THE SEA OF AZOV 487 



A. Okul and G. Pitzik, relate to 1937 and 1950; the picture may have been 

 different in other years. In particular P. Usachev (1927) notes that the blue- 

 green algae play an important part in the life of the Sea of Azov. This con- 

 tradiction may be explained by the erroneous picture obtained by the qualita- 

 tive method of investigation, since the blue-green algae accumulate mainly on 

 the surface of the sea. Apart from the spring, a mass development of the 

 Sea of Azov plankton is also observed in the summer and autumn up to 

 October. This course of plankton development, in the opinion of N. M. Kni- 

 povitch (1932), indicates that there is no shortage of nutrient salts in the water 

 of the Sea of Azov ; this is apparently due to the proximity of the bottom, 

 the rapidity of the processes of mineralization and regeneration, and generally 

 to a large amount of limiting nutrient salts. 



The frequently observed saturation of the Azov Sea water with oxygen is 

 the result of a similar huge accumulation of algae in the water-column. A 

 case was mentioned above of the Sea of Azov phytoplankton reaching a 

 density of 300 to 400 g/m 3 , which approximately corresponds to the same 

 amount of grammes by weight. If the depth of that station was 8 m, up to 

 2 or 3 kg of phytoplankton alone could have been concentrated in a water- 

 column of 1 m 2 cross section. Moreover, the plankton is often very unevenly 

 distributed — in patches and strips, carried about by currents and vertical 

 movements of the water. A particularly important development of plankton 

 can be observed in the western part of the Sea, sometimes in the middle part 

 of the Gulf of Taganrog. 



Qualitative composition ofzooplankton. The qualitative composition of the Sea 

 of Azov zooplankton (G. Pitzik and A. Novoshilova, 1951) can be expressed 

 in the form of Table 199. 



Table 199 



Protozoa 14 species Copepoda 31 species 



Coelenterata 6 species Mysidacea 1 1 species 



Rotatoria 20 species Cumacea 6 species 



Chaetognatha 1 species Amphipoda 2 species 



Cladocera 17 species 



Total 108 species 



In addition the plankton usually contains a large number of the larvae 

 stages of polychaetes, brozoans, Cirripedia and decapod crustaceans which 

 live on the bottom. However, only 50 species in all are found in the main 

 basin of the Sea of Azov, and only a few of these develop in large masses. 

 Among the separate groups, divided according to their origin, those most 

 characteristic of the Sea of Azov are the following : 



I. Novo-Euxine relicts (mainly in the Gulf of Taganrog) Evadne trigona, 

 Cercopagis pengoi, Heterocope caspia, Calanipeda aquae dulcis and 

 others. 



