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



Table 266. Nutrient value of Caspian invertebrates (E. Bokova, 1946; L. Vinogradov, 

 1948; M. Zheltenkova, 1939) 



its colonization by Nereis, and in 1946-49 21 to 30 per cent of its total calorific 

 value was due to Nereis. 



Changes in benthos distribution (quantitative and qualitative) in the Cas- 

 pian Sea are controlled not only by the distribution of new immigrants, but 

 also by its rise in salinity, especially in the Northern Caspian. 



Mytilaster, Cardium and Nereis have moved far northwards ; on the other 

 hand Dreissena polymorpha and Didacna trigonoides, much less tolerant of 

 salinity, have receded to the northwest and reduced the area of their habitat. 



Zoobenthos biomass of the Caspian Sea. The following is a count of the 

 benthos biomass in the different areas of the Caspian Sea : 



Southern 116,227 tons 



Central 10,000,000 tons 



Northern 6,100,000 tons 



Total 27,622,700 tons 



Thus almost four-fifths of all bottom fauna are concentrated in the Central 

 Caspian. Plankton does not form such accumulations there, especially along 

 the eastern shores ; the cause of the abundance of benthos is as yet unknown. 



Food value of zoobenthos of Caspian Sea. Data on the qualities as food of 

 the main species of the Caspian and Azov-Black Sea fauna are of interest. 

 E. Bokova (1946) gives some interesting information on this aspect in her 

 work {Tables 267, 268, 269). It is evident from these data that species of the 

 genus Adacna have the highest food value among the Caspian molluscs. 

 Mytilaster and Syndesmya are close to them in their properties {Table 267). 



The molluscs occupy first place in the Caspian benthos and in the diet of 

 Caspian fish. 



Crustaceans are different in their nutrient qualities and it is evident from 

 Table 267 that crustaceans, which occupy second place in the diet of Caspian 

 fish, are much superior to the molluscs in their significance as food. 



The average percentage of protein and fat content in crustaceans is more 

 than five times higher than that in molluscs, while the ash content is corres- 

 pondingly three times lower. 



