THE SEA OF AZOV 479 



The second important factor leading to high productivity of the Sea of 

 Azov is the summer warming both of the whole water-column and of the sea- 

 bottom for a long period from April to October. The heating of the upper 

 layer of water of the Sea of Azov corresponds to approximately 3,800 degree- 

 days annually, and that of the bottom-layer to a little less. 



The intensity of the productive processes of the Sea of Azov may possibly 

 be connected in some measure with the ice-formation process, or, more pre- 

 cisely, with the melting of ice. If this phenomenon has a wide impact in nature 

 then, given that the shallow depths of the Sea, and the fact that its ice-cover 

 composes one twentieth to one twenty-fifth of the whole volume of water, 

 the effect of melted water on the development of life in spring must be 

 particularly important. 



Composition and heterogeneity of population 



At present 226 species of invertebrates (Mordukhai-Boltovskoy, 1960) and 79 

 forms of fish have been shown to exist in the Sea of Azov. The list includes 

 among the invertebrates 35 species of polychaetes, 33 species of molluscs, 

 30 species of lower and 61 species of higher crustaceans. Of the total number 

 of 305 animal species, 165 belong to the Mediterranean and 75 species are 

 Caspian relicts. 



In recent years, as a result of the increase in the salinity of the Sea of Azov, 

 a migration into it of Black Sea forms has begun. Thus a form of the genus 

 Teredo, which had not hitherto penetrated farther than the Kerch Strait, 

 has been found off Kazantip. On the other hand, the movement of more salt- 

 loving forms from the Utlyuksky inlet and the Sivash into the Sea of Azov 

 has also been observed. The qualitative composition of the population of the 

 Sea of Azov is a biological factor of exceptional interest. It includes several 

 heterogeneous groups. 



The relicts of the Novo-Euxine Caspian fauna, now populating the least 

 saline parts of the Sea of Azov and the eastern part of the Gulf of Taganrog 

 (river mouths, inlets), provide some species which propagate throughout the 

 whole Sea. To these relicts belong, among the coelenterates : Ostroumovia 

 maeotica and Cordylophora caspia ; among the polychaetes : Hypania invalida, 

 Hypaniola kowalewskyi and Manayunkia caspica ; among the molluscs : Mono- 

 dacna colorata, Dreissena polymorpha and Theodoxus pallasi ; among the Cu- 

 macea : Pterocuma pectinata ; among the mysids : Mesomysis kowalewskyi ; 

 among the amphipods : Cordiophilus baeri, Gmelina kusnetzowi, Dikerogam- 

 marus villosus, D. haemobaphes, Chaetogammarus ischnus, Pontogammarus 

 robustoides, P. weidemanni, P. crassus, Amathillina cristata, Calanus curvispi- 

 num, C. maeoticus, Pontogammarus maeoticus, and others. The last named 

 evidently now finds the best conditions for its existence in the Sea of Azov. 

 Fresh-water fauna in considerable numbers are mixed with this relict fauna in 

 the least saline parts of the Sea. 



The main mass of the fauna of the Sea of Azov consists, however, of Medi- 

 terranean immigrants ; some of them have found exceptionally good condi- 

 tions for mass development in the Sea of Azov. Among them the following 

 should be noted first of all: Balanus, Cardium, Mytilaster, Syndesmya, 



