THE SEA OF JAPAN 



761 



They are particularly abundant in the to 50 m layer in January and February 

 (L. Ponomareva, 1955) when their biomass is between 1 and 3 mg/m 3 in large 

 areas of the Sea. Euphausiids feed on calanoids with an admixture of various 

 plankton. They are probably the greatest consumers of calanoids. 



As a result of some alterations in the Kuroshio system a certain fall of 

 temperature was observed in 1939 in the Sea of Japan, which increased in 

 subsequent years. Sardine fisheries decreased markedly in 1941, and in 



< WO mg 



100-200 mg 



200-500 mg 



500- WOO mg 



northern boundary 

 of the zone of bloom 



Fig. 375. Distribution of zooplankton biomass (mg/m 3 ) in northwestern 

 part of Sea of Japan between 50 and 200 m, summer 1 952 (Meshcherya- 



kova, 1950). 



1942 sardines did not enter the Sea of Japan. They were not caught off the 

 Soviet shores of the Sea of Japan for many years after this. 



This fall of temperature necessarily affected the plankton, and in May 1941 

 phytoplankton was still predominant in the northwestern part of the Sea 

 (A. Kusmorskaya, 1950) — mainly the diatoms Coscinodiscus oculis iridis. 

 In the eastern part of the region species of the genus Chaetoceros were domi- 

 nant, and in the southern Thalassiothrix longissima. Calanus finmarchicus, 

 Pseudocalanus elongatus, Oithona similis, Metridia lucens and other cold-water 

 forms were among the most widely distributed zooplankton components in 

 the spring. The mean biomass of zooplankton in May was only 136 mg/m 3 



