Prolonged shipping disruptions across the Strait of Hormuz could trigger a global spread of invasive marine species, as thousands of idle vessels accumulate heavy biofouling in warm, nutrient-rich waters, according to a peer-reviewed study published in the journal Biological Invasions. The ongoing geopolitical conflict has left more than 1,500 ships stranded in the Persian Gulf and hundreds more anchored in the Gulf of Oman, creating a severe international biosecurity threat.
Strait of Hormuz Shipping Blockade Drives Biosecurity Threat
The Strait of Hormuz connects the Persian Gulf with the Gulf of Oman, facilitating the passage of approximately 20% of the world’s oil supply, according to data from the U.S. Energy Information Administration. Following military escalations that began in February, Iran has intermittently restricted tanker traffic through the critical waterway. Last week, the United States resumed a naval blockade on the strait after Iranian forces fired upon oil tankers.
This chokehold on maritime traffic has trapped thousands of commercial vessels in prolonged stationary periods. According to Mario Tamburri, a marine ecologist at the University of Maryland’s Center for Environmental Science and lead author of the study, extended downtime causes extensive biofouling on ship hulls. Microorganisms, algae, plants, and invertebrates attach to the vessels and travel globally as ships resume routes from port to port.
Hardy Marine Organisms Increase Invasion Risks
The ecological characteristics of the Persian Gulf and the Gulf of Oman amplify the threat. Organisms native to this region are exceptionally hardy and robust because they have evolved to survive high salinity and elevated water temperatures, according to Tamburri. These physiological traits make them uniquely suited to endure long ship voyages and successfully colonize foreign ecosystems.
“All these marine organisms, invertebrates like barnacles and mussels and algae—they start growing and reproducing,” Tamburri told ABC News. “They start growing and reproducing, and they’re sitting in this warm soup of nutrient-rich water.”
The study notes that summer heat is exacerbating water temperatures in the region, creating what researchers describe as a worst-case scenario. Industrial ports and other stressed marine ecosystems are especially vulnerable to these bioinvasions, as environmental disturbances allow fast-growing opportunistic species to establish permanent populations.
Economic Damage and Historical Precedents
Once invasive species take hold in a foreign ecosystem, eradication is nearly impossible. Tamburri pointed to the historical spread of zebra mussels in North America. Native to the Caspian and Black Seas, zebra mussels multiplied rapidly in the Great Lakes during the 1980s and subsequently spread to the Mississippi and St. Croix rivers, as well as the West Coast via human transport. Ecologists have spent 50 years battling the species, according to Tamburri.
Invasive organisms inflict millions of dollars in economic damage by harming commercial operations such as aquaculture and fisheries while fundamentally altering local habitats, according to the research. While commercial vessels are typically coated with anti-fouling paints designed to prevent marine growth, these chemical coatings degrade when ships remain stationary for extended periods, mirroring heavy biofouling patterns observed during the COVID-19 pandemic.
Prevention Strategies and Port Regulations
Because eradicating marine invaders requires extreme and costly measures, experts emphasize prevention and early detection. Many shipping ports offer in-water cleaning services where divers scrape biofouling materials from hulls. Ecologists recommend utilizing vacuum-equipped cleaning devices to capture detached organisms rather than releasing live material back into the water.
“If at all possible, ships really need to try to clean their hulls before they leave,” Tamburri said.
Regulatory frameworks are also adapting to the risk. New Zealand currently mandates that all vessels entering its waters maintain a clean hull to mitigate biofouling pests, and the International Maritime Organization is pushing to strengthen global regulations. Moving forward, port authorities may increasingly turn away heavily fouled ships to protect local marine environments.