Ecological importance of crayfish claws in consumption of mobile benthic prey

Trophic interactions are a critical component of ecosystem stability, governing prey-predator relationships. Crayfish are involved in numerous interactions within freshwater communities and, when non-native, they can negatively impact the structure and dynamics of ecosystems. During biotic interactions or unsuccessful molts, they are able to autotomize one or more claws, which can lead to changes in ecological performance among individuals. Because crayfish claws play an important role in feeding behavior, this creates an overlooked biotic context that could influence trophic interactions and impact on prey communities. It has been shown previously that crayfish claws have a minor role in predation of slow, soft prey, but their function concerning fast hard-bodied prey remains poorly studied. Here, we investigate whether the number of claws on marbled crayfish Procambarus virginalis modulates its ecological impact (focusing on predation rate) using functional response analyses against more mobile hard-bodied prey. We showed that the number of claws in P. virginalis significantly influenced the rate of predation on the prey Gammarus fossarum, with crayfish with two claws exhibiting a higher attack rate and lower handling time than clawless individuals. In addition, we found that non-trophic interactions increased with prey density, with generally antagonistic interactions between crayfish that reduced prey risk irrespective of claw presence. The influence of biotic contexts such as claw presence, prey density and prey type, as well as consumer density, should be considered in inferences of trophic and non-trophic interactions, as well as ecological impacts of invasive species.