Predicting the potential distribution of the Lessepsian blue swimmer crab Portunus segnis in the Mediterranean Sea

The portunid blue swimming crab Portunus segnis (Forskål, 1775) is one of the earliest Lessepsian invaders, recorded in Egypt 30 years after the completion of the Suez Canal in 1868. Subsequently, it has successfully established in coastal habitats of the Levantine basin, the Aegean Sea, and more recently, Tunisian coastal waters. Here, records of P. segnis in the Mediterranean Sea and in native habitats were collated, georeferenced, and matched to high resolution oceanographic environmental layers. Environmental Niche Modelling (ENM) procedures were implemented to identify the main environmental factors driving the species occurrence in invaded habitats and define its Grinnellian niche. To predict the future distribution of the crab, its niche was projected into a mid- and high-severity future climate scenarios for 2050. The results showed that P. segnis, after invading the Mediterranean Sea, settled in areas characterized by abiotic conditions considerably different from those showed by native habitats. ENM procedures indicated maximum salinity and, to a minor extent, mean surface water temperature, as the main factors regulating the distribution of the species in the Mediterranean Sea, ultimately confirming for the southern sectors of the basin a high habitat suitability for the crab. Projections to 2050, in particular under the high-severity scenario, clearly indicated an northward expansion of P. segnis towards areas currently invaded by the Atlantic blue crab Callinectes sapidus. The possible outcomes of the co-occurrence of P. segnis and C. sapidus, in terms of competitive interactions as well as impacts on invaded coastal ecosystems, are considered