The boreal bivalve Arctica islandica is a model organism for long-term observations and a promising indicator of environmental conditions due to its wide distribution and exceptional longevity. In the White Sea, the eastern border of the range, the ecological characteristics of the populations of A. islandica are understudied despite its almost ubiquitous distribution in the region. The bed of this species in the Kandalaksha Bay of the White Sea has been observed for nearly 35 years. In this study we investigated long-term changes in size-age composition as a reflection of the patterns of recruitment, growth and mortality. Our findings suggest that A. islandica beds in the White Sea are characterized by long-term gaps in successful recruitment. As a consequence, aggregations of almost same-aged clams are formed, and their structure remains relatively stable for many years. This long-term stability of the bed structure is not the result of sustainable loss replacement but rather a reflection of the ecological characteristics of A. islandica at certain life stages, namely, a slow growth in individuals older than 10 years (approximately 1 mm year− 1) and relatively low mortality (9% a year). Interannual fluctuations in bed recruitment may be associated with intraspecific relationships between adults and juveniles and with survival of clams at the early stages of ontogenesis. Compared to other regions of its distribution, A. islandica in the White Sea has the smallest maximum size (around 50 mm) and the shortest lifespan (approximately 50 years).