Last updated: July 24, 2026

Strait of Hormuz ships today: Scientists warn of bioinvasion risk

Scientists are warning that more than 1,500 commercial vessels stranded for months in the Persian Gulf after movement through the Strait of Hormuz was shut down could carry invasive marine species around the world when shipping resumes. The concern centers on organisms such as algae, barnacles, mussels and other invertebrates accumulating on stationary hulls. Researchers say the extraordinary number of idle ships creates a biosecurity risk that could spread far beyond the Gulf, including to ports reached by vessels returning to global trade routes.

The Story at a Glance

A study published in Biological Invasions by an international team of 24 marine scientists describes the mass vessel lay-up as conditions for a potential marine bioinvasion “super-spreader” event. Ships that remain still for long periods can develop heavy biofouling, allowing organisms to attach, grow and reproduce before potentially being transported to distant ports.

The vessels have been stranded amid the closure of the Strait of Hormuz following hostilities involving the United States and Iran. Several sources place the number of ships inside the Persian Gulf at roughly 1,500, with additional vessels waiting in the Gulf of Oman.

The researchers are urging operators and authorities to assess hull fouling, clean vessels where possible before departure, forecast their first ports of call and strengthen monitoring for invasive species when normal traffic resumes.

How the Story Developed

Movement through the Strait of Hormuz was shut down on February 28, 2026, according to reports describing the regional conflict. As the disruption stretched across several months, commercial ships remained anchored far longer than they normally would.

That waiting period created a second problem beneath the waterline. Biofouling begins when microscopic organisms form a thin film on submerged surfaces. Over time, that layer can develop into algae, barnacles, mussels and other marine growth attached to hulls, propellers, sea chests and other equipment.

The concern intensified because these organisms can travel with ships once trade restarts. Researchers say modern shipping is already a major pathway for invasive marine species, but the scale and duration of this vessel backlog are unlike previously documented lay-ups.

Industry specialists also warn that fouling is not only an ecological issue. Marine growth increases drag and can restrict seawater systems, reduce vessel efficiency and increase maintenance demands. Research cited in the coverage says even a thin slime layer can increase emissions by 20% to 25%, while light barnacle growth can raise fuel consumption and emissions by more than 50%.

Biofouling

The accumulation of marine organisms on submerged surfaces such as ship hulls and propellers.

Marine bioinvasion

The spread and establishment of non-native marine species in new ecosystems.

In-water cleaning

Removing organisms from a vessel's submerged surfaces while the ship remains in the water.

Key People and Details

The research involved 24 scientists led by the University of Maryland Center for Environmental Science, with participation from the Woods Hole Oceanographic Institution. Lead author Mario Tamburri said the scale and duration of the mass lay-up created unusually favorable conditions for invasive species to spread once ships resume global operations.

The unprecedented scale and duration of this spring and summer mass lay-up of large commercial ships has created ideal conditions for a marine invasive species ‘super-spreader’ event.

Carolyn Tepolt, a Woods Hole biologist who studies marine invasive species, warned that such species can cause major ecological and economic damage and can be extremely difficult to remove after becoming established.

The Asian green mussel is cited as an example of the risk. The species, common in warm waters including the Gulf, has previously spread by shipping to other regions and displaced local mussel populations.

Reaction and Response

The study's authors are calling for ship operators, port authorities, regulators and environmental managers to coordinate before the backlog disperses. Recommended measures include estimating biofouling levels before departure, forecasting vessel routes and first ports of call, improving early detection at high-risk ports and creating rapid alert networks.

Reports also say divers have been deployed at Gulf ports to clean hulls and propellers, although operational constraints may prevent every vessel from being treated before departure. Cleaning costs were reported at around $8,000 per ship in some cases.

For U.S. ports, the concern is indirect but significant: vessels leaving the Gulf can resume international routes and potentially carry warm-water organisms into new marine environments. The risk depends on where ships travel, what species are attached and whether those organisms survive and establish themselves after arrival.

What to Watch

The next major question is how vessel operators and port authorities handle the eventual restart of large-scale traffic through the Strait of Hormuz. Researchers are particularly focused on whether ships receive hull assessments or cleaning before departure and whether destination ports increase surveillance.

The exact ecological impact cannot be determined until vessels begin moving and their routes are known. The study's warning is preventive: once invasive species establish themselves in a new coastline, controlling or eradicating them can be exceptionally difficult.

FAQ

Why are ships near the Strait of Hormuz considered an invasive species risk?

Ships sitting idle for months can accumulate algae, barnacles, mussels and other organisms on their hulls. Those organisms may travel to new ports when the vessels begin sailing again.

How many ships are affected?

Researchers and reports describe more than 1,500 commercial vessels laid up in the Persian Gulf, with additional ships waiting in the nearby Gulf of Oman.

What is biofouling on a ship?

Biofouling is the buildup of marine organisms on submerged surfaces such as hulls, propellers and seawater systems. It can spread invasive species and increase drag, fuel use and emissions.

Can ships be cleaned before they leave the Gulf?

Yes. Researchers recommend assessing and, where practical, cleaning fouled hulls before departure, although limited maintenance capacity and operational pressures may prevent every ship from being treated.

Could this affect the United States?

Potentially. Ships returning to global trade routes may reach ports around the world. Researchers are calling for monitoring at high-risk destinations to detect non-native species early.