THE SEA OF AZOV 499 



(Tubificidae) and Chironomidae, are of importance. 89-3 per cent of the total 

 biomass consists of molluscs, and 8-4 per cent of crustaceans. Marked varia- 

 tions of salinity, and its increase as one moves westwards, cause a decline in 

 the number of species. 



In the most westerly part of the biocoenosis, on coastal sands and shell 

 gravel at depths of 1-5 to 3-5 m and around the Peschanye Islands, lives a 

 very much impoverished (2-6 g/m 2 ) variant of this biocoenosis, with a pre- 

 dominance of the relict polychaete Hypaniola kowalevskyi, the crustacean 

 Corophium volutator and an oligochaete of the Tubificidae family. It is almost 

 free of fresh-water elements and molluscs (mainly Monodacna), and resem- 

 bles somewhat the following ostracode biocoenosis, but without the ostra- 

 codes or Tanypus. Apart from the above-mentioned forms, the presence of 

 the relict crustaceans Pterocuma pectinata and Gmelina ovata and the generally 

 pronounced relict aspect are characteristic of this group. 



The Nereis diversicolor Ostracoda biocoenosis — In the western half of the 

 Gulf of Taganrog, on the soft dark so-called Ostracode muds, lives the Nereis 

 diversicolor Ostracoda biocoenosis, which also produces a number of vari- 

 ants. This biocoenosis penetrates far to the east along the deepest part of the 

 Gulf. In the westward direction the marine forms become gradually dominant 

 in it, although there is still a considerable admixture of Tubificidae and Tany- 

 pus. In the central, deeper part (below 4 m) of the Gulf of Taganrog Ostracoda 

 are markedly predominant in the benthos. With a very low average biomass 

 (9T2 g/m 2 ) the biocoenosis has a strikingly large number of minute crustaceans, 

 whose shells, in innumerable numbers, compose the basis of the sea-bed (the 

 average number of live specimens of Ostracoda is 40,000 specimens per 1 m 2 , 

 at times up to 150,000, at a biomass of 3 to 6 g/m 2 , comprising more than half 

 the total biomass — 58 per cent). 



In the Eisk inlet the Amphipoda Corophium volutator (more than 6,000 

 specimens per 1 m 2 and 26 per cent of the total biomass) produces a large 

 biomass. Colonies of the relict polychaete Hypaniola kowalevskyi are just 

 as abundant here (up to 40,000 specimens per 1 m 2 ). Among the other forms 

 the following should be noted: Nereis diversicolor, Tubificidae, Balanus 

 improvisus, Cardium edule and Monodacna color ata. In general 73-3 per cent 

 of the total biomass consists at times of crustaceans. 



In the western half of the sector occupied by the Nereis-Ostracoda bio- 

 coenosis, at a depth of 4 to 8 m, Nereis diversicolor becomes more and more 

 significant. The biomass here is also low (an average of 23 g/m 2 ) and 40 per 

 cent of it consists of Ostracoda (up to 230,000 specimens per 1 m 2 ). Worms 

 (mainly Nereis diversicolor and Hypaniola kowalevskyi), comprising 47 per 

 cent by weight of the biomass, are almost as significant. Among the other 

 forms the molluscs Syndesmya ovata and Cardium edule and the crustacean 

 Corophium volutator should be noted. 



The Nereis succinea biocoenosis — In the rest of the Sea of Azov, throughout 

 the coastal zone wherever there is a mud bottom, the biocoenosis Nereis suc- 

 cinea is found. The biocoenosis Nereis succinea is met in different biocoenotic 

 combinations, in the main with Ostracoda, Balanus, Cardium, Hydrobia, 

 Pterocuma, Mytilaster, Ampelisca and Corbulomya. 



