Invasion of the North American Amphipod ( Gammarus tigrinus Sexton, 1939) into the Curonian Lagoon, South-Eastern Baltic Sea

Abstract

The North American amphipod (Gammarus tigrinus Sexton, 1939) was found in the Lithuanian part of the Curonian Lagoon in September 2004. In the littoral part, the distribution of the species was restricted to the area of seawater inflows, within a distance of up to 23 km upstream from the sea. The species was present in all types of the habitats sampled (reeds, mixed and soft bottoms) and its distribution showed a continuous rather than fragmented pattern. In most cases, the species was absent in enclosed depositional environments with mixed substrates and the presence of mud. Obessogammarus crassus (G. O. Sars) was the only crustacean species always found in the presence of the new invader G. tigrinus, whereas other species showed a higher degree of habitat discrimination within the stations. Along with the other two introduced crustaceans O. crassus and Pontogammarus robustoides (G. O. Sars), G. tigrinus showed the highest occurrence (79%) in the salinity range of its recent distribution in the lagoon. As the factors limiting the species establishment are difficult to predict, the rapid spread of G. tigrinus into inland Lithuanian waters might be expected.