BIOCOENOSIS OF MYA ARENARIA (LINNAEUS, 1758) IN THE KERCH STRAIT (AZOV AND BLACK SEA BASIN)

The bivalve mollusk Mya arenaria is a species recently introduced to the Azov and Black Sea Basin. Presently, it has become one of the dominant species in the Kerch Strait. Its biocoenosis keeps to silt and silty shell bottoms and comprises 13 animal species. The species density varies from 1 to 10 species/0.1m2 with 5.0±0.3 species/0.1m2 being the average value. In terms of species richness, bivalve mollusks are the most prevalent. The abundance is in the range from 40 to 2620 ind./m2 with 590±130 ind./m2, on average. The biomass ranges from 58 to 1599 g/m2; it is 770±67 g/m2 on average. The bivalve mollusks are the most prevalent in terms of abundance and biomass. A sizable part of the abundance belongs to crustaceans. The dominant species account for an average of 6 to 11 % of the total abundance and 78 to 85 % of the overall biomass. In general, the species composition of the biocoenosis on various substrates is characterized by a rather high degree of similarity. When the biocenosis dominated by Cerastoderma glaucum transformed into a M. arenaria one, the species richness decreased by 3.5 times, while the species density was relatively unchanged. The total abundance of the biocoenosis remained constant. The total biomass increased by 3.8–5.9 times due to the soft-shell clam (sand gaper) biomass. Then, upon the transformation of M. arenaria biocoenosis into Anadara kagoshimensis one, the species richness increased by 3.8 times and the species density increased by 1.5–2.0 times. Along with that, the total abundance and total biomass of the biocoenosis remained statistically the same. In terms of species richness, all three biocoenoses had the same core species. The changes in the species composition mainly resulted from the changes in rare species. Transformation of the biocoenoses occurred mostly due to the introduction of invasive species which took the leading position within the biocenotic community. In fact, there was a successive replacement of dominant species. The biocoenosis of M. arenaria in the central part of the Kerch Strait is an intermediate one between the biocoenoses of lagoon cockle and half-crenated ark.