More than 1,500 commercial vessels stranded in the Persian Gulf due to the prolonged closure of the Strait of Hormuz could become carriers of invasive marine species, posing a significant ecological threat to coastal ecosystems across the world, according to a new international study.

Published in the scientific journal Biological Invasions, the research warns that the months-long maritime disruption has transformed idle cargo ships and oil tankers into floating ecosystems capable of transporting algae, barnacles, mussels, microbes and other marine organisms to ports worldwide once global shipping resumes.

Months of Anchoring Raise Ecological Concerns

The Strait of Hormuz has remained largely inaccessible since February 28, following the outbreak of hostilities involving the United States, Israel and Iran. As a result, hundreds of commercial vessels have remained anchored in the warm, highly saline waters of the Persian Gulf for nearly five months.

Researchers said such prolonged inactivity has accelerated biofouling—the accumulation of marine organisms on submerged parts of ships. Under normal conditions, commercial vessels remain stationary for only a few days, limiting biological growth. However, extended anchorage has allowed dense marine communities to develop on ship hulls.

Floating Habitats Could Spread Invasive Species

Scientists said the stranded vessels have effectively become floating habitats capable of transporting entire marine ecosystems across international waters.

The study highlighted that species native to the Persian Gulf are particularly resilient because they have adapted to survive extreme temperatures and high salinity. These characteristics could allow them to establish themselves rapidly if introduced into suitable coastal environments elsewhere.

Marine biologist Mario Tamburri, one of the study's researchers, noted that organisms capable of surviving harsh environmental conditions often become successful invasive species when introduced into new ecosystems.

Risks to Marine Ecosystems and Industries

Researchers warned that once international shipping resumes, millions of marine organisms attached to vessel hulls could be transported to ports around the world.

If these species establish themselves in new habitats, they could outcompete native marine life, disrupt fisheries, damage biodiversity and interfere with critical infrastructure, including power plant cooling systems and port facilities.

The study also suggests that some vessels may have already released large numbers of larvae into Gulf waters during their prolonged stay, potentially altering local marine ecosystems.

Economic Impact Beyond Environmental Damage

Apart from ecological concerns, biofouling also increases operational costs for the shipping industry.

According to the researchers, even a thin biological coating on a ship's hull can increase fuel consumption and greenhouse gas emissions by 20–25%, while heavy barnacle growth may push fuel usage up by more than 50% because of increased drag.

The report noted that shipping companies have started deploying specialised underwater dive teams to clean hulls and propellers before vessels resume operations. However, increased demand has reportedly driven hull-cleaning costs up by nearly 60%, with services now averaging around $8,000 per vessel.

Scientists Call for Immediate Preventive Measures

Researchers have urged governments, shipping companies and port authorities to implement mandatory hull inspections and cleaning procedures before stranded vessels are allowed to leave the Persian Gulf.

The International Maritime Organization (IMO) has also recognised biofouling as one of the leading pathways for the global spread of invasive aquatic species and is working towards establishing an international framework to improve biofouling management.

The study concludes that preventing invasive marine species from leaving the Persian Gulf would be significantly more effective and less expensive than attempting to control them after they establish themselves in ecosystems around the world.