Biogeographic borders in the Barents Sea based on species distributions of bryozoans. Average position of the border with 50:50% of Atlantic boreal and Arctic species numbers is indicated by the pink line, and the red and green lines indicate the extreme positions of the border in cold and warm periods respectively. Area III between them is the transitional zone between the Atlantic boreal and the Arctic regions. Thus, area I always has > 50% Atlantic boreal species, and area II always > 50% Arctic species (after Denisenko 1990).