THE SEA OF AZOV 



Table 222 



533 



9,540 in May-June, 19,184 in July, 9,161 in August, 5,910 in September and 

 6,412 in November (an annual average of 26,063). Consequently there are 

 two maxima in plankton development : in spring and autumn. 



Benthos 



Summer suffocation of the Sivash bottom-fauna in calm weather is a common 

 occurrence; as a result, the deeper-lying mud beds are much more sparsely 

 populated. Summer, moreover, is the least favourable season for the develop- 

 ment of bottom-fauna ; winter and especially spring are the most favourable. 

 As a result, seasonal changes in benthos biomass in the Sivash are observed 

 on mud bottoms in the deeper parts : a decrease from summer to autumn as a 

 result of suffocation, further winter reduction, and an increase in the spring (a 

 further drop in the spring may in certain cases be caused through consump- 

 tion of it by fish). 'The fact that sand and a mixture of silty sand and shell 

 gravel are the most productive soils in the northern Sivash is explained by 

 the same reasons, i.e. in the last analysis by the aeration conditions at the 

 bottom.' 



Among the large forms of the benthos only Chironomus salinarius and fly- 

 larvae are found on the muds in the central and southern parts of the Sivash. 

 Macrobenthos is absent from coarse-grained soils, while the fly larvae are 

 adapted best to silty sand with shell gravel ; the anaerobic conditions of mud 

 soils are not favourable to them. Here the biomass is very small, fluctuating 

 between 1 and 12 g/m 2 . In the most saline part (60% o ) it drops to a few grammes 

 or fractions of a gramme. 



Phytobenthos presents a different picture since the inner parts of the bay 

 are considerably overgrown with the ultrahaline Cladophora siwaschensis, 

 which is absent from the outer parts of the bay. The increase of the amount of 

 phytobenthos at a chlorine content of 20 to 40% o is explained by the intensive 

 development of Zostera and Ruppia under these conditions. 



Of the nine bottom-communities established for the Sivash the following 

 are the most numerous: Cardium, Syndesmya, Hydrobia, Chironomus, 

 Artemia and Cladophora. 



