Pan-Arctic population of the keystone copepod Calanus glacialis

The copepod Calanus glacialis is endemic to the Arctic Ocean and peripheral seas and forms a key component of the Arctic marine ecosystems. It is the major contributor to zooplankton biomass, a predominant grazer, and an important prey for seabirds, and fish. As for a planktonic species, its dispersal is expected to be widespread and mediated by ocean currents. However, complex circulation patterns and the existence of semi-enclosed fjords and seas in the Arctic can be hypothesized to influence the population genetic structure of this species. In this study, we aimed to infer patterns of connectivity between populations of C. glacialis distributed around the Arctic and across putative barriers formed by oceanographic currents and semi-enclosed fjords and seas. To achieve this, we used 11 polymorphic microsatellite loci to genotype 189 individuals from 7 locations: Svalbard fjords (Kongsfjorden, Hornsund, Isfjorden, Rijpfjorden, and Storfjorden), White Sea, and Amundsen Gulf, thus providing greater genetic resolution over a larger biogeographical scale than in previous studies. The results revealed a lack of structure among all seven locations around the Arctic, indicating a panmictic population with large-scale gene flow. This study also supports the hypothesis that the planktonic fauna of the White Sea is not isolated from that of the other Arctic regions.