THE CASPIAN SEA 625 



— Syndesmya ovata — is quite different. It was discovered only in 1955 (A. Saen- 

 kova, 1956) and so far its propagation has been limited to individual patches 

 in the southern part of the Northern Caspian. On the average it gave in 1956 

 a biomass of 022 g/m 2 in the area investigated (V. Osadchikh, 1958), and a 

 total of about 200,000 to 300,000 centners. Before 1956 Syndesmya ovata 

 was not recorded in either the Central or the Southern Caspian. There are 

 reasons to believe that the first transplantation of Syndesmya into the Caspian 

 Sea gave no results, while that of 1948 was successful. 



A careful study of the biology of Nereis has shown (G. Belyaev, 1952) that 

 the worms can live in huge numbers (up to 8,900 specimens with a biomass 

 of up to 870 g/m 2 , and with some specimens growing to 14 cm in length and to 

 more than 2 g in weight) in shallow lagoons and inlets of the northwestern 

 part of the Caspian Sea on silty sand soils. The author notes that on these 

 sites Nereis evidently feeds exclusively on soil detritus rich in organic matter. 

 Young and adult worms can easily live through a fall of salinity down to 

 l%o or less; fertilization and egg development require a salinity of not less 

 than 5% . Nereis mass multiplication takes place in shallows in the spring 

 and in greater depths in summer, moreover heteronereis stages are formed 

 which leave the burrows inhabited by immature worms. The worms die after 

 spawning; the whole cycle of their development is accomplished in one year, 

 or perhaps even in one summer. These observations are supplemented by a 

 comprehensive study of the feeding of Nereis (E. Yablonskaya, 1952) which 

 has shown that Nereis, which spends most of its life actually in the soil, 'has 

 developed a capacity for swallowing as food the upper layer of the soil with 

 all its components . . . using, instead of detritus, films at different stages of 

 destruction and plants and animals living in them when they are within 

 reach, without any special selection or hunting for them . . . moreover, the 

 natural conditions of the Nereis environment would make the latter impossible 

 in the majority of cases'. Owing to this manner of feeding, animal remains 

 are very rare in the worms' intestines. V. Beklemishev (1950) has studied in 

 detail the feeding of Nereis pelagica in the Barents Sea. The intestines of this 

 worm are always filled with algae, with a little admixture of animals which 

 were taken in with the algae. N. diversicolor and N. xirens, as well as N. suc- 

 cinea, have adopted the same manner of feeding. The jaws of all these species 

 of Nereis, arranged exactly alike, are not a weapon of attack on living 

 victims, but an instrument for raking algae and detritus into their mouths. 



A. Zhukova (1954) has shown experimentally that Nereis, fed on micro- 

 organisms and yeast, develops and grows normally. She has thus proved the 

 detritus feeding of this worm and confirmed Yablonskaya's data. A survey 

 of the feeding of fish in the Northern Caspian (N. Sokolova, 1952; Ya. 

 Birstein, 1952) has shown that, since Nereis colonies appeared in the Caspian 

 Sea, starred sturgeon has almost exclusively passed over to a Nereis diet, and 

 sturgeon and a number of other fish have added a considerable amount of it 

 to their diet. 



The nutrient qualities of Nereis, both as fat and as protein, and its calorific 

 value are certainly high {Table 266). 

 The calorific value of Northern Caspian benthos has increased greatly with 



2r 



