoplankton and the vertical migration of zoo- 

 plankton is restricted by the high range of temperature and density in the 

 upper and lower limits of the cold intermediate layer. Oithona similis and 

 Pseudocalanus elongatus are adapted to the surface zone (M. Vinogradov, 

 1954). Zooplankton organisms, which are capable of diurnal and seasonal 

 vertical migrations into the upper layer of the Sea, characterize the transi- 

 tional cold zone. They are composed mainly o\ Calanus tonsus (C.plumchrus), 

 С finmarchicus and C. cristatus, Eucalanus bungii, Metridia okhotensis and, 

 to a lesser extent, M. pacifica and Oncea borealis. The number of species in 

 the deep layers is much higher, and some of them do not penetrate at all into 

 the upper two horizons. These forms may be divided into two groups, those 

 which migrate, and those which do not. The first group includes species living 



BIOMASS, g/m 3 



в to го зо 



BIOMASS, g/m 3 

 0,5 1,0 (5 



m 



wo 



гоо 



a /ooo 



гооо 



Fig. 395. Vertical distribution of zooplankton 



biomass (g/m 2 ) in Sea of Okhotsk (left) and 



Bering Sea (right) (Vinogradov). 



