Thousands of idle ships near the Strait of Hormuz could become floating nurseries for invasive marine species, spreading them around the world when trade resumes

(Representative image) Image source: Getty Images

The current war between the United States and Iran has lasted nearly five months since it escalated into open hostilities on February 28, 2026. During this period, the Strait of Hormuz, the only high-seas outlet for major oil producers including Saudi Arabia, Iran, Iraq, Kuwait and the United Arab Emirates, has been blocked. The strait is the world’s most important maritime energy chokepoint, facilitating approximately $600 billion worth of energy trade each year. It is estimated that around 1,500 ships are stuck in the Persian Gulf, with hundreds more in the neighboring Gulf of Oman.Now, according to new research, what grows on these hulls may spread around the world when trade resumes. The study, published in Biological Invasions, was led by an international team of 24 marine scientists led by the University of Maryland Center for Environmental Sciences (UMCES) and including the Woods Hole Oceanographic Institution (WHOI).Thousands of commercial ships stranded in the Persian/Arabian Gulf for months following the closure of the Strait of Hormuz could inadvertently trigger large-scale marine invasive species incidents, a research team warns. The study, “Closing the Strait of Hormuz may trigger a biological invasion super-spreader event,” highlights how long periods of anchorage allow ships to accumulate dense communities of marine life, including algae, barnacles, mussels and other invertebrates, which can be transported around the globe when trade resumes.

“Super spreader” event

This phenomenon is known in the maritime industry as “biofouling,” the accumulation of marine life on underwater surfaces such as ship hulls and propellers. It starts with a thin layer of microorganisms and slime, then develops into algae, barnacles, small marine crustaceans and shelled organisms.The authors describe the unprecedented idling of more than 1,500 ships, creating conditions for a potential global “super-spreader” event of marine life invasion. WHOI biologist Carolyn Tepolt, whose research focuses on the evolution and spread of marine invasive species, contributes expertise on how globally distributed biofouling organisms rapidly adapt to new environmental conditions.“Marine invasive species have profound ecological and economic impacts on coastlines around the world, and once they become established, they are difficult to eradicate,” Tebolt explained. The disruption to global shipping had many impacts and quietly created ideal conditions for the spread of warm-water species to new ports. “

imminent threat

The International Maritime Organization recommends that ships idle for more than 30 days require immediate intervention to manage biofouling before sailing, but these ships have been stranded for nearly four months during the peak period of marine life growth and reproduction. According to research cited by the International Maritime Organization (IMO), even a thin layer of slime can increase greenhouse gas emissions by 20-25%, while slight barnacle growth can increase fuel consumption and emissions by more than 50%. The IMO estimates that approximately 10% of the shipping industry’s fuel consumption is used to overcome resistance related to biofouling.The authors also note that modern shipping has long been recognized as a major conduit for invasive species in the ocean. They also warned that the scale and duration of recent ship layups are unlike anything previously recorded, creating an unprecedented but daunting global biosecurity challenge. In recent decades, invasive species have wreaked havoc in multiple regions around the world through the spread of biofouling, including from the Gulf. During one of these spreads, clam and worm species spread across the Atlantic and Pacific Oceans, displacing native species and damaging port infrastructure.Biofouling also affects the resistance a ship experiences as it moves through the water, impairing the ship’s ability to move. As a result, ships are forced to consume additional energy, leading to increased use of polluting fuels. One of the striking examples of ecological impacts is the Asian green mussel, which is considered a particularly aggressive invasive species. Originating in tropical areas of the Indian and Pacific Oceans and also common in the Gulf, the mussel has spread to the Caribbean and South Atlantic, displacing native mussel species and causing ecological damage.The group calls on ship operators, port authorities, regulators and environmental managers to strengthen ship biofouling management, expand monitoring of high-risk ports, improve predictions of ship movements and coordinate international rapid response efforts. According to the authors, “in-water cleaning” of ships to remove biofouling before departure can be very effective in mitigating the risk of their invasion.According to recent reports, divers were deployed at Gulf ports to scrape the hull and propeller of the ship before it could resume commercial operations. As operators move out of the bay, the cost of cleaning a single vessel could increase by as much as 60%, to about $8,000 per vessel.Justus Heinrich, head of marine underwriting at Allianz, said the incident had revolutionized the way the business world viewed risks associated with choke points. “It used to be realistic disaster scenarios. But now, we’re seeing real disaster scenarios, which means the theoretical risk has turned into a real risk.”

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biofoulingecological disasterglobal trade impactInternational Maritime OrganizationInvasive marine speciesmarine biodiversitymarine ecosystemshipping industryStrait of HormuzUniversity of Maryland Environmental Science Center