Deep-sea mining impacts marine life for decades

Marine ecosystems in the deep ocean show little sign of recovery even decades after experimental mining, according to new research that raises major concerns about the long-term impact of future seabed mining operations.

Published in the journal Nature, the study examined a deep-sea mining test site in the North Pacific that was first disturbed in 1979. Forty-four years later, biodiversity in that area remains lower than in nearby untouched regions. 

The research team, which returned to the site in 2023 and 2024, worked in the Clarion–Clipperton Zone (CCZ), a vast abyssal plain about halfway between Hawaii and Mexico. 

Situated 5,000 meters below the ocean surface, this deep seabed region holds rich reserves of polymetallic nodules – potato-sized mineral lumps containing metals like cobalt, nickel, and manganese, all crucial for clean energy technologies.

The study was led by scientists at the National Oceanography Center in Southampton and involved a consortium of British institutions, including the Natural History Museum, the British Geological Survey, Heriot-Watt University, and several universities. 

Together, the experts form SMARTEX (Seabed Mining and Resilience to Experimental Impact), a project funded by the UK’s Natural Environment Research Council.

Long recovery from deep-sea mining 

The original mining test involved a mechanical seabed rake that stripped nodules from a 14-meter-wide path. Despite the small scale and brief duration of the experiment, the site still bears visible scars. 

Areas stripped of nodules and track marks from the mining machine are clearly evident. The surrounding biological communities have yet to fully rebound.

“To tackle the crucial question of recovery from deep-sea mining, we need first to look to the past and use old mining tests to help understand long-term impacts,” said Professor Daniel Jones, the study’s lead author. 

“Forty four years later, the mining tracks themselves look very similar to when they were first made, with an 8-meter-wide strip of seabed cleared of nodules and two large furrows in the seafloor where the machine passed.” 

“The numbers of many animals were reduced within the tracks but we did see some of the first signs of biological recovery.”

Life that clings to nodules

The Clarion–Clipperton Zone covers over six million square kilometres – 25 times the size of the UK – and holds an estimated 21 billion tons of nodules. These nodules are essential to the deep-sea ecosystem, offering a rare hard surface for life to cling to in an otherwise sediment-heavy environment. 

“These nodules are potato-sized mineral deposits that have built up in layers over thousands of years. Mining companies want to mine these for critical metals like cobalt and nickel,” said Mark Hartl, a marine ecotoxicologist from Heriot-Watt University and co-author of the study.

“But there are so many unanswered questions. For example, we know the nodules produce oxygen. If they’re removed, will that reduce the amount of oxygen in the deep sea and affect the organisms that live there?”

“What is the effect of animal exposure to metal-containing sediment plumes churned up during the mining process? These are some of the questions we’re trying to answer.”

Biological impacts of deep-sea mining 

Hartl’s work focused on the biological effects of sediment exposure. He developed new methods to evaluate whether mining damages DNA in deep-sea fish. 

“This has never been done before,” said Hartl. “So we had no baseline data to compare any effects of mining against. We are currently optimising tests for other signs of stress applicable to the deep sea.”

Recovery may be measured in centuries

The deep sea’s slow pace of life is one reason recovery is so limited. Many organisms grow slowly, reproduce infrequently, or are adapted to highly specific habitats. 

“General ecological theory will predict that following disturbance, any ecosystem will go through a series of successional stages of recolonization and growth,” said Adrian Glover of the Natural History Museum.

“However, until this study, we had no idea of the timescales of this critical process in the deep-sea mining regions, or how different parts of the community respond in different ways.”

“Our results don’t provide an answer to whether deep-sea mining is societally acceptable, but they do provide the data needed to make better informed policy decisions such as the creation and refinement of protected regions and how we would monitor future impacts,” Glover added.

A question of future trade-offs

The International Seabed Authority (ISA), the organization responsible for managing mineral-related activity in international waters, currently maintains a moratorium on commercial deep-sea mining. It is still developing a legal and environmental framework to guide future exploitation, and the SMARTEX research may influence how those guidelines take shape.

In their paper, the scientists note that mining operations are expected to cause “immediate impacts” to seafloor habitats. Collector vehicles will remove nodules, compact sediments, and stir up sediment plumes that may travel beyond mining sites. These plumes, they argue, could have “significant impacts on ecosystems” well outside the directly affected zones.

While proponents of deep-sea mining argue that it could provide critical materials for a net-zero future, the study underscores that such gains may come at a long-term ecological cost. The scars of the past, still visible and measurable after 44 years, may well be a preview of the risks ahead.

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