The spread of Indo-Pacific origin fish species in the Mediterranean Sea is influenced by sea currents, habitat factors, and increasingly by shipping

The construction of the Suez Canal initiated a profound marine biogeographic rearrangement by connecting two marine regions that had been separated for about 16 million years. To date, more than 100 fish species native to the Indo-West Pacific Ocean have crossed the Suez Canal and become established in the Mediterranean Sea. The purpose of this study is to identify the major factors that influence how fish species of Indo-Pacific origin (FSIPO) spread within the Mediterranean. We analyzed Mediterranean records of 136 FSIPOs, divided the Mediterranean Sea into polygons, and examined how sea currents, shipping, environmental variables, and species characteristics affect the probability that an FSIPO record is found in a polygon. Our analysis showed that any particular FSIPO is more likely to colonize regions that receive currents from the entrance of the Suez Canal, as well as regions that are close to – or receive currents or cargo ships from – other regions already occupied by the same species. Higher salinity is linked to increased colonization rates, and colonization rates overall show a significant increase over time. In addition, colonization due to spatial proximity to occupied regions and due to shipping increased significantly over time. Comparisons between simulated and observed rates of spread showed that there is additional variation among fish species that our analysis did not capture.