Idle ships in the Gulf and invasive species

When the Strait of Hormuz closed on 28 February 2026, more than 1,500 large commercial ships were left idle in the Persian/Arabian Gulf and the Gulf of Oman.^1,3 Ships there normally spend one to three days in port; by July these had sat at least 40 times longer.¹ A hull at anchor grows a slime of microbes, then algae, barnacles, mussels and other animals, and Gulf water in summer can reach 38°C with very high salinity, so what survives there is hardy.^1,2 In July 2026, 24 scientists led by Mario Tamburri of the University of Maryland Center for Environmental Science published a warning in Biological Invasions.¹ When these ships sail, they could spread Gulf species, and species they brought from elsewhere, to ports around the world.^1,2 Once such species are established, notes Carolyn Tepolt of the Woods Hole Oceanographic Institution, which took part in the study, they are extremely difficult, if not impossible, to eradicate.² The sources give different counts: the paper says more than 1,500 ships; in mid-July the International Maritime Organization said 300 to 400 remained, not counting local vessels, and noted that ships switching off their tracking make any count uncertain.¹

Who needs an answer

• Port authorities and biosecurity agencies in high-salinity ports, which Tamburri expects to be most at risk; he says the work starts with the nearby region, the Mediterranean and most of Asia.¹
• Ship operators and the in-water cleaning companies in the Gulf, deciding which hulls to clean before departure. The capacity there is far short of the number of ships, and a director at one cleaning firm estimates about 98% of what is scraped off hulls worldwide is not captured.¹
• The International Maritime Organization, whose 2023 biofouling guidelines are not mandatory; it is working toward mandatory requirements, but a draft legal framework is not expected until 2029.¹

The domains it chains

Ship movements and how long each hull sat at anchor; water temperature and salinity at anchor and at each destination; the biology of the species on the hulls, including how much heat and salt they tolerate and how fast they breed; and the ports, fisheries and coasts that would bear the cost of an invasion.

What a twin should let people try

• Ranking ports: given where each ship goes next and how closely that port's water matches the Gulf's, which ports should set out monitoring first?
• Ranking hulls: with cleaning capacity for only a few ships, which ones carry the most risk?
• Early warning: the authors suggest a ship's loss of power through the water, compared with before the lay-up, as a rough measure of how fouled it is.¹ How well would that pick out the worst hulls?

Where to start

The authors plan to model ship routes, the chance of fouling for each vessel, and whether species survive the voyage, to find the highest-risk ports.¹ They recommend settlement plates (panels left in the water and checked for what grows) at high-risk ports, and fast warnings to port authorities and regional biosecurity networks.¹ For traffic through the strait itself, Portolan shows ships a day from IMF PortWatch's satellite ship-tracking.