THE SEA OF AZOV 



505 



one and a half times greater in autumn than in spring. The species invariably 

 accompanying M. Hneatus are, in order of decreasing importance, Balanus, 

 Cardium and Nereis succinea. In contrast to all the other biocoenoses of the 

 Sea of Azov, the M. Hneatus grouping is more stable and permanent. The 

 quantitative ratio of different species in this biocoenosis is given in Table 

 209. 



In the spring M. hneatus is represented in the biocoenosis by two age- 

 stages; the one-year-olds (on the average 4,904 specimens per 1 m 2 ) and the 



two-year-olds (374 specimens per 1 m 2 ). It begins to multiply in April and 

 ceases to do so in August. The two-year-olds breed in April ; in May and June 

 the one-year-olds also begin to multiply. In the autumn those under one 

 year also begin to breed (7,812 specimens per 1 m 2 ). During this time the 

 number of one-year-olds and two-year olds is reduced (2,890 and 108 speci- 

 mens per 1 m 2 ) as a result of their being eaten by fish (bullheads, golden shiner, 

 roach and the Acipenseridae). Thus, the loss of one-year-olds from May to 

 November is 2,014 specimens, and that of the two-year-olds 266 specimens 

 per 1 m 2 . 



It has been established that the losses suffered by the one-year-olds per 

 1 m 2 are 160-32 g; of the two-year-olds, 81-66 g; and of those under one year 

 338-75 g. These data were obtained by examination of the variations of M. 

 Hneatus from different places, by the calculation of losses due mainly to their 

 being eaten by fish, by the analysis of stomach-content of fish and by making 

 use of the average weight of molluscs of a certain size. The total amount of 

 all three age groups of M. Hneatus eaten by fish from May to November is 



