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



animal' Caspian' fauna live in the Azov-Black Sea basin, which comprises 40 

 per cent of the autochthonous Caspian Sea fauna, taking it as 300 to 305 

 species (without the Protozoa). The main part of this fauna comprises the 

 amphipods (33 species), the mysids (8 species), Cumacea (10 species), mol- 

 luscs (11 species) and fish (30 species). 



Only 1 8 representatives of the Caspian fauna five in the open parts of the 

 Black Sea, and in the Sea of Azov as many as 30, mostly fish. 



Yu. Markovsky writes also (1954) that the 'Caspian' forms are the nucleus 

 of the Dnieper-Bug inlet fauna, and he points out the very important fact 

 (1954) that 'the Caspian fauna in the Dnieper-Bug basin has a greater ten- 

 dency towards saline water than the fauna of the Danube-Dniester basin ', i.e. 

 farther west. We have noted a similar phenomenon when comparing the dis- 

 tribution of the Caspian fauna in the Caspian Sea itself and in the Sea of Azov. 

 Consequently, as one moves to the west, beginning with the Caspian Sea, 

 through the Sea of Azov, through the eastern and western parts of the Black 

 Sea and even within the limits of the latter, the Caspian relicts acquire a more 

 and more fresh- water aspect. 'Although a considerable part of the "Caspian" 

 species', writes Markovsky, 'develops best in fresh water . . . many of these 

 forms (about 35 per cent) find the optimum conditions for their development 

 not in fresh but in slightly saline water (1-5 to 3% ) ... a considerable part of 

 the fresh-water "Caspian" forms of the inlet (33-4 per cent) belongs to the 

 fresh-water stenohaline species, which move away when the salinity rises 

 above 1% .' Markovsky relates 59-2 per cent of the species to the forms which 

 can endure a salinity of up to 5% ; only a few species (7-4 per cent) move into 

 water of higher salinity. 



On the other hand, the number of marine forms decreases rapidly at 

 salinities below 3-5 to 4% as one moves farther into the inlet. Markovsky 

 has come to the same conclusion as other workers who have studied the 

 fauna of the Gulf of Taganrog and of the Sea of Azov — that the main 

 habitats of the marine and 'Caspian' forms overlap very rarely and that, in 

 this case, there is little reason to speak of the displacement of Caspian by 

 Mediterranean species. 



In the Dnieper and Don deltas the Caspian fauna comprises on rocky 

 bottoms 80 to 100 per cent, on sands 70 to 86 per cent, on silty-sands 30 to 

 58 per cent, on grey muds 15 to 28 per cent, on black ooze in stagnant bodies 

 of water 1 per cent (F. Mordukhai-Boltovskoy, 1948). This clearly shows the 

 adaptability of this relict fauna to well-aerated rapid currents. Markovsky 

 has identified 78 Caspian forms in the Dnieper inlet, among them two coelen- 

 terates, three polychaetes,* one leech, three gastropods, and six bivalves; 

 the rest are crustaceans. Markovsky has recorded 64 forms in the Bug inlet 

 (Manyunkia caspica should be added to them), among them two coelenterates, 

 four worms, six bivalves, three gastropods and 50 crustaceans. 



In analysing the biocoenoses of the Dnieper-Bug inlet Markovsky dis- 

 tinguished 28 bottom ones, 3 bentho-nectic and 15 plankton ones. The domi- 

 nant forms comprise Dreissensia polymorpha, Monodacna colorata, Clessi- 

 niola variabilis, Cardium edule, Adacna laeviuscula sp.fragilis, Adacna plicata 

 * Manayunkia caspica must be added to them. 



