Nearly 1,500 ships have been stranded in the Persian Gulf for close to five months, immobilised since the outbreak of hostilities between the United States and Iran forced the closure of the Strait of Hormuz on 28 February 2026, Economic Times reported.
While the geopolitical standoff has dominated headlines, marine scientists warn that the greater danger may be unfolding beneath the surface of the water rather than on the decks of these vessels.
A new study published in the journal Biological Invasions highlights that the hulls of these idle ships have become breeding grounds for barnacles, mussels, algae and other marine organisms.
The research, led by 24 scientists from the University of Maryland Center for Environmental Science and the Woods Hole Oceanographic Institution, warns that this accumulation could trigger what they describe as a “bio-invasion super-spreader event” once the ships resume movement.
The Strait of Hormuz is not just another maritime passage. It is the sole open-sea exit for oil-exporting nations such as Saudi Arabia, Iran, Iraq, Kuwait and the United Arab Emirates.
Ordinarily, it carries around $600 billion worth of energy trade annually. Since the war began, approximately 1,500 vessels have been trapped in the Persian Gulf, with several hundred more waiting in the Gulf of Oman.
Ships that remain stationary for extended periods quickly accumulate marine growth. Scientists refer to this process as “biofouling”, which begins with a thin microbial film and progresses into algae, barnacles, mussels and crustaceans clinging to the hull.
The International Maritime Organization stipulates that any vessel idle for more than 30 days requires urgent hull-cleaning. These ships have now been stationary for nearly four months, coinciding with peak breeding season for marine life.
Carolyn Tepolt, a biologist at Woods Hole, emphasises the resilience of these organisms once they establish themselves. She notes that marine invasive species can have profound ecological and economic consequences for coastlines worldwide, making them extremely difficult to eradicate once introduced.
The implications extend beyond ecology. A fouled hull increases drag, forcing ships to burn more fuel. Research cited by the IMO shows that even a thin slime layer can raise emissions by 20 to 25 percent.
A light coating of barnacles can increase fuel consumption by more than 50 percent. Across the global shipping industry, roughly one-tenth of all fuel burned is wasted combating this drag.
This is not a theoretical risk. The Asian green mussel, native to the Indian and Pacific oceans and common in the Gulf, has already spread to the Caribbean and South Atlantic via ship hulls, displacing local species. Other invasive clams and worms have similarly travelled across oceans, damaging port infrastructure and disrupting native ecosystems.
Ports across the Gulf are already deploying divers to scrape hulls and propellers before ships are permitted to sail. The cost of cleaning a single vessel has surged to nearly $8,000, an increase of about 60 percent, as operators rush to prepare their fleets for eventual departure.
The insurance industry has also been shaken. Justus Heinrich, head of marine underwriting at Allianz, remarked that chokepoint disasters were once considered theoretical risks. Now, he says, they have become practical realities.
The study’s authors are urging immediate action. They recommend stricter hull-cleaning regulations, closer monitoring of high-risk ports, improved vessel tracking and coordinated rapid responses once ships begin moving again. Their strongest advice is to clean hulls before departure rather than after arrival, as invasive species are almost impossible to eliminate once they colonise a new coastline.
For now, the world’s busiest oil route remains paralysed. Beneath the anchored ships, however, a silent build-up of marine life continues, preparing for what could become the largest bio-invasion event in history once the blockade ends.
Agencies
