An international team of scientists has documented nearly 800 species, many previously unknown, living nearly 4,000 meters below the Pacific Ocean's surface. Their five-year study in the Clarion-Clipperton Zone also tested the environmental impacts of deep-sea mining, finding significant local reductions in animal numbers and diversity. The findings, published in Nature Ecology and Evolution, provide crucial data for regulating future extraction of critical metals.
The global push for critical metals essential to the green energy transition has intensified interest in deep-sea mining. In the Clarion-Clipperton Zone, a vast area between Mexico and Hawaii, researchers conducted an extensive survey to assess both biodiversity and potential mining effects.
Over five years, involving 160 days at sea, the team followed guidelines from the International Seabed Authority (ISA) for baseline studies and impact assessments. They collected 4,350 animals larger than 0.3 mm from the seabed, identifying 788 species, primarily marine bristle worms, crustaceans, and mollusks such as snails and mussels. Among the discoveries was a new solitaire coral species, detailed in a separate study.
Test mining in the area revealed direct disturbances: animal abundance dropped by 37 percent and species diversity by 32 percent along equipment paths. However, the overall environmental impact appeared smaller than previously anticipated. At depths where sunlight does not penetrate and food is scarce—with sediment accumulating at just one thousandth of a millimeter per year—life is sparse compared to shallower seas like the North Sea.
"Critical metals are needed for our green transition, and they are in short supply. Several of these metals are found in large quantities on the deep-sea floor, but until now, no one has shown how they can be extracted or what environmental impact this would have," said marine biologist Thomas Dahlgren from the University of Gothenburg, who co-led the identification of polychaete worms using DNA analysis.
The study highlights gaps in knowledge, as natural community shifts occur over time due to varying food supply, but species distributions remain unclear. "It is now important to try to predict the risk of biodiversity loss as a result of mining. This requires us to investigate the biodiversity of the 30 percent of the Clarion-Clipperton Zone that has been protected. At present, we have virtually no idea what lives there," noted senior author Adrian Glover from the Natural History Museum of London.
These insights will inform ISA regulations on mining in international waters, balancing resource needs with ecosystem preservation in one of Earth's least explored realms.