Predation preference of signal crayfish (Pacifastacus leniusculus) on native and invasive bivalve species

Abstract

AbstractPredatory, non‐native fauna can influence biodiversity and trophic dynamics in invaded ecosystems. Signal crayfish (Pacifastacus leniusculus) are a highly successful invader, which have altered freshwater benthic communities, including bivalve populations. Bivalves are a keystone freshwater group in global in decline, partly due to invasion by alien bivalve and crayfish species. However, little is known about the predatory impacts of invasive crayfish within co‐occurring native and invasive bivalve populations. Mesocosm predation choice experiments considered relative signal crayfish predation rates between paired native (Anodonta anatina and Unio tumidus) and invasive (Dreissena polymorpha, D. bugensis, and Corbicula fluminea) bivalves, and between paired invasive bivalves. All bivalves were actively predated, but there was no consistent difference in the biomass of invasive versus native bivalves consumed. However, the effects of consumption were consistently different; 18.2% of invasive bivalves were lethally predated, with 100% of surviving individuals remaining undamaged, whereas 1.1% of native bivalves were lethally predated, but 100% of surviving individuals received nonlethal damage in the form of shell chipping, which could reduce long‐term bivalve fitness in natural environments. In experiments considering paired invasive species, D. polymorpha was more resistant to predation when compared to other invasive taxa tested. The majority of field research considering aquatic invasions considers purely lethal predation effects inferred from invertebrate presence/absence. These experiments demonstrate the need to better understand both the processes and impacts of predation by invasive species, which may include substantial nonlethal effects on the fitness and life history of endangered taxa.