THE SEA OF AZOV 531 



Phosphorus and nitrogen 



A further characteristic is the insignificant content of phosphates and nitrates 

 in Sivash waters which was noted by Vorobieff. Only in winter has an appre- 

 ciable accumulation of these substances been recorded. 



Soils 



According to Vorobieff the prevailing soils are ' muds of varying colour and 

 density, with an admixture of sand, shell gravel and organic remains. These 

 muds are mainly composed of huge amounts of plant remains, detritus and 

 plankton, which dies off in salt water, brought from the Sea of Azov and the 

 Utlyuksk inlet (autochthonous matter) and also of the plants of the Sivash 

 itself, which develop in huge masses. In the northern part the mud consists 

 of dead ditch-grass, Zostera, dog whelk and the green algae Cladophora ; in 

 the central and southern Sivash it consists of Cladophora and green-blue algae. 

 The small crustacean Artemia salina, which develops in enormous numbers in 

 the summer, must play an important role in mud formation of the southern 

 Sivash.' The processes of the decay of organic substancesare limited owing to 

 the high salinity and large amounts of organic matter deposited among the 

 bottom sediments. 



'Organisms most tolerant of hydrogen sulphide, methane and other gases 

 liberated during the processes of decay, such as Sphaeroma, Idothea, Gam- 

 marus, the fly larvae, nemertines and others, are found in huge quantities 

 among decaying sea-weeds on the shores of the Sivash.' 



Spionidae, Pectinaria, Syndesmya and Cardium are found in muddy sand, 

 and Clymene, Nereidae, Syndesmya, Cardium, Hydrobia, Chironomidae and 

 others in muds. 



Distribution and composition of fauna ' 



Vorobieff (1940) has made a comprehensive study of the distribution of life in 



the Sivash, and we shall be using his data below. 



As one moves up into the bay there is a change in the qualitative compo- 

 sition of the fauna with the increase of salinity — the marine forms become less 

 numerous and the number of the typical ultrahaline forms increases (Figs. 252 

 and 253). 



Huge amounts of plankton and larval forms of benthos are constantly 

 brought into the Sivash by the Azov Sea waters ; a kind of compulsory coloni- 

 zation of the Sivash is going on. Most of the larvae and adult organisms 

 which find themselves in the Sivash either perish, or live for only a short time, 

 or settle in the Northern Sivash. We have every reason to assume that if it 

 were not for this constant influx of Azov Sea forms the population of 

 the Sivash would be much poorer in variety and biomass, since most of the 

 species which survive in the Sivash have a very low productivity and a sharp 

 decrease in their biomass occurs throughout most of the year. 



At the present time only the ultrahaline species five in the central and 

 southern Sivash. The Novo-Euxine and ancient Black Sea relicts are the first 

 to disappear as one moves into the Sivash, then the Azov-Black Sea species 

 and the fresh-water halophilic ones. 



