788 



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



Kuril Islands are formed by younger Mesozoic tectonic structures. Kam- 

 chatka and the Kurils are built of volcanic rock. Shelekhov Bay, especially in 

 its inner part, has very high tides (reaching 13 m), very strong tidal currents 

 and wide rock and sand beaches, and more rarely shores which dry out at low 

 tide. A series of broad lagoons, formed by alluvium from the rivers, stretches 

 along the northern shore of Sakhalin. The whole western shore of Kamchatka 

 is an alluvial plain. 



The climate of the Sea of Okhotsk is more severe than that of any other 

 Far Eastern Sea. Its characteristics have been given above. Its cold inter- 

 mediate layer — a similar one is known only in the Kara Sea — is exceptionally 

 wide, especially in the north of the Sea. 



The characteristic features of the distribution of temperature, salinity and 

 oxygen are given in Table 314. 



Table 314 



The presence throughout the year of a substantial intermediate cold layer 

 in the Sea of Okhotsk has a decisive effect on the distribution of the zoo- 

 plankton and its vertical migration, since it cuts off the layers of water lying 

 above and below it. The benthos distribution is considerably affected by the 

 low content of oxygen in the depths of the central and southern trenches 

 (Fig. 393). The thick ice cover which forms in winter has an immense in- 

 fluence on the development of life in the coastal zone. 



II. FLORA AND FAUNA 



Micro-organisms 



Fairly high indices are obtained for the quantitative distribution of micro- 

 organisms in the region of the Kuril Islands {Table 315). 



Similar data were obtained later by A. Kriss (1958), who also gives the 

 mean biomass of micro-organisms for the Kuril-Kamchatka trench. It is 

 evident from the data of the two columns in Table 315 that the number of 



