Is a rapid expansion of the invasive amphipod Gammarus tigrinus Sexton, 1939 associated with its niche selection: a case study in the Gulf of Finland, the Baltic Sea

Among the recent non-indigenous species the gammarid amphipod Gammarus tigrinus is one of the more aggressive invaders in the Baltic Sea. Quantitative sampling of the shallow water habitats of the Gulf of Finland showed that G. tigrinus has become established in the whole coastal zone of the Gulf. Boosted Regression Trees modelling indicated that the abundance and biomass of G. tigrinus varied as a function of wave exposure, water salinity and transparency, with the invasive amphipod having higher abundance and biomass at less exposed, more dilute, and more turbid sites. Gammarus tigrinus appears to be competitively superior to the native gammarids, possibly leading to further decline of the native gammarid populations in the Gulf of Finland.