Trends and drivers of ⁢Macoma balthica⁢ L. dynamics in Kandalaksha Bay, the White Sea

Long-term population dynamics of marine invertebrates can be shaped by environmental conditions as well as biotic factors, including predation, diseases, interspecific or intraspecific competition. Towards the northern edge of species ranges the role of biotic interactions gradually decreases while the impact of climate oscillations becomes more important. This study examined the long-term changes in abundance, individual growth rates and shell shape characteristics of Macoma balthica, one of the dominant species in White Sea soft-bottom intertidal communities. To test the role of predators in changes in clam abundance, we examined the number of moonsnails Amauropsis islandica. Macoma balthica exhibited spatially synchronous population dynamics at six sites in Kandalaksha Bay, where densities of clams varied between 140 and 8500 ind. m(-2) during the 21-year period of observations. Statistical modelling using generalized additive models (GAM) shows that a combination of mild winter and warm summer led to an increase in M. balthica density the following year. Predation by A. islandica had no impact on changes in M. balthica density. Growth rates of M. balthica were higher during a cool decade, but clams that lived in a wanner period were characterized by more globose shells. Our results suggest that the climate oscillations can be regarded as the key factor causing the shift in abundance of M. balthica in the White Sea during the last two decades via recruitment and survival.