WorldShips stalled in the Gulf region due to the blockade of the Strait of Hormuz could pose an 'immense' threat, according to a paper published last week. Experts say biofouling on hundreds of ships over several months could lead to the spread of invasive species.'Worst-case scenario' as idle vessels may carry invasive species worldwideMitchell Fox · CBC News · Posted: Aug 02, 2026 4:00 AM EDT | Last Updated: August 2Listen to this articleEstimated 5 minutesThe audio version of this article is generated by AI-based technology. Mispronunciations can occur. We are working with our partners to continually review and improve the results.Tankers and cargo vessels are seen in the Gulf of Oman, along shipping routes linking the Strait of Hormuz and the Arabian Sea, Tuesday, June 16, 2026. (The Associated Press)Ships stalled in the Gulf region because of the closure of the Strait of Hormuz could trigger a "super-spreader" event, with long-term environmental consequences, according to a paper published last week.The paper, published July 22 in Biological Invasions, warns that algae, barnacles, tunicates and other organisms growing on stationary vessels in the Persian Gulf and the Gulf of Oman could pose an "immense international biosecurity threat" once the ships resume travelling."If you had to design a biofoulic spreader event and you really wanted to get as many species moved around as possible, this would be it," said lead author Mario Tamburri, a professor at the University of Maryland Center for Environmental Science.The Strait of Hormuz lies between the Persian Gulf and the Gulf of Oman. There are over 1,500 ships stalled due to the closure of the Strait as a part of the U.S.-Iran war, researchers estimate. (The National/CBC)The researchers estimate about 1,500 ships are stalled in the Persian Gulf and hundreds more in the Gulf of Oman because of the strait's closure amid the U.S.-Iran war. Biofouling — the accumulation of organisms on ships hulls, propellers and other external surfaces — could allow invasive species to spread to ports around the world if the vessels are not properly managed, the paper says.Why the ships could become 'super-spreaders'Tamburri and his co-authors describe the closure as a "worst-case scenario."Ships generally remain in port for one to three days and may go years between hull cleanings. Some vessels in the Gulf have been stationary for at least 40 times as long as usual, the researchers said.Hull coatings designed to prevent biofouling also become less effective when ships remain idle, Tamburri said.WATCH | Canadian ships stuck in Strait for months:2 Canadian freight ships stuck in Strait of Hormuz for monthsJuly 16|Duration 5:48Pascal Larose is the vice-president of Desgagnés, a shipping company that has had two vessels stuck in the Strait of Hormuz since hostilities between the U.S., Israel and Iran broke out. Larose says it's uncertain when the ships will be able to complete their voyages.The number and size of the vessels, their proximity to one another and the timing of the closure increase the risk of a "super-spreader" situation, Tamburri said. The ships became stranded as waters were warming and many organisms were beginning their growing and reproductive seasons.Species that tolerate the Persian Gulf's high temperatures and salinity may also be effective invaders elsewhere, particularly as ocean temperatures rise, Tamburri said.Cleaning the vessels before they leave would be difficult. In-water cleaning companies are not equipped to handle so many ships in a short time period, he said, and sending workers into the water during a conflict would pose safety risks. "Ideally they would all clean before they left, but most of these ships are just going to have to leave," he said.Shipping's ecological issueSpecies can move between ecosystems through cargo and ballast water, but researchers say biofouling has received less attention. After zebra mussels appeared in the Great Lakes in the mid-1980s, governments and the shipping industry focused on species transported in ballast water, said Meghan Mathieson, director of strategy and engagement for ClearSeas, a non-profit aiming to raise awareness about marine shipping. "There just was less awareness of the fact that organisms can cling to the outside of a ship and then drop off in new systems," she said.The N.W.T. will be getting a boat washing station similar to this one installed next spring. It's part of an effort to stop invasive species like zebra mussels from entering the territory. ( Invasive Species Centre)This zebra mussel was one of 19 pulled off the Mactaquac Dam by Bruce's team during last year's survey of the Saint John River. (Submitted by Meghann Bruce)Organisms can detach or release larvae when a ship reaches another port. If they become established, they may out-compete native species.Tunicates, or sea squirts, are one example. The slimy invertebrates, which spread through biofouling and ballast water, compete with mussels on farms along Canada's East Coast. The International Marine Organization released an updated set of guidelines around biofouling in 2023. Unlike for ballast treatment, Mathieson said there are no mandatory regulations yet but they are in the works.WATCH | East coast shellfish face tunicate invasion:Slimy and spreading fast: Shellfish farms face biofouling 'invasion'June 26, 2023|Duration 3:02Scientists are monitoring dozens of sites in Nova Scotia and southern New Brunswick to see if the latest warm winter in Atlantic Canada accelerated the spread of slimy biofouling marine invertebrates. Paul Withers has the story.Such species are nearly impossible to eliminate once established, said Anthony Ricciardi, a biology professor and director of McGill University's Bieler School of the Environment."There's a chronic cost to having an invasion once it's entrenched," he said.Ecological invasionRicciardi compared marine invasions to a hub-and-spoke network: Ships carry organisms to ports, that may become new hubs for further spread. With so many vessels stalled in the Gulf, he said, they are likely to collect an "abundance and diversity" of organisms, increasing the risk of invasions elsewhere. The situation shows how geopolitical events can have ecological consequences far beyond the region where they occur, he said.The scale and impact of any spread remain unknown."What happens in the Strait of Hormuz will probably fuel a legacy that will keep unfolding," Ricciardi said. "You have to look at it as not just a one-off, but as a major step change in the marine invasion risk worldwide, at least in areas that can accommodate these particular species."ABOUT THE AUTHORMitchell Fox is a summer intern with CBC News' climate/science unit. Born and raised in Mississauga, Ont., he is currently finishing his master's degree at Western University. He can be reached at mitchell.fox@cbc.ca