Multiscale modelling of dispersal pathways for the invasive blue crab larvae (Callinectes sapidus) in the Mediterranean Sea

Abstract

The blue crab (Callinectes sapidus) is an invasive species that has occurred in the Mediterranean Sea since the mid twentieth century but undergone a significant population increase in the last decade. This worrying increase has raised concerns necessitating to provide information about its ecology and population dynamics at different scales, including its dispersal patterns. Biophysical modeling is a valuable tool for addressing the challenges associated to the study of marine species dispersal across various timeframes and geographical areas. To study the dispersal routes and connectivity of the blue crab in regions of the Mediterranean Sea where this invasive species has been observed, we used a biophysical modeling study, combining a Lagrangian tool with two hydrodynamic models of different spatial resolutions and geographical coverages but with the same period (2010 to 2020). We highlight the main larval dispersal routes, such as the recurrent connections between nearby coastlines including Tunisia and Sicily, as well as Sardinia, Corsica, and the Ligurian Sea coast, and their consistency, both across the entire Mediterranean Sea and a focus on its Northwestern part. The areas with the highest larval retention are revealed to be the Gulf of Lion, the Gulf of Gabès, the Adriatic Sea and the Levantine basin. Furthermore, the critical role of islands in the colonization dynamics of the blue crab is emphasized. Interconnected regions are identified, including Tunisia, Sicily, Sardinia, Corsica, and the coastlines of the Ligurian and Tyrrhenian Seas. Larval connectivity was determined to be high between the Eastern and Western Mediterranean basins, likely explaining the crab's rapid invasion into suitable habitats over the whole sea. In more isolated regions, such as the Adriatic Sea, highest self-recruitment rates were obtained. These findings provide valuable insights for the development of tools and visualizations that can assist managers and stakeholders in gaining a better understanding of the challenges posed by the invasion of the blue crab in the Mediterranean Sea.