Ballast water-mediated species spread risk dynamics and policy implications to reduce the invasion risk to the Mediterranean Sea

This study helps understand the ballast water-mediated species spread risk dynamics in the Mediterranean and examine potential policy options for ballast water management to further reduce species spread risk in the region. Results show that Gibraltar, Suez, and Istanbul remained high-risk ports from 2012 to 2018, and they are hub ports connecting several clusters. We reveal ballast water management implications for both the Mediterranean region and individual hub ports respectively. To further reduce the risks of individual Mediterranean hub ports beyond the IMO standards, the most effective (cost-effective) regulatory method is to set more stringent regulation towards such hub ports besides the IMO regulation. To further reduce the risks of the Mediterranean as a whole, the most effective (cost-effective) regulatory scenario is to set more stringent regulation towards all Mediterranean ports besides the IMO regulation. The barge-based method is the most cost-effective technology to achieve stricter regulations. •Gibraltar, Suez, Istanbul, and Algeciras remain high-risk ports from 2012 to 2018.•High-risk ports connect most different risk spread clusters.•An additional regional stricter regulation is cost-effective for hub ports.•An additional regional stricter regulation is cost-effective for the Mediterranean.