Climate change and competition by the invasive Atlantic blue crab represent a critical threat for the Mediterranean green crab

Biological invasions are a main threat to the integrity of marine ecosystems and a major driver of biodiversity loss. The Mediterranean Sea is an enclosed basin, and its habitats are particularly vulnerable to climate change, which, in turn, is expected to exacerbate the negative effects of biological invasions. In this study, we applied Species Distribution Models to project current and future species’ distribution and habitat suitability for the Mediterranean green crab Carcinus aestuarii and the invasive Atlantic blue crab Callinectes sapidus within the Mediterranean basin. Subsequently, the models were also run factoring the effect of indirect competition by the Atlantic blue crab on the green crab’s habitat and range distribution. Our hypothesis was that C. sapidus would expand its geographic distribution under a climate change scenario, while C. aestuarii would be negatively affected by the double effect of climate change and exploitative competition with the invasive blue crab. The results obtained combining the pressure exerted by climate change and the invasive competitor predicted a rapid decline in the distribution of suitable habitat for the Mediterranean green crab, eventually leading to the extirpation of this species from its native range. In contrast, environmental conditions are expected to remain favourable for the Atlantic blue crab along most of the Mediterranean coastlines. Our models raise concern about the fate of the Mediterranean green crab and call for an effective management of invasive marine species and powerful climate change mitigation actions to limit a critical loss of biodiversity in the Mediterranean Sea.