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



July, Tintinnoidea forms 16-8 per cent of the total zooplankton. At times, 

 when the number of its specimens reaches 50 million per 1 m 3 , they yield a 

 biomass of more than 1 g/m 3 . In the Gulf of Taganrog the quantity of ciliates 

 is much smaller. Rotifera are also important in the Sea of Azov zooplankton,' 

 especially in the Gulf of Taganrog ; their annual biomass is about 25 per cent 

 of the total zooplankton, and in the spring even 80 or 90 per cent. Asplanchna 

 priodonta, Brachionus quadridentatus, B. plicatiles, Synchaeta baltica, S. 

 у or ax and Pedal ion oxyuris are the principal forms. There is a considerable 

 admixture of typical fresh-water forms, such as Keratella cochlearis, K. 

 quadrata, Triarthra longiseta and others, in the eastern part of the Gulf of 

 Taganrog. Mollusc larvae are found in the plankton of the Sea of Azov 

 almost all the year round, but they yield a considerable development in the 

 summer. In June they produce 94 mg/m 3 (14-5 per cent of the total zooplankton 

 biomass). Finally, the Mysidacea, which rise from the bottom during the 

 hours of darkness, play a considerable part in the plankton. The main forms 

 here are Macropsis slabbed, Mesomysis helleri and also M. kowalewskyi in the 

 Gulf of Taganrog. The first of these forms produces at night in the Sea of 

 Azov 152 mg beneath 1 m 2 of surface area, and in the Gulf of Taganrog even 

 185 mg; Mesomysis kowalewskyi in the Gulf of Taganrog produces 254 mg, 

 and M. helled in the Sea of Azov, 57 mg. A small part of the Sea of Azov 

 zooplankton consists of Cladocera (Evadne tdgona and Podon polyphemoides) 

 and polychaete larvae. G. Pitzik (1951) gave an interesting comparison of the 

 mass development of phyto- and zooplankton in the Sea of Azov and of the 

 significance of the first as food for the second : ' Early in the spring phyto- 

 plankton develops in such colossal quantities, that the scarce zooplankton 

 leaves much of it untouched. At that period for every gramme of zooplankton 

 there is 30 to 70 g of phytoplankton, including 27 to 66 g of diatoms and 2 to 

 4 g of peridineans. With such a ratio the main mass of phytoplankton, 

 dying off, is deposited on the sea-bottom ; together with the detritus which is 

 brought down in huge amounts by run-off from the land, it forms large de- 

 posits of organic matter. In late spring there are only 0-9 to 1-2 g of phyto- 

 plankton per 1 g of zooplankton . . . and the feeding conditions for zoo- 

 plankton, and through it for plankton-eating fish as well, may become un- 

 favourable. ... In the summer and at the beginning of autumn ... in the Sea 

 of Azov itself, there are 2 to 1 1 g of phytoplankton, among it 1 to 8 g of peri- 

 dineans per 1 g of zooplankton. ... In the Gulf of Taganrog during the warm 

 season . . . there are generally 2-5 to 7 g per 1 g of zooplankton ... the main 

 part of it consisting of blue-green algae. . . . ' The same relationship is retained 

 in winter in the Sea of Azov itself. 'Thus in the course of the year the most 

 favourable feeding conditions for zooplankton . . . are found in the summer 

 and at the beginning of the autumn, when the peridineans are preponderant 

 in the Sea of Azov itself . . . and the blue-green and green algae and flagellates 

 ... in the Gulf of Taganrog.' 



Reduction of the discharge of the river Don in 1950, caused by the regula- 

 tion of its flow, led to the salt-water fauna moving deeper up into the Gulf of 

 Taganrog and the fresh- water fauna receding. In 1951 the discharge of the 

 Don was considerably greater, and the Gulf fauna moved in the opposite 



