More than 1,500 commercial vessels have been stranded in the Gulf since the Strait of Hormuz closed on 28 February after the outbreak of the US-Israel war on Iran. Scientists warn that the prolonged idling has allowed marine life to encrust hulls, creating a potential "super-spreader" event for invasive species when ships resume sailing.
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." Normally, ships remain anchored for only one to three days, limiting organism growth. But many vessels have been stationary for months, allowing dense communities of microbes, algae, barnacles, and other invertebrates to establish on their hulls.
"If you had to design the worst-case scenario, I don't know if you could have done it differently," Tamburri said. The research calls it a potential marine "bio-invasion super-spreader event," noting no previous shipping disruption involved so many idle vessels for so long.
Risks to Ecosystems and Economies
When thousands of ships leave, they could carry hitchhiking organisms that outcompete native wildlife, spread disease, and alter marine ecosystems. "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 power plant cooling systems, and cost billions of dollars annually to manage.
Gulf's Extreme Conditions May Harden Invaders
The Gulf is already a hotspot for marine invasions, with dozens of non-native species introduced by shipping. The region's extreme heat and salinity may make the organisms especially resilient. "They're pretty hardy," Tamburri said. "Those hardy organisms that can often withstand those extreme environments make really good invaders."
Ports with similar warm, salty conditions face the highest risk. Tamburri highlighted India and Singapore as locations where authorities should be on alert.
Call to Action
The study warns that individual ships may have already released millions of larvae into Gulf waters. As shipping resumes, organisms in ballast water and biofouling communities could spread rapidly. Tamburri urged governments and shipping companies to inspect and clean ships before departure, and ports to increase monitoring and establish rapid-response plans.
"Early detection is really important – prevention before you move around is really important," he said, comparing the response to tracking infectious diseases like flu or Covid.
A spokesperson from the International Maritime Organization said: "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 minimise the transfer of invasive aquatic species."
Potential Lasting Damage
Referring to ecosystems such as coral reefs, seagrass meadows, and oyster beds, Tamburri said: "If authorities fail to act, some of the world's most valuable marine habitats could suffer lasting damage." He called it a "super-spreader version" of how ships already transport invasive species.
While human safety remains the priority, Tamburri urged governments not to ignore environmental risks. "Conflicts like this are horrible," he said. "There's human suffering, but we can't ignore the environmental consequences, either."
