More than 1,500 commercial vessels have been stranded in the Gulf of Oman since the Strait of Hormuz closed on 28 February following the outbreak of the US-Israel war on Iran, creating conditions for an extreme global biodiversity threat, scientists have warned. An international team of marine biologists said the prolonged idling has allowed dense marine communities to encrust ship hulls, potentially turning these vessels into vectors for invasive species once trade resumes.
Perfect storm for bio-invasion
Prof Mario Tamburri, of the University of Maryland Center for Environmental Science and lead author of the study, described the situation as a perfect storm. “If you had to design the worst-case scenario, I don’t know if you could have done it differently,” he said. The research, which characterizes the event as a potential marine “bio-invasion super-spreader event,” notes that no previous shipping disruption has involved so many vessels remaining idle for such an extended period.
Ships normally anchor for only one to three days in a harbour, limiting the growth of organisms on their submerged surfaces. However, many trapped vessels have remained stationary for months, allowing communities of microbes, algae, barnacles, and other invertebrates to establish themselves. When these ships eventually depart, they could carry these organisms to ports worldwide.
Ecological and economic risks
“When you move organisms around, they can reduce biodiversity in the regions they invade, cause local extinction of organisms that they displace,” Tamburri said. Invasive species can also devastate fisheries, clog the cooling systems of power plants, and cost billions of dollars annually to manage. The Gulf region is already a hotspot for marine invasions, with previous studies identifying dozens of non-native species introduced largely by commercial shipping.
The extreme heat and salinity of the Gulf may make the organisms especially resilient. “They’re pretty hardy. They’re used to extreme environments, high temperatures and high salinities,” Tamburri said. “Those hardy organisms that can often withstand those extreme environments make really good invaders.” He highlighted India and Singapore as locations where authorities should be on high alert due to similar warm, salty conditions.
Urgent calls for preventive action
The study warns that individual ships may have already released millions of larvae into Gulf waters during the months-long lay-up. As shipping resumes, organisms in ballast water, as well as parasites and pathogens in biofouling communities on hulls, could spread rapidly through the global shipping network. Tamburri urged governments and shipping companies to inspect and clean ships before they leave the Gulf wherever possible, while ports expecting arrivals should increase monitoring for invasive species and establish rapid-response plans.
Drawing a comparison with public health, Tamburri said the response should mirror efforts to contain infectious diseases. “Early detection is really important – prevention before you move around is really important. In a lot of ways, it is like tracking flu or Covid. You want to be prepared for it, detect it early. If you find something, manage it right away.”
International response and future risks
A spokesperson from the International Maritime Organization (IMO) acknowledged the risk: “Biofouling can be a key vector for transfer of invasive aquatic species. There is a risk of transfer of species if ships are unable to remove fouling before moving out of an area, after a prolonged period of time in one area. The IMO recommends that ship operators follow the IMO biofouling guidelines as far as possible.” The IMO is currently developing a standalone legally binding instrument for the control and management of ships’ biofouling to minimize the transfer of invasive aquatic species.
Tamburri warned that without action, some of the world’s most valuable marine habitats—such as coral reefs, seagrass meadows, and oyster beds—could suffer lasting damage. “Some of those are likely to be impacted and perhaps damaged beyond repair,” he said, calling it a “super-spreader version” of the way ships already transport invasive species globally. While human safety remains the priority, he urged governments not to ignore the environmental risks. “Conflicts like this are horrible. There’s human suffering, but we can’t ignore the environmental consequences, either.”
