Ships stranded in Strait of Hormuz could trigger biological invasions

More than 1,500 large commercial vessels stranded in the Strait of Hormuz following its closure amid tensions between the US and Iran could trigger a global wave of biological invasions, researchers have warned.

A study published in the journal "Biological Invasions" says marine organisms accumulating on ship hulls during extended stationary periods may be transported to ports worldwide once traffic resumes, potentially creating a "super-spreader" effect for invasive species.

The study found that biofouling, consisting of marine microorganisms, algae, and invertebrates, can rapidly develop on the hulls of ships that remain stationary for extended periods.

According to the study, more than 1,500 large commercial vessels have becomes stranded following the closure of the Strait of Hormuz on February 28, 2026.

The prolonged presence of these ships in the region allows local organisms to colonize their hulls, while also bringing together communities of organisms from different parts of the world on the same vessels.

Professor Mario Tamburri of the University of Maryland, the study's lead author, described the current situation as a "worst-case scenario" compared to previous shipping disruptions.

The risk is amplified by several converging factors: the unprecedented number and size of stranded vessels, combined with the fact that the closure coincides with spring and summer—peak seasons for marine organism growth and reproduction.

Organisms native to the Gulf, already adapted to extreme temperatures and high salinity, may prove particularly resilient when introduced to new environments.

Tamburri said the length of time a vessel remains stationary is critical in determining the amount and diversity of biofouling.

“The longer they remain stationary during periods of productive growth and reproduction, the more extensive and diverse the biofouling on the ships becomes,” he said.

The study stresses that vessels in the Gulf have remained stationary far longer than normal port waiting periods, creating favorable conditions for invasive species to reproduce on their hulls and be transported to other regions.

Tamburri said it is difficult to predict with certainty which species will be spread by ships, as the risk depends on numerous variables involving both the species and the environmental conditions to which they are transported.

The study also notes that species transported through biofouling can affect not only ecosystems but also economic activities, while certain parasites and pathogens may threaten commercially important species.

The study emphasizes that the first ports visited by ships departing the Strait of Hormuz are particularly important for the establishment of invasive species.

The researchers recommend cleaning the biofouling from ships’ hulls before they leave the Gulf as the ideal solution.

However, they note that applying this measure to every vessel would be difficult because the region has limited capacity for such operations and ships may need to leave quickly for security, logistical, and operational reasons.

The study identifies specific ports facing elevated invasion risks due to short voyage times and similar environmental conditions. Jeddah, Mumbai, Colombo, Singapore, Alexandria, Piraeus, Algeciras, and Rotterdam are highlighted as particularly vulnerable first destinations.

The Asian green mussel, native to the Gulf, serves as a cautionary example—having already established itself in Florida, the Caribbean, Australia, and South America, where it competes with native species and clogs industrial infrastructure.

Researchers warn that the international maritime community remains ill-prepared for this biosecurity threat. While regulations are being developed through the International Maritime Organization (IMO), they will take years to finalize.

The study recommends implementing early-warning and rapid-response systems at first ports of call, alongside coordinated international efforts bridging biological invasion science, maritime logistics, and regulation.