Deep-sea mining may cause ocean animals such as fish and shrimp to vacate the surrounding areas for at least a year.
Some countries and companies are eager to exploit the sea floor as a rich source of minerals and precious metals, such as nickel, manganese and cobalt, that could be useful in the production of goods like electric car batteries.
However, not much is known about how mining the seabed for these materials might affect the surrounding wildlife. Commercial deep-sea mining operations have yet to begin, with talks currently taking place at the International Seabed Authority in Jamaica to formalise regulations governing the industry.
In 2020, Japan conducted a deep-sea mining test at the Takuyo-Daigo seamount, an underwater mountain about 900 metres below the surface of the north-west Pacific Ocean. In the test, a crust-excavator machine scraped the crust over 129 metres for a total of 109 minutes over seven days, spreading plumes of sediment through the surrounding waters as it went.
Travis Washburn at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, and his colleagues took the opportunity to investigate the impact of the test on the local marine wildlife.
A month before the test, the researchers deployed a remote underwater vehicle to record videos of the megafauna – animals larger than 1 centimetre – present in the 300-square-metre area around the test site. They then repeated this one month and 13 months after the completion of the test.
For stationary organisms, such as sea sponges, sea anemones and corals, their populations remained stable throughout the study period.
For highly mobile organisms, such as fish, shrimp and comb jellies, their numbers over a year after the test were 43 per cent lower in the areas that were directly affected by sediment displacement compared with before the test. They were also 53 per cent lower in the areas adjacent to the sediment plumes, which suggests that the most mobile animals may avoid even the periphery of the mining areas, says Washburn.
“Considering that this was a very small mining test in area and time, directly impacting a few hundred square meters over a period of days, full-scale mining covering 10 to 100 square kilometres and lasting for years could cause disruption of the mobile megafauna over entire seamounts for long periods,” says Craig Smith at the University of Hawaiʻi at Mānoa, who wasn’t involved in the study.
The prospects for deep-sea mining remain uncertain, with some countries, including Canada, New Zealand and France, calling for a ban or moratorium on the practice.
It is crucial to understand how deep-sea mining will affect marine ecosystems, says Washburn. “For mining regulations, you have to know how far an area is impacted,” he says. “You have to have preservation zones, which could extend that footprint of the mining a decent amount.”
“For the swimming animals to stay away from test-mined sites and adjacent areas for so long is a worrying sign that commercial mining would have even worse and wider environmental impacts than previously thought,” says author and marine biologist Helen Scales. “This study highlights how important it will be to do a lot more scientific research in order to fully understand how mining will alter deep-sea ecosystems.”