494 



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



Fig. 236. Diagram of distribution of zooplankton communities (Yablonskaya, 1957) : 

 A At an average river discharge ; В At 15% of the river discharge ; С At 40% only 

 of river discharge; 1 Fresh-water community; 2 Brackish-water community; 

 3 Sea of Azov community ; 4 Black Sea community. 



Benthos 



Micro-organisms. Data on the bacterial population of the Sea of Azov were 

 also obtained by Knipovitch's expedition. Apart from the above-mentioned 

 micro-organisms, which give off hydrogen sulphide during the conversion 

 of sulphates into carbonates and produce this gas during the process of decom- 

 position of organic compounds, micro-organisms which oxidize hydrogen 

 sulphide, those which nitrify and denitrify, iron-depositing micro-organisms, 

 chitin-decomposing and other micro-organisms have been recorded in the 

 composition of the Sea of Azov micro-flora. B. Isatchenko (1924) carried out 

 a quantitative survey of the Sea of Azov bottom micro-organisms and obtained 

 for some coastal areas the sum of 274 to 776 million specimens per gramme 

 of the soil. If the average size of micro-organisms is 1 /x 3 , and their average 

 number 500 millions, than 1 g of the soil contains an approximate weight of 

 0-5 mg of micro-organisms. This, when converted to 1 m 2 , would give a huge 

 quantity for the mass of micro-organisms and gives some idea of the colossal 

 processes taking place in the sea-bed, especially if we keep in mind that the 

 annual production of micro-organisms in the Sea of Azov is hundreds and 

 maybe thousands of times greater than its biomass. 



Only within the area of the Kerch Strait itself is the quantity of micro- 

 organisms greatly reduced. 



