The non-indigenous gammarid species Pontogammarus robustoides (G.O. Sars, 1894), Obesogammarus crassus (G.O. Sars, 1894), Dikerogammarus haemobaphes (Eichwald, 1841) and Dikerogammarus villosus (Sowinsky, 1894) are present in the Gulf of Gdańsk (Southern Baltic Sea). These species reached the Gulf of Gdańsk by 2010 near the point where the River Vistula flows into the Baltic Sea, and became constituents of the amphipods on the shallow bottom of the gulf. All the gammarid species found are of Ponto-Caspian origin. They have been able to move across Europe along rivers and canals, and inhabit reservoirs and drainage systems in the vicinity of such waterways. D. villosus is the latest gammarid species to have colonized Poland. The floods that afflicted Poland in May and June 2010 could have had a significant influence, intensifying as they did the inflow of water from the Vistula into the Gulf of Gdańsk. This could have accelerated the arrival of individuals of these species. The water salinity at the sampling stations was 5.8 – 6.1 PSU. The possible invasion of non-native gammarids may have important consequences for the benthic fauna communities in the Gulf of Gdańsk. |