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



But Y. Sorokin, criticizing Kriss' method of water sampling, has recently 

 argued against the supposedly huge productivity of autotrophic sulphur bac- 

 teria and protein origin of hydrogen sulphide. In his opinion nitrificators and 

 denitrificators, practically absent from the Black Sea depths, play only a minor 

 role, and autotrophic production does not exceed that of photosynthetic 

 activity. 



Quantitative distribution of phytoplankton. P. Usatchev (1926, 1928) laid the 

 foundation of the quantitative study of the Black Sea phytoplankton in his 

 survey of the northwestern part of the Sea. Later some data were collected 

 by N. Morozova-Wodjanitzkaja for the shores of the Crimea (1940), by 

 G. Konoplev (1937-38) for the Bay of Odessa, by V. Nikitin (1939) for the 

 Batum area and by S. Maljatzky (1940) for the open part of the Sea. 



The diatoms are of preponderant significance in the Black Sea phyto- 

 plankton, the second place is occupied by Dinoflagellata. The number of plant 

 specimens in the plankton is exceeded by that of the animals (Fig. 198a, b). 

 As in the open seas there are in the Black Sea two main bloom periods : the 

 autumn-winter-spring one linked mainly with a mass development of dia- 

 toms, and a much weaker summer one, controlled by the multiplication of 

 Dinoflagellata. An increase of the diatoms is again observed in the autumn 

 (Fig. 199). In the winter there is a sharp preponderance in the phytoplankton 

 of Skeletonema costatum (up to 4 million cells per litre), Chaetoceros radians 

 and Ch. socialis (up to 31 million cells), Thalassionema nitzschioides and 

 Thalassiosira nana (up to 30,000 specimens) and Cerataulina bergoni (up to 

 1-7 million specimens). 



From May onwards, and especially in the hot months (July and August), 

 the development of Dinoflagellata proceeds vigorously : Exuviella cordata (up 

 to 18,000 per litre), Prorocentrum micans (up to 72,000 specimens), Goniaulax 

 polyedra (up to 66,000 specimens), some species of Glenodinium apiculata 

 (up to 39,000 specimens) and Peridinium triquetrum (up to 43,000 specimens). 

 Among the diatoms Thalassionema nitzschioides also grows in large numbers in 

 the summer. A second autumn maximum of diatoms is observed in November, 

 when the phytoplankton passes into its winter state {Table 164). 



The spring outburst of phytoplankton is four or five times greater in its 

 number of cells than the winter maximum and 2,000 times greater than the 

 autumn maximum. A comprehensive picture of the quantitative sequence of 

 phytoplankton during the year in the circumlittoral parts of the Bay of 

 Sevastopol is given in Table 165 (according to Morozova-Wodjanitzkaja's 

 data in the year 1938-39). 



Marked changes, not only seasonal but annual, are observed in the com- 

 position and quantity of phytoplankton in the Black Sea. The average annual 

 number of Dinoflagellata in the plankton of the Bay of Sevastopol was 

 31,000 specimens in 1938, and of diatoms 19,000 specimens per litre, with an 

 average annual total amount of phytoplankton 52,000 cells per litre ; while 

 in 1939 the corresponding data were: 14,000, 3,240,000 and 3,257,000 per 

 litre. Thus the average annual number of Dinoflagellata in 1939 was half that 

 in 1938, while the number of diatoms in 1939 was, on the contrary, so much 



