Ships idled in the Strait of Hormuz region since February have created conditions for extensive hull biofouling, according to recent research identifying more than 1,500 commercial vessels laid up in the Persian/Arabian Gulf. When these vessels resume transit, they will carry organisms attached to hulls and niche areas that can be translocated to distant ports and coastal environments.
Accumulated biofouling includes marine plants, invertebrates, parasites and pathogens that can establish as non-native species in new regions, with documented impacts on native ecosystems, fisheries and aquaculture. The Gulf region is already host to more than 50 documented marine non-native species, and prolonged vessel layups increase the likelihood of transporting organisms beyond historical distribution ranges. Research highlights the potential for large-scale, multi-port spread when many vessels depart a constrained area.
Maritime analyses identify 24 global choke points in merchant shipping, with only four lacking practicable alternatives: the Strait of Hormuz, the Oresund, the Bosporus and Dardanelles, and the Bohai Strait. Historical and economic factors have previously produced mass layups—examples include wide vessel idling during the 2008 financial crisis and earlier oil-market disruptions—demonstrating that shipping interruptions can rapidly create biofouling challenges when large numbers of vessels remain stationary.
Implications for distant biosecurity jurisdictions are tangible. While immediate arrivals of large numbers of Gulf-laid-up vessels to locations such as New Zealand and Australia are unlikely in the first weeks after reopening, modelling and observational data indicate a substantial increase in risk within months. Both countries maintain established regulatory frameworks and response capacity; for example, Biosecurity New Zealand implemented screening and remedial actions for cruise ships during the COVID-19 pandemic.
To reduce translocation risk, coordinated measures recommended by researchers include pre-departure inspection and assessment, targeted in-water cleaning that captures removed material, forecasting and notification of first-port destinations, and deployment of environmental DNA and rapid assessment tools by receiving ports to enable early detection and rapid response. International cooperation and timely information sharing between flag states, port authorities and national agencies are central to managing the documented biosecurity threat posed by vessels leaving the Strait of Hormuz region.
