Strait of Hormuz ship standstill could trigger global marine invasive species crisis, warn scientists

Nearly five months after the United States-Iran conflict escalated into open hostilities on February 28, 2026, scientists are warning of an unexpected environmental consequence of the prolonged disruption to global shipping.

With the Strait of Hormuz effectively closed, more than 1,500 commercial vessels have remained stranded in the Persian Gulf, while hundreds more are waiting in the neighbouring Gulf of Oman. Beyond disrupting one of the world's busiest energy corridors, researchers say the prolonged lay-up of these ships could unleash a worldwide marine invasive species event once normal shipping resumes.

The warning comes from a study published in the journal Biological Invasions by an international team of 24 marine scientists led by the University of Maryland Center for Environmental Science (UMCES), with contributions from the Woods Hole Oceanographic Institution (WHOI).

The researchers say months of inactivity have allowed dense layers of marine organisms to accumulate on ship hulls, a process known as biofouling. The buildup begins with microscopic bacteria and slime before expanding into algae, barnacles, mussels, worms and other invertebrates. Once ships leave the Gulf, these organisms could be transported to ports around the world, where they may establish themselves as invasive species.

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The study describes the unprecedented concentration of idle vessels as a potential global marine "super-spreader" event.

"Marine invasive species have profound ecological and economic impacts on coastlines across the globe and are extremely difficult, if not impossible, to eradicate once they become established," said Carolyn Tepolt, a WHOI biologist and co-author of the study. She noted that the shipping disruption has quietly created ideal conditions for warm-water species from the Gulf to spread into new ecosystems.

The International Maritime Organization (IMO) recommends that vessels remaining idle for more than 30 days undergo biofouling management before sailing. However, many of the stranded ships have remained stationary for nearly five months, coinciding with the peak growth and reproduction season for many marine organisms.

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Apart from ecological risks, biofouling also reduces a vessel's efficiency. Even a thin layer of slime can increase greenhouse gas emissions by 20-25%, while light barnacle growth can raise fuel consumption and emissions by more than 50%, according to IMO estimates. The organisation estimates that about 10% of the global shipping industry's fuel use is spent overcoming the additional drag caused by biofouling.

Scientists point to past examples showing how invasive species transported by ships have damaged marine ecosystems and coastal infrastructure. One notable case is the Asian green mussel, native to the Indian and Pacific oceans and common in Gulf waters, which has spread to the Caribbean and South Atlantic, displacing native species and disrupting local ecosystems.

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To reduce the risk, the researchers are urging ship operators, port authorities and regulators to strengthen biofouling management, expand monitoring at high-risk ports and coordinate international response measures. They say in-water cleaning of hulls before ships depart could significantly reduce the likelihood of invasive species spreading.

Reports indicate that divers have already begun cleaning ship hulls and propellers across Gulf ports. The cost of cleaning a single vessel could rise to nearly $8,000 as operators prepare to resume commercial operations.

While attention has largely focused on the economic and geopolitical fallout of the conflict, researchers warn that one of its most lasting consequences may be an invisible ecological threat carried across oceans on the hulls of stranded ships.

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