Temporal trends of the bioinvasion risk through ballast water: a case study in the Maranhão harbor (Brazil)

The last two decades were marked by many attempts in addressing the risk of bioinvasion through ballast water and biofouling on ships’ hulls and surfaces. In Brazil, there is also an increasing concern about the risk of bioinvasion, mainly in the Amazon Basin and the coastal adjacent areas that can trigger a secondary spread. This is the case of Maranhao, where the most active port in Brazil has doubled the gross tonnage of seaborne freight during the last ten years (2010–2019). To check for a potential rise in the biological risk at the Maranhao harbor over the last ten years due to the increase in freight, this study performed a semi-quantitative risk assessment approach based on a modified GloBallast Risk Assessment Analysis. The volume and frequency of ballast water delivered in 2010 and 2019 were combined with the environmental similarity between Maranhao and 357 ports worldwide in a 1-degree × 1-degree grid to address the temporal and spatial change in the risk of bioinvasion as measured by the Relative Overall Risk (ROR). While in 2010 some ports in the North Sea, the Mediterranean, and the Indo-Pacific macroregions imposed higher bioinvasion risk, those from Indo-Pacific and the Arabian Sea reached a high-risk level in 2019. The risk assessment analysis was sensitive to a decadal shift in the ROR and ten regions were found to impose a higher risk to Maranhao.