Deep-sea mining risks disrupting the marine food web, study warns

Mineral drilling deep in the ocean could have huge consequences for the tiny animals at the core of the vast marine food web, and ultimately impact fisheries and the food we find on our plates, according to a new study.

deep sea mining means drilling into the seabed in search of “polymetallic nodules” loaded with important minerals, including copper, iron, zinc and others. Although these minerals have not yet been commercialized, countries are pursuing deep-sea operations amid growing demand for these minerals for electric vehicles and other parts of the energy transition, as well as for technology and military uses.

Researchers examined water and waste collected during the 2022 deep-sea mining trials.

What the study found

University of Hawaii researchers studied an area of ​​the Pacific Ocean called the “twilight zone,” located approximately 650 to 5,000 feet (200 to 1,500 meters) below sea level. Their peer-reviewed findings, published Thursday at Natural communications The scientific journal says mining waste can affect everything from tiny shrimp less than 0.08 inches (2 millimeters) long to fish 2 inches (5 centimeters) long.

That's because after mining companies bring the mineral-rich nodules to the surface, they have to dump the excess seawater. ocean dirt from the floor and sediment back into the ocean. This creates a turbid plume of particles about the same size as naturally occurring food particles that would normally be eaten by zooplankton swimming at that depth.

This is slightly more than half of the ocean's zooplankton. If these organisms eat waste particles—what study senior author Brian Popp calls “junk food”—then it affects the 60% of micronekton that eat zooplankton.

And this malnutrition is a problem because these tiny organisms provide food throughout the food chain, ultimately affecting commercially important fish such as mahi-mahi or tuna.

“Surface fish can dive deep into the water, and they feed on organisms at depth,” said Michael Dowd, lead author of the study and a graduate student in oceanography. “If these organisms at depth are no longer there because their food web has collapsed, then higher food webs and more commercial interests could be affected.”

Impact on water and alternative sources

While other studies have identified the negative environmental impacts of deep-sea nodule mining, the focus is often on the seafloor. This study examines the situation in mid-water.

The researchers said more work is needed to assess the appropriate quality and depth at which dirty water and sediment from offshore mining can be returned to the ocean. But they said returning the excess directly to the ocean floor or to other depths could be just as environmentally destructive as the Twilight Zone, just in different ways.

Popp said deep sea excavation may not be necessary and instead noted alternative sources of metals, including recycling batteries and electronics or sifting through mining waste and tailings.

“If only one company mines in one place, it will not affect the huge fishery. It won't affect huge amounts of water. But if many companies mine for many years and extract a lot of material, it will spread throughout the region,” Dowd said. “And the more mining happens, the bigger the problem it can be.”

Where is deep sea mining located?

It may not be practical to simply stop mining in the ocean. The International Seabed Authority, which regulates mining beyond national jurisdiction, has already awarded several exploration contracts.

In the US, President Donald Trump has expressed interest in deep-sea mining operations amid tense trade negotiations with China that have limited US access to a wide range of China's critical minerals. In April, Trump signed an executive order directing the National Oceanic and Atmospheric Administration to speed up the process of issuing permits for companies to mine the ocean floor, and in May the administration said it would consider selling mining leases off the South Pacific island of American Samoa. Last month, NOAA sent draft rules to the White House to streamline operations.

Environmental groups oppose deep-sea mining, citing not only direct harm to wildlife and parts of the sea, but also disruption of planet-warming carbon dioxide that is currently locked up in the ocean and its floor.

“The study clearly showed that the effects would not necessarily be limited by the depth of the plume release,” said Cheryl Murdock, a deep-sea scientist at Arizona State University who was not involved in the study. “The question is, are a few minerals worth potentially disrupting the functioning of the oceans?”

Diva Amon, marine biologist and a researcher at the University of California, Santa Barbara, praised the study for exploring the potential implications.

“All this can lead to diseases of species, their movement, and death of species. And depending on the scale of it, it could have more serious consequences, such as species extinction,” said Amon, who was not involved in the study but has previously worked with some of the researchers.

“Much more research needs to be done to make informed decisions about how to manage this industry, if it does start, in a way that prevents, in fact, serious damage to the ocean and the ocean ecosystem.”

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