Deep-sea mining causes immediate loss of seafloor life

From Earth by Eric Ralls

Far below the ocean surface, the deep seafloor is often described as one of the planet’s least disturbed ecosystems.
That assumption is now being tested.

Companies are preparing to mine mineral-rich nodules scattered across the abyss.
The shift raises urgent questions about how quickly damage could appear once industrial machines begin operating.

A new field experiment offers one of the clearest answers yet.
Researchers found that a single trial of a deep-sea mining collector physically removed more than one-third of the animals and species living directly in its path.

The results show that biological impacts can occur immediately, not only after years of full-scale extraction.

Examining the seafloor test tracks

The damage was documented along fresh tracks carved into the abyssal seafloor during a 2022 trial that removed thousands of tons of mineral-rich nodules from deep Pacific sediments.

By comparing conditions before and after the test, Eva C. D. Stewart and colleagues at the Natural History Museum (NHM) in London directly documented how animal communities thinned and simplified inside those tracks.

The decline appeared within months of the trial, standing out even against the strong natural ups and downs that shape deep-sea life over time.

That contrast between rapid disturbance and slower background change sets the boundary of what the evidence can already show and what the rest of the seafloor response still needs to reveal.

Nodules support seafloor life

Mining companies target polymetallic nodules – rock-like lumps on the seafloor that contain valuable metals such as nickel, cobalt, and copper – because global demand for these materials continues to rise.

Across much of the deep ocean, these nodules sit scattered on soft mud and act as rare patches of hard surface.
Many animals attach to them or use them for feeding, shelter, and breeding.

When mining machines collect the nodules from the seafloor, they remove these living spaces along with the minerals.

Because so many species depend on the nodules themselves, the impact of mining must be measured in terms of habitat loss – not just the amount of metal extracted.

Tracks caused the biggest drop

Inside the fresh tracks, counts of macrofauna – seafloor animals visible without a microscope – fell sharply within two months.
The collector churned the top inch of sediment where most creatures live, and it left a bare lane behind.

With pre-mining sampling in hand, the team reported a 32 percent drop in species richness inside the tracks.

“Finally, we have good data on what the impacts of a modern commercial deep-sea mining machine might be,” said Stewart.

 

Plumes rewired the seafloor community

Far from the tracks, sediment plumes, clouds of stirred-up mud that drift and settle, changed who dominated without lowering animal totals.

The team sampled about 1,300 feet from the lane and saw a thin layer of sediment coating the nodules.

Animal counts stayed steady there, but a few species became more dominant, which reduced overall biodiversity in the plume zone.

Because plumes can spread beyond mined lanes, monitoring has to track community balance, not only head counts, across wide areas.

Natural cycles obscure damage

Animal densities rose and fell across the abyssal plain – a flat deep seafloor covered in fine mud – for two years before mining began.

Changes in surface winds and currents affected how much food reached the bottom, and seafloor communities responded.
These natural swings reduced animal numbers at several sites even before the test, making clean controls essential.

Without repeated sampling, managers could mistake a climate-driven decline for mining damage and draw the wrong boundary for protection.

Across 80 mud cores, the team sorted 4,350 animals and identified 788 species, though diversity remained under-sampled.
Projections suggested that about 15,000 individuals, or 400 cores, would be needed to capture most species.

Researchers tracked species richness – the number of different species per core – which often falls when mining reduces animal communities.

“We have also discovered many new species and shown how the abyssal ecosystem changes naturally over time,” said Stewart.

Mining recovery may take decades

Evidence from past tests suggests recovery will be slow and uneven.
A separate study tracking a 1979 mining test strip still found strong disturbance 44 years later.

Deep-ocean sediments mix slowly, and replacing removed nodules takes far longer than human lifetimes, so communities rebuild at a crawl.

Some small, mobile creatures returned, but many larger animals remained reduced where the seafloor had been scraped.
This history suggests fresh tracks may persist for decades, meaning the early losses measured today could be only the first signal.

Understanding those long-term changes will require stronger monitoring.
Future surveys must include enough sediment cores to capture natural variation, with at least five recommended per site.

Additional cores reduce the chance that a single unusually rich or sparse sample drives the result, especially when animals cluster in patches.

Surveys will also require specialists to identify animals to the species level.
Without that detail, monitoring could miss which species disappear first and fail to detect slower ecological shifts outside mined tracks.

Seafloor evidence fuels mining debate

The International Seabed Authority has signed 15-year exploration contracts with 22 contractors, while industry continues to push for rules governing commercial mining.

Regulators already require baseline surveys and environmental impact plans, and these new results highlight why both must include long-term time-series monitoring.

In the recent trial, Nauru Ocean Resources partnered with Allseas to operate the collector.
The trial demonstrated how mining activity can produce immediate seafloor damage alongside broader, subtler ecological changes that unfold over time.

Until extended follow-up data become available, policymakers will face a difficult decision about how much uncertainty they are willing to accept.

Continued monitoring will determine whether affected communities can recover.
The same rigorous sampling approach could help guide future permitting decisions or justify pauses as governments weigh economic demand against environmental risk.

Links :

• Nature Ecology & Evolution : Impacts of an industrial deep-sea mining trial on macrofaunal biodiversity
• Earth : Sediment clouds from deep-sea mining threaten seafloor life  
• Hydro : NOAA to map mineral-rich seafloor off American Samoa 
• Alaska Beacon : U.S. Interior Department agency solicits interest in seafloor mining off Alaska
• NYTimes : New U.S. Rule Aims to Speed Up Mining of the Seafloor