624 



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



main sandy silt areas of the Northern Caspian, hitherto practically unin- 

 habited (Fig. 294), were already populated by Nereis. Nereis can endure a 

 scarcity of oxygen and can exist for a long time in its absence (A. Karpevitch, 

 1952). The habitat of Nereis was charted with greater precision during the 

 extensive investigations of the Northern Caspian bottom-living fauna carried 

 out in 1948-49 (Fig. 292). Its total biomass was found to be 1-4 to 1-7 million 

 centners. If we take into consideration the worms consumed by fish and their 



Fig. 294. Distribution of Nereis in Northern and the 



northern part of the Southern Caspian in summer 1 956 



(Romanova, 1960). 



mass mortality after spawning, the annual production of Nereis in the Northern 

 Caspian must be two or three times larger still. 



According to the latest survey, carried out in 1954 and 1956 (V. Osadchikh, 

 1958), the habitat of Nereis and its numbers have remained unchanged in the 

 Northern Caspian. 



The benthos survey of 1956 covered also the Central Caspian and part of 

 the Southern (N. Romanova, 1959); a picture of the quantitative distribution 

 of Nereis obtained showed quantitative indices similar to those for the 

 Northern Caspian (Fig. 294). Thus the total quantity of the Nereis biomass in 

 the Caspian Sea reaches one million tons, while its annual production is two 

 to three times greater. The fate of another immigrant into the Caspian Sea 



