THE SEA OF AZOV 497 



Table 204 



Mean number Mean 



Group of percentage biomass percentage 



specimens/ 1 m 2 g/m 2 



Total 15,166 100-0 1320 100-0 



For its salinity the Sea of Azov should be included, according to Re- 

 mane's (1935) classification, in the mesohaline zone. The true relict brackish- 

 water fauna is concentrated in the inner part of the Gulf of Taganrog, living 

 there at a salinity below 3-6% . 



Zoobenthos biocoenoses. Bottom biocoenoses of the Sea of Azov, which were 

 comprehensively investigated by V. P. Vorobieff (1944), F. Mordukhai- 

 Boltovskoy (1939), and later by I. Stark (1951, 1955, 1958), can be divided 

 first of all into two large groups : 



(1) Relict biocoenoses, with early Pontic relicts as dominant species — 

 Dreissena, Monodacna, Hypaniola and some species of Corophium and 

 Pontagammarus. 



(2) Mediterranean or Azov-Black Sea biocoenoses, with Ostracoda as domi- 

 nant species as well as Corophium, Cardium, Syndesmya, Mytilaster, 

 Corbulomya, Hydrobia, Balanus, Nereis, Sphaeroma and Pectinaria. 



However, both these groups, especially the first, are distinguished by a 

 strongly marked oligohalinity ; this, and the small difference in their living 

 conditions, leads to a great similarity in the type of biocoenosis, making easy 

 the transition of various combinations into each other. 



The general picture of the autumn distribution of bottom biocoenoses and 

 of the biomass for 1934-35 is given in Fig. 238a, b. Let us consider the brief 

 characterization of individual biocoenoses marked on the chart, beginning 

 from the east. 



Biocoenosis: Dreissena-Monodacna-Unionidae — In the most eastern corner 

 of the Gulf of Taganrog, in front of the Don delta on the estuarial shallows, 

 there are situated different variations of the Dreissena-Monodacna-Unionidae 

 biocoenosis. Nearer to the Don, in the least saline part, Dreissena is predomi- 

 nant. Only the most hardy forms can endure sharp fluctuations of salinity 

 and sometimes considerable drying-up caused by land winds. The mean bio- 

 mass here is 13 g/m 2 , of which Dreissena polymorpha forms 1 1 -6 g/m 2 . Among 

 the other forms the relict crustaceans Cumacea (Pterocuma sowinskyi, Steno- 

 cuma tenuicauda, species of the Schizorhynchus genus), Mysidacea (Metamy- 

 sis strauchi, Mesomysis kowalewskyi), Amphipoda {Corophium curvispinum, 

 Pontogammarus abbreviatus), the species of Gmelina genus, Oligochaeta 



2i 



