706 



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



viridis as cold-water forms, and Planktoniella sol and Vultar sumatranum 

 as warm-water forms, may serve as good indicators of the warm (Kuroshio) 

 and cold (Oyashio) waters of the northwestern part of the Pacific Ocean 

 (G. Semina, 1958). Alterations in the plankton density (Fig 340) and in the 

 indices of its primary production (Fig. 341) are just as characteristic. Off the 

 Kamchatka coast primary production in the autumn of 1955 was 20 times 

 higher than in the tropical region. Plankton biomass in the waters adjacent to 

 the Kuril Islands is on the average 200 mg/m 3 in autumn. Increasing gradually 

 to the southeast, it becomes more than 500 mg/m 3 within the region of greatest 



140' 



145 



160 



165° 



Fig. 340. Distribution of zooplankton biomass in 

 to 100 m layer of the northwestern Pacific, August to 

 October 1954. 1 Above 500 mg/m 3 ; 2 From 250 to 

 500 mg/m 3 ; 3 From 100 to 250 mg/m 3 ; 4 Below 100 

 mg/m 3 (Bogorov and Vinogradov). 



vertical mixing (V. Bogorov and L. Vinogradov, 1955), reaching at times 

 2,000 to 3,000 mg/m 3 . Still farther to the southeast the plankton biomass falls 

 to 50 or even 20 mg/m 3 . However, it has to be taken into account that in the 

 warm tropical waters the number of plankton generations is considerably 

 higher and the period of multiplication much longer, thus compensating for 

 the small indices of isochronous biomass. In the Kuril-Kamchatka region, 

 for instance, Calanus plwnchrus has only two multiplication maxima, the 

 spring and autumn ones, and only two seasonal generations. The dominant 

 forms of the surface euphotic zone (0 to 200 m) in Kuril (boreal) waters have 

 been given above. 



In May and June 1953 the to 200 m layer contained 31-2 per cent of the 

 total zooplankton biomass of the whole huge water column of the Kuril- 

 Kamchatka trench. The transition zone immediately below it contained 



