Ecological cost of US-Iran war: Scientists warn ships stranded for months in the Strait of Hormuz could now carry invasive species, posing an ‘immense international biosecurity threat’

As commercial ships slowly begin moving through the Strait of Hormuz again after months of disruption caused by the US-Iran war in the Middle East, scientists have warned of a hidden ecological consequence: vessels that spent weeks or months stranded in the Gulf may now be carrying dense communities of invasive species and marine organisms to ports around the world.

An international team of marine scientists has warned that the prolonged shutdown could trigger a large-scale marine bioinvasion, as organisms that colonized stationary ships during the disruption are transported along global shipping routes once the vessels resume their journeys.

The warning was published in July 2026 in Biological Invasions in a paper titled “Closure of the Strait of Hormuz may trigger a bioinvasion super-spreader event.” The study was led by Mario N. Tamburri, a scientist at the University of Maryland Center for Environmental Science, along with an international team of marine researchers.


The timing has now become particularly important. Shipping through the Strait has begun to increase, although traffic remains well below normal levels. Reuters reported 10 visible commodity-vessel transits on August 27, compared with eight the previous day and a 10-day moving average of 15. The US military has also said it cleared sea mines from internationally recognized shipping lanes, while Iran continues to dispute the US characterization of the waterway's status.

That means the ecological scenario described by the scientists is no longer simply about ships sitting idle. The ships are starting to move again, potentially carrying months of accumulated marine life with them.

Why months of stranded ships could become an ecological problem

The Strait of Hormuz connects the Persian Gulf with the Gulf of Oman and the Arabian Sea and is one of the world's most important maritime chokepoints. In 2024, around 20 million barrels of oil per day moved through the strait, equivalent to about 20% of global petroleum liquids consumption, according to the U.S. Energy Information Administration.

But the scientists' concern is not primarily about oil. It is about what happened to the ships themselves while they were trapped. The researchers estimate that more than 1,500 large commercial vessels remained idle in the Persian/Arabian Gulf and Gulf of Oman after the Strait of Hormuz was closed on February 28, 2026.

Normally, commercial vessels spend only a few days in port before continuing their journeys. These ships were stationary for far longer. And that creates an ideal environment for biofouling, the accumulation of microbes, algae, barnacles and other marine organisms on submerged parts of a vessel.

The researchers note that biofouling on static surfaces can enter a rapid growth phase after about 10 days. Ships affected by the Hormuz disruption had remained idle for at least 40 times longer than an average port stay.

The ships may have become floating nurseries for marine organisms

As the vessels remained stationary, their hulls and submerged structures provided surfaces on which marine organisms could attach, grow and reproduce. The researchers point to hulls, sea chests, rudders and piping systems as particularly vulnerable areas.

And the problem is not necessarily limited to organisms simply clinging to the ships. Some can reproduce during the lay-up period.

The paper gives the example of the cosmopolitan barnacle Amphibalanus improvisus, which can release up to 36 larvae per adult per day at 30°C.

Because of the high densities of organisms that can accumulate on submerged surfaces, the scientists write that “individual vessels may have released millions of larvae during this lay-up period.”

The warm conditions in the Gulf could make the situation even more significant. Summer surface-water temperatures can reach approximately 38°C, while the region is also highly saline. The researchers say the spring and summer 2026 lay-up provided favorable conditions for biofouling growth and reproduction.

Now the biological passengers could leave the Gulf

This is where the ecological risk becomes global. A ship that remained stationary for months could have acquired organisms from the Gulf on top of the organisms it was already carrying from its previous voyages.

When that vessel leaves the region, those organisms can travel with it. Most will probably fail to establish themselves at their destination.

But the researchers are concerned about the species that survive, reproduce and become established in ecosystems where they did not previously exist.

The paper describes the combination of prolonged ship lay-ups, biological accumulation and global shipping connectivity as an “immense international biosecurity threat.”

The researchers warn that the vessels could trigger a marine “bioinvasion super-spreader” event as normal maritime traffic resumes.

Global ports are at risk from the sea-borne invasive species

The potential reach is enormous because the affected vessels are connected to global maritime networks. The scientists specifically identify Mumbai, Jeddah, Colombo and Singapore among the higher-risk ports east of Hormuz, while Alexandria, Piraeus, Algeciras and Rotterdam are among those to the west.

Ports with environmental conditions similar to those of the Gulf could be particularly vulnerable because organisms adapted to warm, saline waters may have a greater chance of surviving and establishing there, thereby posing an invasion threat to local marine life.

The ecological consequences could last longer than the conflict

The researchers stress that this does not mean an unprecedented global invasion is inevitable. Instead, they are warning that the conflict has created an unusual set of conditions that could make marine invasions more likely.

They describe the prolonged mass lay-up of vessels as a major risk factor for the large-scale dispersal of non-indigenous species once shipping resumes.

In their conclusion, they write: “Whether it becomes a global bioinvasion super-spreader event will now depend less on the biofouling communities already present on vessels than on the speed, coordination, and effectiveness of the responses that follow.” That makes the next stage crucial.

The scientists recommend that ships be inspected for biofouling, that vessels be cleaned where possible before departure and that ports prepare for increased monitoring. They also call for authorities to forecast vessel routes and identify likely first ports of call so that high-risk destinations can prepare for incoming ships.

The concern around invasive species

Earlier research had already warned that prolonged ship lay-ups could increase the risk of marine invasions. A 2022 study published in Biological Invasions, titled “Global marine biosecurity and ship lay-ups: intensifying effects of trade disruptions,” examined how disruptions such as the COVID-19 pandemic and the 2021 Suez Canal blockage by the 400 m-long “Ever Given”, one of the largest container ships in the world, could leave ships stationary for unusually long periods.

Researchers found that these extended lay-ups give marine organisms more time to colonize ship hulls and other submerged surfaces, and increase the number of non-native species transported when vessels resume their voyages.

A different kind of fallout from the US-Iran conflict

The humanitarian and economic consequences of the US-Iran war have dominated, while the Strait of Hormuz has largely been discussed in terms of an energy and shipping crisis. But the scientists are highlighting another consequence that could emerge after the immediate disruption ends.

The conflict forced an extraordinary number of ships to remain stationary in one of the world's warmest marine environments for months. Now, as those ships begin moving again, the organisms that colonized them could potentially move with them.

The researchers warn that “The challenge is not simply to detect new species, but to identify emerging risks early enough to prevent their spread through highly connected global transport networks.”

In other words, reopening the Strait may restart an important artery of global commerce, but it could also begin the next phase of an ecological problem created during the shutdown. And unlike a tanker carrying oil, the biological cargo attached to a ship may be difficult to see until it reaches and thrives in a new ecosystem.