Temperature and interspecific competition alter the impacts of two invasive crayfish species on a key ecosystem process

Abstract

Climate change is expected to alter impacts of invasive alien species (IAS). As omnivores and ectotherms, invasive crayfish species (ICS) can be particularly influenced by altered thermal regimes with possible impacts on native species and key ecosystem processes, such as leaf-litter breakdown. We performed a controlled study using a multi-trophic approach to assess the individual and combined effects between two ICS (Pacifastacus leniusculus and Procambarus clarkii) on leaf-litter breakdown under temperature increase (15 and 18 °C). We used aquaria with one or two species combinations of ICS (2-individuals per aquarium); each aquarium contained transparent cages with three individuals of a native invertebrate detritivore (Sericostoma sp.). All aquaria had a fine-mesh bag containing microbially-colonized oak leaves to assess direct and indirect impacts of crayfish on leaf-litter breakdown and fine particulate organic matter (FPOM) production. Leaf-litter breakdown driven by microbes and Sericostoma was affected by temperature. Increasing temperature enhanced leaf-litter breakdown and FPOM production by P. clarkii, but not by P. leniusculus. At 15 °C, leaf breakdown was lower in treatments with both ICS than the expected from their individual performances, which may suggest competitive interactions between crayfish species. FPOM production was significantly correlated with leaf-litter breakdown, but not in treatments with both ICS. Our results suggest that competitive interactions between ICS may occur and potentially attenuate their impacts on key ecological processes. However, predicted increases in temperature may change the performance of IAS and increase the magnitude of their combined effects.