The introduced dark false mussel, Mytilopsis leucophaeata (Conrad, 1831) has spread in the northern Baltic Sea.
The dark false mussel, Mytilopsis leucophaeata, has been found in very specific habitat in the Archipelago Sea (northern Baltic Sea) and now has spread. Between 2011 and 2015, we collected small numbers of M. leucophaeata at three sites 10 to 28 km apart in soft sediment habitats with pier structures and rocks in water 2-3 m deep. Previously, M. leucophaeata in the northern Baltic Sea was restricted to areas receiving cooling water discharge from nuclear power plants. Our findings were from areas without a source of heated water, and the closest known occurrence of M. leucophaeata is 120 km away. It is evident that this species is expanding its distribution in the Baltic Sea area and is not restricted to areas having anthropogenically-warmed water.