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



and Cardium, began to be observed. The exceptionally low floods of 1949 

 and 1950 evoked great changes in the benthos not only of the Gulf of Tagan- 

 rog, but also of the whole Sea of Azov. In the eastern part of the Sea the 

 Mytilaster biocoenosis almost completely disappeared, and, as I. Stark has 

 pointed out (1955), 'in 1951 more substantial changes occurred in the benthos 

 of the Sea of Azov than in the 15-year period since the work of Vorobieff and 

 the 25-year period since the observations of N. T. Tchougounov. The area 

 occupied by the Syndesmya biocoenosis (Syndesmya ovatd) was greatly 

 reduced, while that occupied by the Cardium . . . and Corbulomya (Corbu- 

 lomya maeotica) biocoenoses, situated hitherto mainly in the coastal zone, was 

 widened (Fig. 242) ... the Hydrobia (Hydrobia ventrosa) biocoenosis dis- 

 appeared and the new Nephthys (Nephthys hombergi and Actinia equina) 

 biocoenoses were formed.' The increase in the numbers of the polychaete 

 Nephthys hombergi is linked with a decrease in the numbers of Nereis and 

 vice versa ; this too can be considered the result of the silting of corresponding 

 areas of the sea-bed (Fig. 243). The total benthos biomass, however, did not 

 undergo any considerable changes, although in some individual areas the 

 changes might be considerable. All these changes depend on the volume of 

 the spring floods, on the variations and distribution of the soils of the sea- 

 bed, on the development of plankton, on the amount eaten by fish and on the 

 occurrence of suffocation. A change in these conditions can bring about a 

 suitable environment for the development at one time of filter-feeders, at 

 another of soil-eaters, in the latter case accompanied by an accumulation of 

 liquid mud soil. 



In the open part of the Sea of Azov the changes in salinity observed do not 

 affect to any considerable extent its benthos distribution. In the Gulf of 

 Taganrog salinity fluctuations are much more pronounced; they have a 

 great influence on the distribution of the bottom-fauna and on its biomass. 

 Marine species gain possession of the Gulf of Taganrog in years when the water 

 is low. An inverse dependence on the distribution of the benthos biomass is 

 observed for the western and eastern parts of the Gulf of Taganrog — an in- 

 crease of the benthos biomass in its western part corresponds to a decrease in 

 the eastern one (Fig. 244) (I. Stark, 1955). Stark thinks that a fall in the in- 

 flow from the river Don will not have a bad effect on the benthophage feeding 

 grounds in the Sea of Azov proper, in spite of a pronounced decrease in the 

 number of Syndesmya and an increase in that of Corbulomya Cardium and 

 Mytilaster. The Gulf of Taganrog will be more densely populated by Cardium, 

 Hydrobia, Nephthys and Syndesmya, but conditions for the feeding of the 

 young would deteriorate, since the habitats of the small-sized forms of in- 

 fauna (chironomids and Hypaniola) will be reduced ; for adult fish the deterio- 

 ration would be marked by a reduction in the numbers of Monodacna and 

 Dreissena. Changes, however, were observed in the Sea of Azov also ; with the 

 increase of salinity, salt-loving forms such as Actinia equina, Cardium exiguum, 

 Cylista viduata, Pectinaria neapolitana, Glycera convoluta, Melinna palmata, 

 Nassa reticulata, Cyclonassa kamyschensis and several others penetrate into 

 the basin through the Kerch Strait and the Utlyuksk inlet. The Teredo navalis, 

 hitherto unknown in the Sea of Azov, has been recorded off Kazantip. 



