Stranded Ships in the Strait of Hormuz Could Trigger Global Spread of Invasive Species
More than 1,500 commercial vessels have been stranded in the Strait of Hormuz following its closure on February 28 amid tensions between the United States and Iran, and researchers warn that the prolonged idling could turn these ships into vectors for biological invasions across the globe.
In a study published in the journal Biological Invasions, scientists led by Mario Tamburri, a professor at the University of Maryland Center for Environmental Science, and Carolyn Tepolt, an associate scientist at Woods Hole Oceanographic Institution, examined the risk posed by biofouling—the accumulation of marine organisms on submerged surfaces such as ship hulls.
Biofouling communities, which include algae, barnacles, sea squirts, and other invertebrates, can proliferate rapidly when ships remain stationary for extended periods. Ships normally rely on antifouling coatings to minimize growth, but these paints become overwhelmed when vessels sit idle for weeks or months.
A 'Worst-Case Scenario' for Bioinvasion
Tamburri described the current situation as a "worst-case scenario" compared with previous instances of ships waiting for extended periods. He pointed to several compounding factors: the sheer number and size of the vessels, the timing during spring and summer when marine organisms are actively reproducing, and the fact that organisms in the Persian Gulf are adapted to extreme heat and salinity—traits that could make them particularly resilient invaders in new environments.
A U.S. military naval blockade remains active in the strait, according to WGBH's reporting, and traffic has been massively reduced over the summer. In addition to the more than 1,500 ships trapped within the Persian Arabian Gulf, several hundred more are reported to be idle outside the strait in the Gulf of Oman.
The researchers note that in-water cleaning options exist but are not currently equipped to handle all the stranded vessels safely and effectively amid the conflict. They recommend cleaning hulls before ships depart the Gulf, but limited regional capacity, along with security, logistical, and operational constraints, may prevent that from being applied to every vessel.
High-Risk Ports and Potential Impact
Once these ships leave the region, they can reach ports worldwide, with Asia and Europe at the highest risk, followed by the Americas and Australia. The study identifies the first ports of call as particularly critical for the establishment of invasive species. High-risk ports include Jeddah, Mumbai, Colombo, Singapore, Alexandria, Piraeus, Algeciras, and Rotterdam.
Tepolt noted that organisms in the warm Gulf environment may carry genetic diversity adapted to heat, which could give recipient populations adaptive flexibility in a warming world. However, she emphasized that predicting the next invader is difficult; potential invaders range from microbes, including pathogens, to larger organisms.
The Asian green mussel serves as a cautionary example. Native to the Gulf region, it has become invasive in Florida, the Caribbean, South America, and Australia, where it clogs cooling systems at power plants and desalination facilities and has displaced native organisms.
Preparedness and Recommendations
The study urges implementing early-warning and rapid-response systems at the first ports visited by these vessels after they depart the Gulf. Tamburri told Anadolu that the international maritime community is not yet sufficiently prepared to address biosecurity risks from such prolonged, large-scale shipping disruptions. He also noted that International Maritime Organization (IMO) regulations are being developed but will take several years to be fully approved.
According to the research, biofouling can begin rapid growth within about 10 days of a ship remaining stationary. If vessels are idle for 18 to 30 days, biofouling management measures should be considered; ships stationary for more than 30 days are strongly advised to clean their hulls before the next voyage.
The scientists stress that species transported through biofouling can harm ecosystems and economic activities, and certain parasites and pathogens may threaten commercially important species. The longer the blockade persists, the greater the risk, they conclude.