THE CASPIAN SEA 



623 



in the Southern). In the Central Caspian the higher crustaceans, Gammari- 

 dae and Corophiidae, which penetrate to great depths and give a biomass of 

 about 6 g/m 2 , develop in considerable numbers. The Nereis biomass reaches 

 0-6 to 0-8 g/m 2 , based on the whole Sea area, and 3-5 to 5-0 g/m 2 for the areas 

 no deeper than 200 m. Its favourite habitats are Mytilaster concretions, 

 where it apparently uses the mollusc faeces and pseudofaeces rich in organic 

 matter. 'The vigorous development and the wide eurybiotic capacity of the 

 members of Mediterranean fauna which have penetrated into the Caspian 

 Sea have often been recorded', writes N. Romanova (1959). 'The consider- 

 able adaptability of the immigrants, their higher viability than that of the local 

 autochthonous fauna, is illustrated by the composition of the Southern 

 Caspian fauna. Exceptionally high biomass is always due to the development 

 of species of Mediterranean fauna : Mytilaster, Cardium and Nereis ', with this 

 difference between Mytilaster and Nereis, that the first crowds out other bi- 

 valves in its development, while the second does not crowd anything out 

 when growing in large numbers. 



A detailed survey of Nereis colonies, of their utilization by fish and of the 

 change in the composition of the bottom biocoenosis, was again organized 

 in 1948 and 1949; a series of experimental researches was also carried out. 

 The results of this work were published in a special volume (1952). 



Special attention was naturally paid to Nereis and Syndesmya in their new 

 habitat. As has been mentioned above, the worm was discovered in the Cas- 

 pian Sea in 1944, i.e. five years after its transplantation. By that time the 



Table 265. Benthos composition of Central and Southern Caspian 



