THE SEA OF JAPAN 



759 



considerably richer again (Fig. 377). The layer of decreased biomass coincides 

 with the layer of sudden change. It is of interest to note that the diurnal 



Fig. 373. Distribution of main species of Copepoda in Sea of 

 Japan (Khun and Meshcheryakova, 1954). 



vertical migrations of most of the main zooplankton species in the Sea are 

 only feebly developed. 



The euphausiids, which at times display a mass development, form a very 

 important group of zooplankton. Members of four species of this group — 

 Thysanoessa longipes, Th. inermis, Th. raschii and Euphausia pacifica — are 

 found in the Sea of Japan. The euphausiids form the main food of many com- 

 mercial fish (herring, mackerel, alaska-pollack, pink salmon) and of whales. 



