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



Nereis diversicolor lives mainly in the Gulf of Taganrog, N. succinea in the 

 rest of the Sea. The variant N. diversicolor-Ostmcoda lives in the Gulf of 

 Taganrog all the year round. N. succinea possesses a more intensive faculty for 

 spawning than N. diversicolor ; it forms large numbers of eggs and it has some 

 pelagic larvae and heteroneroid forms. N. succinea probably pushes its rival 

 N. diversicolor out of the Sea of Azov into the Gulf of Taganrog, which is not 

 suitable for N. succinea owing to its low salinity. In the Black Sea, however, 

 with a salinity too high for N. succinea, N. diversicolor develops intensively, 

 forming powerful populations, and competes successfully with another 

 species — N. cultrifera. 



Clamworms form excellent food for many fish of the Black and Azov Seas. 

 Ninety per cent of them are assimilated by fish, compared with only 77 per 

 cent of crustaceans, 85 per cent of fish and only 29 per cent of molluscs. The 

 high content of nitrogen (64 per cent) and fats (16 per cent) in clamworms 

 also increase their value as food. 



As is known, Nereis of the Sea of Azov has been used for acclimati- 

 zation in the Caspian Sea in order to increase the feeding value of the 

 benthos for fish, primarily for the sturgeon. The results of this acclimatiza- 

 tion are given in Chapter II. Naturally, since Nereis has developed hugely in 

 the Caspian Sea, that system of competitive relationships with the local benthos 

 is of great interest. May Nereis do real harm to the benthos population of the 

 Caspian Sea? The system of synecological interconnection established for 

 Nereis in the Sea of Azov is of interest for the solution of this problem. 

 This has been comprehensively studied by I. Stark (1959). The latter confirms 

 the well known fact that Nereis succinea and N. diversicolor, like many other 

 nereides, thrive on ooze and vegetable detritus, and that they may take live 

 components of zoobenthos only accidentally and passively, together with their 

 main food, and that therefore they do no substantial harm to the rest of the 

 infauna, oligochaetes and chironomids included. Stark finds proof of this in 

 the frequency of the occurrence of dense nereides colonies within the areas 

 of high indices of the number of specimens and biomass of those more passive 

 forms of infauna which could have suffered from the nereides. Thus in the 

 Gulf of Taganrog, where the nereid biomass is highest, chironomids, oligo- 

 chaetes and Hypaniola reach their greatest development. 



The Pontogammarus maeoticus biocoenosis — The only relict, and the most 

 oligo-mixed, biocoenosis found throughout the whole of the Sea of Azov, 

 apart from the Gulf of Taganrog, on sloping sandy beaches, right at the 

 water's edge and within the regularly washed zone, is Pontogammarus maeo- 

 ticus. The biomass and number of organisms in this biocoenosis varies greatly, 

 reaching occasionally (in places with broken sea-weeds and detritus) 80,000 

 specimens of P. maeoticus per 1 m 2 , with a biomass of 642 g/m 2 . P. maeoticus 

 does not tolerate an accumulation of rotting sea- weeds since it is a steno-oxy- 

 biotic form. P. maeoticus is also rare on pure sand. In unfavourable weather 

 (strong swell, gales) and in winter time the whole mass of P. maeoticus 

 migrates into deeper waters. This form is found up to 10 m deep as a com- 

 ponent of almost all biocoenoses of the Sea of Azov. 



The Cardium edule biocoenosis — The Cardium edule biocoenosis begins 



