Invasive species in the Baltic Sea include round goby (Neogobius melanostomus), red gilled mud worm (Marenzelleria spp.) For a young sea like the Baltic Sea, the establishment of non-indigenous species is, to some extent, also a natural on-going process of succession and so far no non-indigenous species have resulted in the extinction of native species. Some non-indigenous species, such as Marenzelleria spp.,