Sex-specific predation of the non-native invasive American blue crab Callinectes sapidus on the Mediterranean mussel Mytilus galloprovincialis

The non-native invasive American blue crab Callinectes sapidus Rathbun 1896 is spreading across the Mediterranean Sea, endangering native communities, fisheries, and aquaculture. Yet, knowledge on its predation efficacy in the non-native range remains limited, and little is known about potential sex-specific differences in functional responses. This study presents the first functional response analysis of C. sapidus outside its native range, comparing male and female crabs preying on the Mediterranean mussel Mytilus galloprovincialis Lamarck 1819. Females showed a higher proportion of killed mussels, and a higher proportion of eaten mussels at lower prey densities. Both sexes exhibited a type II functional response, with high attack rates and short handling times, indicating destabilizing effects on prey populations, as observed in other invasive crabs. While attack rates and handling times did not significantly differ between sexes when considering total prey killed, females showed higher attack rates when considering only eaten prey. This result reflects density-dependent differences in prey consumption, whereby females fully exploit prey more frequently at low prey densities. Functional Response Ratios revealed that female crabs exerted more than twice the predatory pressure of males. These findings are consistent with the greater energetic requirements of adult female blue crabs associated with reproduction and migration and demonstrate how incorporating sex-specific comparisons can improve predictions of the impacts of non-native species.