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



flow of the Don (in 1921-51 an average of 26-2 km 3 a year; in 1952-55 an 

 average of 19-4 km 3 a year), by a reduction in the biogenic discharge into the 

 Sea (Table 218) and by its transformation in the water reservoir and in the 

 river, as a consequence of which its primary food-value was lowered ; the 

 salinity of the Sea rose by almost 2% , causing a marked reduction in the 

 provision of food for the plankton-eating fish, and as a result their producti- 

 vity became almost 2-5 times lower than the average before the control of the 

 river waters'. 



Among the inhabitants of the Gulf of Taganrog, according to Yablon- 

 skaya's data, there is a series of forms the mass development of which is 

 adapted to a salinity of 4 to 9% (Fig. 235) ; they belong to brackish-water and 

 fresh-water types. Yablonskaya has made a diagram, based on all existing 

 data, of the future distribution of bottom biocoenoses corresponding to a 

 loss of 1 5 and of 40 per cent of the river water (Fig. 236) ; plankton and ben- 

 thos would react differently to a change in the salinity of the Gulf, which would 

 be occupied mainly by brackish-water plankton and Sea of Azov benthos. 



Table 218. A comparison of some indices of the biological conditions of the Sea of 



Azov before and after commencement of control of flow of the river Don 



{E. Yablonskaya) 



Characteristic Average before control 1955 



Phosphorus compounds 2,016 650 



Nitrogen (spring) compounds 179 97 



Nitrogen (summer) compounds 327 58 



Zooplankton biomass 475 40 

 Production of plankton-eating fish (anchovy 



and Clupeonella) in thousands of centners 4,990 1,844 



Peridinean, per cent 88-9 20-3 



Diatoms, per cent 3-9 78-7 



VI. THE SIVASH, OR PUTRID, SEA 



Situation and area 



The Sivash, or Putrid, Sea is a peculiar, large (2,700 km 2 ), subsidiary body 

 of water of the Sea of Azov. Situated to the west of it, the Sivash is connected 

 with it by the shallow (2 to 3 m) and narrow (120 m in width) Tonky Strait. It 

 is separated from the Sea of Azov by the long and narrow Arabat Strelka, 

 and it comprises a complex system of inlets connected by straits and of numer- 

 ous islands. 



The greatest depth of the Sivash hardly reaches 3-2 m in its southern part, 

 while its average depth changes from 0-63 m in its northern part to 0-86 m in 

 the south. With a volume of water of about 1 km 3 the ratio of its volume to its 

 area is equal to 1/1,300, while the corresponding ratio for the Sea of Azov is 

 1/150. 



