516 



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



Great changes have thus occurred in the distribution of the bottom- 

 biocoenoses of the Sea of Azov during the last ten years. In 1951 Syndesmya 

 and Hydrobia biocoenoses were being replaced by that of Corbulomya, but 



/ 2 3 * 5 6 



Fig. 243. Distribution of Nereis in the Sea of Azov, g/m 3 (Stark). 1 Not less than 1 ; 

 2 From 1 to 5 ; 3 From 5 to 10 ; 4 From 10 to 25 ; 5 From 25 to 50 ; 6 From 50 to 100. 



even in 1952 the latter was coming to be replaced by the biocoenosis of Car- 

 dium, Mytilaster, Balanus and others. In the southeastern part of the Sea the 

 Syndesmya and polychaete biocoenoses began to appear again in 1955 and 

 1956 owing, possibly, to an increase in the run-off from the land. The bio- 

 mass of the central part of the Sea increases considerably after years of low 

 floods and drops again when there are heavy floods ; the total average benthos 

 biomass also undergoes considerable fluctuations {Table 215). 



