Scientists at the Woods Hole Oceanographic Institution warn thousands of stranded vessels could cause the spread of invasive marine life worldwide
An estimated 1,500 commercial vessels are currently anchored in the Persian Gulf amid a complete breakdown in diplomatic talks between the US and Iran. With many of the ships stranded since the Strait of Hormuz closed four months ago, scientists are now warning that conditions could be leading to a global marine bioinvasion ‘super-spreader’ event.
Most cargo boats spend less than two days in port, but the longer they remain stationary, the more they tend to accumulate communities of marine organisms – algae, barnacles, mussels and other invertebrates that can colonise and multiply on ship hulls. It often takes just 10 days for organisms living on static surfaces to reach a rapid growth phase. A new report, led by researchers at Woods Hole Oceanographic Institution (WHOI), says that when these vessels finally return to their normal trade routes, any marine species they’ve amassed could be transported around the world.
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Modern shipping has long been recognised as one of the primary pathways for marine invasive species to spread. There have been previous incidents where ships have been laid-up – such as when the Ever Given ran aground in the Suez Canal in 2021, bringing traffic to a halt for six days. Research has linked the European invasion of the Australasian barnacle Austrominius modestus to the Second World War, when New Zealand ships spent extended layovers in English ports. But the scale and duration of the recent vessel lay-up is unlike anything previously documented, creating what the researchers call an ‘unprecedented’ global biosecurity challenge.
‘Marine invasive species have profound ecological and economic impacts on coastlines across the globe and are extremely difficult, if not impossible, to eradicate once they become established,’ says Carolyn Tepolt, a biologist at WHOI. ‘This disruption to global shipping has many repercussions and has also more quietly created ideal conditions to spread warm-water species to new ports.’
Focusing on a ‘worst-case scenario’, the researchers highlight how conditions in the gulf – where harmful algal blooms have become a recurrent and escalating issue – have likely fostered stress-tolerant marine life adapted to high salinity, temperatures, and pollution. These organisms are more likely to survive transport and establish in new regions, where they can act as vectors for non-indigenous parasites and pathogens.
While the International Maritime Organization recommends that vessels that have been anchored for more than 18 days undertake immediate action to manage biofouling, there are concerns that vessels – and crews – that have been stranded for so long will defer necessary maintenance until their next port of call.
To avert a pending ecological crisis, the authors are calling for a coordinated global response that encompasses pre-departure estimates of biofouling, the identification of first ports of call, and heightened surveillance at high-risk ports.
