Geographic and temporal scales of connectivity among populations of marine organisms in the North Pacific

Understanding the spatial and temporal scales of connectivity between populations of marine organisms is important for defining units for management and conservation. Marine fishes and invertebrates generally differ from freshwater and anadromous species in having larger populations with greater potentials for gene flow. Nevertheless, shoreline topography, ocean fronts, and current systems can regulate connectivity between marine populations over multiple time scales. Decadal shifts in ocean-climate regimes often lead to changes in local abundances. Over longer periods, Pleistocene glaciations severed connections between populations of many species currently distributed across the North Pacific. Divergences are still apparent in some species (e.g., walleye pollock, Pacific cod, Pacific herring), but not in others (Japanese snow crabs), reflecting the effects of ice-age isolation in one or more refugia in the North Pacific. Population extinction on one side of the Pacific and subsequent postglacial expansions tends to produce widespread genetic homogeneity, while multiple isolations across the North Pacific and subsequent re-association creates genetic discontinuities. Both patterns evident in contemporary populations indicate that they have not reached migration-drift equilibrium since the last deglaciations 10-15 k years ago. Periodic polar warming also facilitated trans-Arctic dispersals leading to geographically isolated conspecific populations in the North Atlantic and North Pacific.