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More than 1,500 commercial ships stranded in the Persian Gulf could unintentionally trigger a global ecological crisis by transporting invasive marine species to coastlines around the world once shipping resumes, according to a new international study.
The vessels have remained anchored in the Persian Gulf and Gulf of Oman for months, allowing algae, barnacles, mussels, microbes, and other marine organisms to accumulate on their submerged hulls. Scientists say this prolonged inactivity has transformed the ships into floating ecosystems capable of carrying invasive species across international shipping routes.
The study was led by researchers at the University of Maryland Center for Environmental Science, with contributions from scientists at the Woods Hole Oceanographic Institution and other international institutions. They describe the unprecedented shipping disruption as a potential marine bioinvasion “super-spreader” event.
Ships routinely transport marine life through ballast water and organisms attached to their hulls. However, commercial vessels typically remain in port for only one to three days. In contrast, many of the stranded ships have been stationary for weeks or months, giving marine organisms ample time to settle, reproduce, and spread. Biofouling can begin growing rapidly after about 10 days on an idle vessel, while antifouling coatings become less effective when ships are not moving.
Researchers note that the Persian Gulf provides ideal conditions for marine growth due to its shallow waters, high salinity, and extreme summer temperatures, which can approach 100 degrees Fahrenheit (38 degrees Celsius). Previous surveys have already documented dozens of nonnative species thriving in ports throughout the region.
The threat extends beyond visible marine growth. Biofouling communities can transport parasites and pathogens that infect native wildlife and commercially important fisheries. Scientists also warn that mixing genetically distinct populations may produce more resilient invasive species capable of adapting to warming oceans.
The researchers examined shipping records from more than 3,000 vessels connected to over 3,500 ports worldwide, highlighting how quickly organisms could spread once trade resumes. While cleaning ships before departure would provide the best protection, limited regional capacity and the urgency of restoring shipping operations may make that difficult.
Instead, the team recommends inspecting vessels for biofouling before departure, identifying their destinations, and alerting receiving ports to reduce the risk of a worldwide marine invasion.
