The effects of climate change on European distributions of four alien marine crab species

Abstract. Widely recognized as a major threat to marine biodiversity, invasive species have become a fundamental global concern. With over 500 alien species identified in the Mediterranean alone, European seas are particularly susceptible to the potential ecological and economic threats of invasives. The rate of marine species introductions in the European Union (EU) continues to increase, with climate change facilitating their spread and impact. Crabs and other crustaceans are among the most successful groups of marine invasives and can have significant negative ecological and economic impacts where they become established. To assess the ecological and economic threats posed by these species and to develop monitoring, early response, and mitigation plans, it is important to be able to determine which areas are at highest risk of further range expansion, especially under expected climate scenarios. We studied the current and future distributions of four predatory brachyuran crabs that were previously identified as species of concern for European seas, namely Hemigrapsus sanguineus, Charybdis longicollis, Matuta victor, and Portunus segnis, under various climate change scenarios. Species distribution models were built using an ensemble modelling approach. The results show that the potential distributions for all species are much larger than the current known distributions. Under all predicted climate change scenarios, the climatic conditions for P. segnis, C. longicollis, and M. victor, in particular, are expected to improve in most of the Mediterranean Sea, resulting in an expansion of suitable habitat. The Adriatic and Aegean seas are of particular concern as results indicate that these seas are not only highly suitable under current climatic conditions but also will become more suitable under all climate scenarios. It is, therefore, important to further investigate potential impacts, to increase monitoring, and to explore possible management strategies for these seas in order to manage the invasion of these species and avoid future biodiversity and economic losses.