Seaweed Biogeography of the North Atlantic: Where are we now?

Reconstructions of the glacial distribution areas of individual species belonging to the various seaweed regions, lead to the conclusion that species belonging to the Arctic-cold temperate N Atlantic flora could have been faced with such an extreme reduction of their distribution area (especially in the NW Atlantic) that they were threatened with extinction. Such severely adverse conditions did not exist in the N Pacific, and this may explain the much greater richness of the cold-temperate N Pacific flora. Laminaria hyperborea possibly exemplifies species that became extinct in the NW Atlantic during the glaciations, but survived in the NE Atlantic. Species in other seaweed regions than those in the Arctic-cold temperate N Atlantic were probably much less affected by the Pleistocene glaciations. Species endemic to the NW Atlantic coast, such as Grinnellia americana, are eurythermous and could potentially inhabit a broad area along NW African coasts and in the Mediterranean. Its absence there indicates that the central Atlantic Ocean can function as a barrier to long distance dispersal.