Predatory impact of the freshwater invader Dikerogammarus villosus (Crustacea: Amphipoda)

Abstract: To assess the increasing threats to aquatic ecosystems from invasive species, we need to elucidate the mech-anisms of impacts of current and predicted future invaders. Dikerogammarus villosus, a Ponto–Caspian amphipod crus-tacean, is invading throughout Europe and predicted to invade the North American Great Lakes. European field studies show that populations of macroinvertebrates decline after D. villosus invasion. The mechanism of such impacts has not been addressed empirically; however, D. villosus is known to prey upon and replace other amphipods. Therefore, in this study, we used microcosm and mesocosm laboratory experiments, with both single and mixed prey species scenar-ios, to assess any predatory impact of D. villosus on a range of macroinvertebrate taxa, trophic groups, and body sizes. Dikerogammarus villosus predatory behaviour included shredding of prey and infliction of “bite ” injuries on multiple victims. Dikerogammarus villosus killed significantly greater numbers of macroinvertebrates than did the native Gammarus duebeni, which is currently being replaced by D. villosus. This invader thus appears to impact on freshwa-ter ecosystems through its exceptional predatory capabilities. We predict that future invasions by D. villosus will have serious direct and indirect effects on freshwaters, with its invasion facilitated in a larger “invasional meltdown ” in re-gions like the North American Great Lakes. Résumé: Pour évaluer la menace grandissante que représentent les espèces envahissantes pour les écosystèmes aquati-ques, il est nécessaire d’élucider les mécanismes par lesquels les envahisseurs actuels et ceux qu’on prévoit dans le fu