Penetration of Pacific zooplankton into the western Arctic Ocean tracked with molecular population genetics

Calanus glacialis is an ecologically important marine copepod found throughout the Arctic Ocean with limited distributions in the North Pacific and North Atlantic Oceans. We employed molecular techniques to determine the population genetic structuring of C. glacialis across the boundaries of these 3 oceans. Examination of the DNA sequence of the 16S ribosomal RNA gene identified 2 predominant haplotypes which defined the Arctic and North Pacific (Bering Sea) populations. Advection from the Bering Sea into the Arctic as far as the western Canada Basin was detected, but C. glacialis from the Bering Sea was absent in the majority of Arctic Ocean samples. This indicates that C. glacialis from the Bering Sea was not reproductively established in the Arctic Ocean. Genetic divergence of Arctic and Bering Sea populations may have occurred during their isolation in the course of the Pleistocene glaciations, or, more recently, from unidirectional advection due to the northward current regime through the Bering Strait. Climate warming will increase opportunities for southern organisms to become established in the Arctic Ocean. The study of intraspecific genetic variation of C. glacialis has great potential in aiding the early detection of such ecological change.