Bivalve Mya arenaria L. as a model object in demecology: dynamics of bed structure, mortality and growth in the Kandalaksha Bay of the White Sea

The structure dynamics of Mya arenaria beds in the Kandalaksha Bay of the White Sea was observed for 7-35 years. We aimed to identify the patterns of the spatial-temporal organization of the clam beds by studying recruitment, growth, and mortality. Gaps between successful bed recruitment could exceed 10 years. The results of our investigations mostly support the hypothesis that the fluctuations in the recruitment level were determined both by the intensity of intraspecific relations and by the spat survival during the first year of life. Group growth rate and average annual mortality rate of soft-shell clams were sensitive to environmental conditions, which means they can be used as an indicator of their changes. M. arenaria in the most silted biotopes was characterized by the slowest growth and the highest mortality. However, the internal heterogeneity of the beds in terms of the ecological properties of individuals was high. The variation of the individual growth rate within the beds was comparable with that of the group growth rate between the studied locations. M. arenaria mortality rate varied with age. It is assumed the clam survival depends mostly on the degree of protection, intraspecific relationships, and aging.