Interrelationships between the pelagic fauna of the White and Barents seas were studied on the basis of populations of dominant planktonic copepods inhabiting both seas. The analysis of distribution patterns and life cycles and environmental conditions in the White Sea allowed one to distinguish different types of populations with respect to an exchange of individuals between two neighboring seas. The White Sea populations of Calanus glacialis, Metridia longa, Centropages hamatus, and Temora longicornis are considered to be independent. They are able to complete the life cycles and maintain themselves within the White Sea without advection of individuals from outside. These species are absent or seldom occur in the Gorlo of the White Sea during some seasons. C.finmarchicus belongs to another category of species, which penetrate to the White Sea with Barents sea water. It is not able to complete the life cycle due to inappropriate environmental conditions and a quite low abundance. A few individuals of such pseudo-populations occur in the Gorlo, White Sea basin and bays. The species of the third category, e.g. Pseudocalanus minutus, are numerous in both seas. They form subpopulations or are part of more complex population inhabiting both seas. They are independent and able to complete their life cycles successfully. The possibility of exchange and mixing between them cannot be excluded. Various mechanisms underlay and support the independence of the local White Sea copepod populations, but the specific hydrophysical regime of the Gorlo is obviously important for their partial isolation from the Barents Sea populations.
