THE CASPIAN SEA 575 



(T. Nebolsina, 1959). The original home of both forms is on the northeastern 

 shores of North America. The medusa has apparently come to the Sea of Azov 

 directly, while the crab arrived in the Black Sea via Dutch coastal waters 

 (Zuyder Zee). This latter brackish-water form had originally immigrated from 

 North America and was described in the Zuyder Zee as a new form, Hetero- 

 panope tridentata. Rh. harrisii found favourable conditions for its existence in 

 the Sea of Azov and the Don estuary ; in its further travel it proceeded by 

 canal into the Caspian Sea where it found a fourth home. 



A. Karpevitch (1958) and E. Bokova (1958) have raised the problem of the 

 utilization of Caspian crustaceans as an acclimatization stock for the Aral 

 and Baltic Seas and for Lake Balkhash. The ecology and physiology of a 

 number of mass forms of Caspian crustaceans were carefully studied and the 

 following were recommended for the Aral Sea and Lake Balkhash : Meso- 

 mysis (Paramysis) kowalewskyi, M. baeri and M. intermedia (Karpevitch), 

 and for the Aral and Baltic Seas Schizorhynchus bilamellatus, Pterocuma pecti- 

 nata of the Cumacea, and Corophium nobile and C. curvispinum of the Amphi- 

 poda (Bokova). The three mysids were transported in the adult stage into the 

 Aral Sea in the summer of 1958. The results of this attempt at acclimatization 

 are so far unknown. 



Bogachev was the first to record in 1928 the mollusc Mytilaster lineatus 

 in the Caspian Sea ; he thinks that it was brought from the Black Sea during 

 the civil war from Batum on small craft, the undersides of which are often 

 covered with clumps of Mytilaster. Closing its valves tightly the mollusc 

 can endure life in the air for a long time. 



The history of the colonization of the Caspian Sea by this mollusc Myti- 

 laster and of the annual increase of its biomass was studied by V. Brotzky and 

 M. Netzengevitch (1940). As early as 1932, according to their data, Mytilaster 

 had already moved from the Baku area, following the main currents, along the 

 coast of the Southern Caspian, colonized the eastern shore of the Central 

 Caspian and penetrated into the southern part of the Northern Caspian. 

 In the following years it moved still father north and along the western coast 

 of the Central Caspian (Figs. 272 and 273) ; its biomass was growing rapidly. 

 In 1938 Mytilaster biomass in the Caspian constituted five million tons, and 

 if we include the growths on the cliffs this quantity will be at least doubled. 



Besides actual growth of the Mytilaster biomass the increase of its relative 

 significance in the total biomass has also been observed. Thus, for example, in 

 1933 on the eastern shore of the Southern Caspian Mytilaster composed only 

 18 per cent of the total benthos biomass ; by 1935 it composed as much as 89 

 per cent, and in the following years more than 90 per cent. Moreover, it over- 

 whelmed the growth of other benthos components, as may be seen by com- 

 paring data for the western coast of the Southern Caspian {Table 239). 



It is difficult to decide at the moment whether Mytilaster acclimatization in 

 the Caspian Sea is favourable or unfavourable for its fisheries. On the one 

 hand Mytilaster no doubt suppresses the development of some valuable food 

 forms, in particular Dreissensia ; on the other, it now forms part of the diet 

 of many commercial fish. In the Southern and to some extent also in the Central 

 Caspian sturgeon feed on this mollusc to a considerable extent; starred 



