Title: Growth of Mya arenaria L. at the northern edge of the range: heterogeneity of soft-shell clam growth characteristics in the White Sea
Abstract: Linear growth of soft-shell clams, Mya arenaria L., was studied at six locations in the White Sea situated in the middle and low tidal zones. The main aim was to analyse the growth heterogeneity both within beds (with respect to individual growth) and between beds (with respect to group growth). Mya population was characterized by a slow growth and a long lifespan. Maximum shell size was 70–80 mm, and longevity was at least 25 years. In addition, growth rates were highly variable, statistically significant differences being present both within and between the beds. No differences were found in group growth between different tidal horizons of the same site. The slowest growth of soft-shell clams was observed at sites with the greatest content of fine particles (silt and clay) in sediments. Differences between beds in Mya group growth could reflect variability of feeding conditions, which were probably determined by some local features (e.g. hydrodynamic regime). However, the variation of the individual growth rate within beds was comparable to that of the group growth rate between studied locations. To a great extent it seemed to be determined by the characteristics of the initial period of soft-shell clam growth.