704 



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



42° N latitude and react on each other. The boundaries of these zones agree 

 closely with the distribution of certain mass forms of plankton (Fig. 338). 

 To the north of the zone of mixing of the waters plankton is typically boreal, 

 with a predominance of Calanus cristatus, C. plumchrus, Eucalanus bungii 

 bungii and Metridia ochotensis (K. Beklimishev and V. Burkov, 1953). To 

 the south of it Velella and Janthina become predominant, while large masses 



Fig. 338. Distribution of zooplankton communities in 

 the surface waters of the northwestern Pacific in August 

 to October 1954. 1 Boreal complex; 2 Zone of mixing; 

 3 Tropical complex. Dashed line is an 18° isotherm on 

 the surface of the water (Bogorov and Vinogradov, 1955). 



of Doliolum and Salpae, Lepas, Physalia, Porpita, Cestus and others make 

 their appearance. 



This type of replacement of the population of certain waters is clearly seen 

 in the phytoplankton too (G. Semina, 1958) (Fig. 339). Bogorov has given an 

 exceptionally clear and complete picture of the distribution of zooplankton 

 within the zone of the meeting of the Kuroshio and Oyashio currents (the 

 Polar front). North of latitude 40° to 42° surface waters have a winter tem- 

 perature below 3° and a summer temperature of up to 14° or 15°. South of this 

 zone of sub-Arctic convergence (the Polar front) the temperature rises to 

 26° to 28° in summer, while in winter it is 18° to 20°. The convergence zone is 

 100 miles wide in summer and several times wider in winter. To the north of 

 it the boreal plants {Thalassiosire nordenskjoldii, Chaetoceras convolutus, Ch. 

 atlanticus, Ceratium longipes) and the animals {Calanus plumchrus, Eucalanus 

 bungii, Calanus cristatus, Sagitta elegans, Euphausia pacifica, Thysanoessa 



