Predatory impacts of the invasive ‘killer shrimp’ Dikerogammarus villosus on a resident amphipod and isopod (Crustacea: Malacostraca) are influenced by water quality and habitat type

Abstract

The Ponto-Caspian amphipod Dikerogammarus villosus has invaded Central European and British freshwaters and its arrival is associated with biodiversity decline, as D. villosus is predatory towards many macroinvertebrate taxa, including resident amphipods such as Crangonyx pseudogracilis and isopods such as Asellus aquaticus. I investigated how differential physiological tolerance, habitat use and predation may drive coexistence or exclusion among D. villosus and resident ‘supertramp’ prey such as C. pseudogracilis. Experiments revealed that D. villosus could not survive 12 h in the extremely poor water qualities that C. pseudogracilis and A. aquaticus commonly live. Experiments manipulating oxygen levels, revealed low survivorship of C. pseudogracilis and A. aquaticus in the presence of D. villosus at higher oxygen levels but this survivorship increased significantly as oxygen levels fell. Predation of C. pseudogracilis by a resident amphipod Gammarus pulex followed a similar pattern but was much less severe and A. aquaticus appeared resistant to G. pulex predation. Mesocosm experiments showed that C. pseudogracilis survivorship in the presence of D. villosus increased when dense vegetation was present compared to bare substrate. Survivorship of A. aquaticus was uniformly poor in all habitats. Taxa with high environmental tolerance and adaptability may be resistant to this invader’s worst impacts.