Temperature and salinity jointly shape predation by the invasive blue crab Callinectes sapidus: an experimental study in a Mediterranean lagoon

Climate change is altering trophic interactions in coastal ecosystems through changes in temperature and salinity. Understanding these effects is essential to predict future impacts of invasive predators in Mediterranean lagoons. In this study, we experimentally investigated how temperature and salinity affect predation by the invasive blue crab Callinectes sapidus on the clam Ruditapes philippinarum in the Berre Lagoon. Predation experiments were conducted across ecologically relevant temperature and salinity gradients. We quantified prey consumption, biomass intake, and shell breakage to assess trophic performance. Predation activity was primarily driven by temperature, while salinity exerted a secondary modulatory effect across the thermal gradient. Feeding was strongly limited below 16–18 °C, where more than 50% of crabs did not feed regardless of salinity, defining a clear “no-predation niche”. Above this thermal threshold, predation rates increased markedly with temperature, reaching maximum values under warm conditions associated with low to intermediate salinity levels, whereas hypersaline conditions reduced feeding activity. Biomass consumption followed a similar pattern, with crabs consuming up to 80 ± 15 % of their body mass in clam biomass per day under the warmest and lowest salinity conditions. The proportion of broken shells decreased with increasing temperature, which may reflect changes in feeding behavior under warmer conditions. We developed a predictive model linking temperature, salinity, and predation rates. Application of this model to long-term environmental monitoring data from the Berre Lagoon revealed strong seasonal variability in predicted predation rates, with maximum predation occurring during summer periods characterized by high temperatures. Spatial analyses further identified localized zones of elevated predation risk within the lagoon. Seasonal warming may amplify predation pressure by C. sapidus on clam populations, increasing its ecological impacts in Mediterranean lagoons.