Ecological traits of the amphipod invader Dikerogammarus villosus on a mesohabitat scale

Since 1995, Dikerogammarus Villosus SONVINSKI, a Ponto-Caspian amphipod species, has been invading most of Western Europe's hydrosystems. D. villosus geographic extension and quickly increasing population density has enabled it to become a major component of macrobenthic assemblages in recipient ecosystems. The ecological characteristics of D. villosus on a mesohabitat scale were investigated at a station in the Moselle River. This amphipod is able to colonize a wide range of substratum types, thus posing a threat to all freshwater ecosystems. Rivers whose dominant substratum is cobbles and which have tree roots along the banks could harbour particularly high densities of D. villosus. A relationship exists between substratum particle size and the length of the individuals, and spatial segregation according to length was shown. This allows the species to limit intra-specific competition between generations while facilitating reproduction. A strong association exists between D. villosus and other Ponto-Caspian species, such as Dreissena polymorpha and Corophium curvispinum, in keeping with Invasional Meltdown Theory. Four taxa (Coenagrionidae, Calopteryx splendens, Corophium curvispinum and Gammarus pulex) exhibited spatial niches that overlap significantly that of D. villosus. According to the predatory behaviour of the newcomer, their populations may be severely impacted.