Reproduction features of ocean quahog, Arctica islandica (Linnaeus, 1767), in the White Sea

The gametogenic cycle of ocean quahog, Arctica islandica, was investigated using specimens collected from a near-shore bed (10–15 m deep) in the Kandalaksha Bay of the White Sea during five summer seasons (1983, 1984, 2011, 2015, 2017). At present, the White Sea is the eastern distribution boundary of this mollusk. Local environmental conditions there differ considerably from those in other parts of its range, and many characteristics of the quahog populations in the White Sea are still poorly understood. In this study, we examined gonads from 384 ocean quahogs with shell length over 30 mm prepared with the use of standard histological techniques. The results showed that the reproductive cycle features of A. islandica in the White Sea were generally similar to those in other parts of its distribution. Clams in the spawning state were found mainly from the second half of July to October at a near-bottom water temperature of 9–15 °C. Both average (60–70 μm) and maximum (92–95 μm) size of mature oocytes of ocean quahogs from the White Sea were similar to those in North Atlantic populations. At the same time, we noted substantial interannual shifts in the spawning activity of A. islandica and showed that they reflected interannual changes in hydrological characteristics. However, it is unlikely that these shifts may affect the overall recruitment success of the population of this species.