In 1869, the construction of the Suez Canal was completed, connecting two marine regions previously separated for 16 million years and initiating major ecological changes that continue to this day.
Now more than 100 fish species native to the Indo-West Pacific Ocean – including the ‘devil firefish’ – have crossed to become established in the Mediterranean Sea.
But how do they make the journey?
Researchers from the American University of Beirut and the American University in Dubai analysed how invasive fish from the Indo-Pacific region colonise the Mediterranean. Combining ocean current modelling, shipping data, and environmental analysis, they examined records of 136 fish species to map the natural and human-driven factors that enable these invaders to thrive.
Published in NeoBiota, the findings indicate that the primary drivers for the initial entry of invasive fish into the Mediterranean are proximity to the Suez Canal and sea currents transporting fish larvae into nearby eastern Mediterranean regions. However, while sea currents play an important role early in the invasion stage, they cannot explain how species cross into the western Mediterranean.
Indeed, cargo shipping has become increasingly influential, with focal points like Malta acting as key stepping stones for the spread of non-native fish, especially to western Mediterranean areas. Over time, the odds of a region being colonised via shipping have grown significantly.
Additionally, local conditions such as high salinity in Mediterranean waters boost the likelihood of invasive species establishing permanent populations, as these fish tend to be pre-adapted to saline environments from their native habitats.
“Scientists have long suspected that the anti-clockwise spread of invasive species in the eastern Mediterranean is due to currents and the high number of first records in Malta is due to shipping.
“Our use of sea current simulations and shipping data could confirm these conjectures and provide quantitative estimates of the effects.”
Heinrich zu Dohna, lead author of the paper.
Logistic regression models indicate that in some regions shipping leads to a sixfold increase of the odds of receiving invasive species, indicating targeted management and monitoring is needed at major shipping hubs.
Better data on ballast water release and ship movements in the Mediterranean are needed, as cargo shipping’s impact on biological invasions is now clear. Malta’s role as a major shipping hub makes it a particular hotspot for secondary introductions and warrants special attention by policymakers and marine managers.
Original source
zu Dohna H, Lakkis I, Bariche M (2025) The spread of Indo-Pacific origin fish species in the Mediterranean Sea is influenced by sea currents, habitat factors, and increasingly by shipping. NeoBiota 101: 73-89. https://doi.org/10.3897/neobiota.101.157775