Distribution, population structure and salinity tolerance of the invasive amphipod Gmelinoides fasciatus (Stebbing) in the Neva Estuary (Gulf of Finland, Baltic Sea)

In the early 1970s, the Baikalian amphipod Gmelinoides,fasciatus (Stebbing) was intentionally introduced into several lakes in the Gulf of Finland basin in order to enhance fish production. By 1996, G. fasciatus successfully colonized the littoral zone of Lake Ladoga and, via the Neva River, invaded the Neva Bay, the freshwater part of the Neva Estuary. In 1999, G. fasciatus was first registered in the inner Neva Estuary, the very first record of the Baikalian amphipod in brackish waters of the Baltic Sea. Distribution, abundance, reproduction and population structure of G.,fasciatus in the Neva Estuary were studied during 1998-2000. In some locations of the Neva Estuary, maximum densities of G. fasciatus reached 3500 ind. m(-2). In general, density and biomass of G. fasciatus in the freshwater part of the Neva Estuary were higher (around 1.5 fold) than in the brackish-water part. Fecundity of this amphipod averaged 10-20 eggs per female, depending on body size of females and season. In order to assess the possibility of further spread of G.,fasciatus in the Baltic Sea, the salinity tolerance of this species was determined in a series of laboratory experiments. Our results showed that the invasive amphipod G. fasciatus is potentially able to colonize shallow coastal habitats of, for example, the Gulf of Bothnia, Gulf of Riga and other parts of the Baltic Sea with water salinities ranging from 1 to 5 psu.