424 



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



August 1948 



1949 Aug Sept.1950 Aug. 1951 

 Western half 



Sept 1948 



1949 Aug Sept 1950 Aug. 1951 

 Eastern half 



Fig. 204. Annual fluctuations in the volume of river-discharge and in the biomass of 

 nutrient zooplankton in the to 25 m layer of the Black Sea. 1 Total discharge ; 2 

 Summer floods; 3 Nutrient zooplankton biomass; 4 Penilia avirostris biomass 



(Kusmorskaya). 



different. Thus in 1955 a sharp decrease of food zooplankton and a mass 

 development of the diatoms Rhizosolenia calcar-avis were observed. They 

 may be the link in an inverse relationship. The same picture was observed in 

 the Sea of Azov in the summer of 1955 (25 to 50 mg/m 3 in July and August). 

 A considerable mass of fish, chiefly anchovy, moved away from the north- 

 western part of the Sea. The feeding conditions began to deteriorate in the 

 northwestern part of the Black Sea after 1952. In 1954 the amount of food- 

 plankton decreased by several times (E. Yablonskaya, 1957). In 1955 the 



Table 170. Annual and seasonal fluctuations in the biomass of food zooplankton 

 in different parts of the Black Sea {A. Kusmorskaya, 1954) 



