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

TL;DR

This study assesses ballast water-mediated species invasion risks in the Mediterranean, identifying key ports and evaluating policy scenarios to effectively reduce invasion risks through targeted regulations.

Contribution

It provides a detailed risk analysis of port connectivity and evaluates the effectiveness of different regulatory strategies for invasive species management.

Findings

High-risk ports like Gibraltar, Suez, and Istanbul are key spread hubs.

Regulating high-risk hub ports significantly reduces overall invasion risk.

Targeted regulation of high-risk ports is more effective than broad policies.

Abstract

The Mediterranean Sea is one of the most heavily invaded marine regions. This work focuses on the dynamics and potential policy options for ballast water-mediated nonindigenous species to the Mediterranean. Specifically, we (1) estimated port risks in years 2012, 2015, and 2018, (2) identified hub ports that connect many clusters, and (3) evaluated four regulatory scenarios. The risk results show that Gibraltar, Suez, and Istanbul remained high-risk ports from 2012-2018, and they served as hub ports that connected several spread clusters. With policy scenario analysis, we found that regulating the high-risk hub ports can disproportionately reduce the overall risk to the Mediterranean: the average risk to all ports was reduced by 5-10% by regulating one high-risk hub port, while the average risk to all ports was only reduced by 0.2% by regulating one average-risk Mediterranean port. We also found that only regulating high-risk ports cannot reduce their risks effectively.