Strait of Hormuz Standoff Creates Underwater Bioinvasion Risk for 1,500 Stranded Ships

Nearly 1,500 ships have been sitting idle in the Persian Gulf for close to five months, trapped since fighting between the US and Iran shut down movement through the Strait of Hormuz on February 28, 2026. Marine scientists now say the real danger from this standoff may not be on these ships at all, it could be growing right beneath them.

A new study in the journal Biological Invasions warns that the hulls of these stranded vessels have turned into breeding grounds for barnacles, mussels, algae and other sea creatures. Led by 24 scientists from the University of Maryland Center for Environmental Science and the Woods Hole Oceanographic Institution, the research says this build-up could trigger what it calls a "bioinvasion super-spreader event" the moment the ships finally start moving again.

The Strait of Hormuz isn't just any stretch of water. It's the only open-sea exit for oil giants like Saudi Arabia, Iran, Iraq, Kuwait and the UAE, and it usually carries around $600 billion worth of energy trade every year. Since the war began, roughly 1,500 vessels have been stuck inside the Persian Gulf, with several hundred more waiting it out in the neighbouring Gulf of Oman.

Ships that stay parked in one spot don't stay clean for long. Scientists call the build-up "biofouling", a process that starts with a thin film of slime and microorganisms, then thickens into algae, barnacles, mussels and small crustaceans clinging to the hull. The International Maritime Organization says any ship idle for more than 30 days needs urgent hull-cleaning attention. These ships have been sitting for nearly four months, right through the season when marine life grows and breeds the fastest.

Carolyn Tepolt, a biologist at Woods Hole who studies how invasive sea life spreads, points out just how hard these hitchhikers are to get rid of once they settle down. As she put it, "Marine invasive species have profound ecological and economic impacts on coastlines across the globe".

A dirty hull doesn't just carry unwanted guests, it also drags. Research cited by the IMO shows that even a thin layer of slime can push up a ship's emissions by 20 to 25 percent. Add a light coating of barnacles, and fuel use can jump by more than 50 percent. Across the shipping industry, roughly one-tenth of all fuel burned is simply spent fighting this drag.

This isn't a hypothetical worry. The Asian green mussel, native to the warm waters of the Indian and Pacific oceans and common in the Gulf, has already hitched rides on ship hulls to the Caribbean and the South Atlantic, pushing out local mussel species wherever it lands. Clam and worm species have made similar journeys before, damaging port infrastructure and displacing native life in the Atlantic and Pacific.

Ports across the Gulf aren't waiting around. Divers are being sent underwater to scrape hulls and propellers clean before ships are allowed to sail out. It isn't cheap, cleaning a single vessel now costs close to $8,000, a jump of nearly 60 percent, as shipping operators scramble to get their fleets moving again.

The episode has also rattled the insurance world. Justus Heinrich, who heads marine underwriting at Allianz, says the industry always treated chokepoint disasters as something on paper. Now, in his words, "theoretical risks have turned into practical risks."

The study's authors aren't just sounding an alarm, they're pushing for action. They want shipping companies, port authorities and regulators to tighten hull-cleaning rules, watch high-risk ports more closely, track vessel movements better and coordinate a rapid response once ships start sailing out. Their strongest recommendation: clean the hulls before departure, not after arrival. Once an invasive species sets up shop on a new coastline, the study notes, it is nearly impossible to remove.

For now, the world's busiest oil route remains jammed, and somewhere beneath all those anchored hulls, an entirely different kind of traffic is quietly building up, waiting for its own chance to set sail.