The extended closure of the Strait of Hormuz has left roughly 1,500 large commercial vessels immobilized in the Persian Gulf. International marine biologists warn that this unprecedented downtime risks triggering a global biological invasion through unchecked organism growth on ship hulls.
When geopolitical tensions shut down a critical maritime chokepoint, the immediate focus usually centers on energy supplies and shipping lanes. But a team of 24 international researchers, writing in the journal Biological Invasions, has turned attention toward a quieter, potentially permanent fallout: the ecological threat brewing on the underwater surfaces of trapped vessels.
Since the strait’s closure on February 28, 2026, an immense fleet has remained anchored in the shallow, warm waters of the Persian Gulf and the Gulf of Oman. According to data cited by international marine biologists, more than 1,500 large merchant vessels sit motionless, alongside hundreds of others anchored nearby. Commercial ships in the region typically turn around within one to three days, keeping hull colonization minimal. Months of inactivity, however, have stretched those port calls to roughly forty times their normal duration.
How Biofouling Accelerates During Extended Immobilization
The biological process known as biofouling follows a predictable timeline that accelerates dramatically under static conditions. As the study’s lead author, University of Maryland marine ecologist Mario Tamburri, explained, any artificial structure placed in the marine environment immediately attracts microbes, forming a biological film.
This biofilm is then colonized by the spores of macroalgues like the laminaires, or by the larves d’invertébrés, like the balanes, or by des vers, etc. These communities croissent et s’étendent ensuite car elles ont besoin de surfaces dures pour vivre. Mario Tamburri, University of Maryland
Because the Persian Gulf features a seafloor composed primarily of silt, mud, and sand, hard surfaces are scarce. Stationary ship hulls provide a rare, expansive habitat. Studies measuring immobilization windows show that between 10 and 28 days, biofouling accumulation multiplies by 13 to 25 times. After 28 days, more than 85% of test surfaces typically show colonization.
Compounding the problem, the closure began just as spring temperatures started warming the water. This seasonal shift triggers reproduction among sessile invertebrates and algae, creating ideal conditions for rapid growth across the submerged portions of the anchored fleet. Researchers note that these accumulations include not only visible macrofauna, but also bacteria, algae, crustaceans, and non-indigenous pathogens.
Global Vulnerabilities and Potential Destination Ports
Once authorities reopen the corridor and vessels resume transit, these accumulated organisms will travel alongside global cargo. Research institutions including the Smithsonian and the KAUST University in Saudi Arabia note that 57 distinct biofouling species from the Persian Gulf’s western coast could easily detach and colonize ports worldwide.
The earliest stops in the Middle East, the Indian subcontinent, and Southeast Asia face immediate exposure. In Europe, marine biologists specifically highlight the ports of Piraeus in Greece, Algeciras in Spain, and Rotterdam in the Netherlands as critical nodes requiring heightened surveillance.
Regulatory Shortfalls and the Debate Over Ballast and Hull Management
While international shipping hubs maintain strict protocols for ballast water, hull cleaning remains subject to far fewer mandatory controls. Major ports note that regulations govern ballast discharges. In Antwerp, port spokesperson Lennart Verstappen emphasized that mandatory onboard treatment systems eliminate most organisms in ballast water, and residue recovery during hull maintenance must be handled by licensed firms.
However, external hull scrubbing standards remain largely advisory. The International Maritime Organization recommended in 2023 that vessels docked long-term take precautionary measures before sailing, but the study’s authors warn that current regulatory frameworks and in-water cleaning capacities are entirely inadequate for an immobilization event of this magnitude.
Furthermore, the accumulation of organisms on wetted hull surfaces creates biosecurity risks that stressed marine ecosystems struggle to absorb.
What Lies Ahead for Biosecurity Interventions
Preventing widespread ecological disruption will depend heavily on pre-departure inspections, specialized cleaning protocols, and coordinated international oversight before ships leave the gulf. Researchers stress that monitoring receiving ports along major trade routes will be essential once traffic resumes.
As diplomatic negotiations regarding the waterway remain unresolved, the ultimate scale of the biological fallout rests on how quickly and strictly maritime authorities enforce hull sanitation protocols before the anchored fleet disperses.
Keep reading
