Deep-sea mining trial sharply reduced seabed animal count, diversity — study

[Ben Graham]

The potential ecological consequences of deep-sea mining gained urgent attention recently after a team of European researchers, through collecting data from an industrial trial, reported a sharp reduction in seabed animal abundance and species richness.

The study — led by scientists from the Natural History Museum, University of Gothenburg and National Oceanography Centre — involved tracking a deep-sea mining machine in the depths of eastern Pacific Ocean to decipher its potential impact on marine species over a two-year period.

With baseline data tracking 3,000 tonnes of polymetallic nodules at a depth of 4,280 metres, the study represents the largest ever conducted on assessing impacts of deep-sea mining on marine life. The entire project took five years to complete, with the research team spending over 160 days at sea and three years of analytical work in the laboratory.

The results were published last week on Nature Ecology & Evolution. According to the study, the density of macrofaunal animals — organisms visible to the naked eye — decreased by 37% within the mining tracks over the sampling period, while the species richness decreased by 32%.

Overview of study region, sampling design and example seafloor morphology. Credit: Eva Stewart et al., Nature Ecology & Evolution (2025)

“Being able to study these remote and poorly known deep-sea regions is extremely important as we consider the potential impacts of deep-sea mining,” Eva Stewart, a PhD student at the Museum and University of Southampton and lead author of the study, stated.

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

New species discovered

Stewart and other authors also noted that the expedition yielded discoveries, including a new species of marine animal (a solitaire coral) and how the abyssal ecosystem can naturally change over time.

A total of 4,350 sediment macrofaunal animals were collected across four expeditions, from which 788 species were identified by the collective efforts of the institutions involved in the study. The animals found were mainly marine worms (polychaete annelids), closely followed by crustaceans (isopods, tanaids, amphipods) and molluscs such as snails and clams.

Given that most of the animals were macrofaunal organisms living in sediment, it remains to be seen how deep-sea mining would impact other types of marine life. Still, the study points to a potentially large disturbance of the ecosystem based on its tracking on nodule-living animals alone.

The study was requested by Nauru Ocean Resources (NORI), a wholly owned subsidiary of The Metals Company (TMC), which has been looking to mine the Clarion–Clipperton Zone (CCZ) — a 6 million km² area of the central Pacific Ocean.

Concerns over seabed mining

The study results cast further doubts on whether mining the ocean floor presents a viable option to expand the global quest to extract critical minerals such as cobalt, nickel and rare earths, which are found in abundance in polymetallic nodules. The CCZ alone is estimated to hold over 21 billion tonnes of these minerals.

Greenpeace, an environmental organization that has long fought against the idea of deep-sea mining and companies like TMC, said the study serves as further scientific evidence of the significant damage mining activities can have on the ocean ecosystem.

“A test with machines only half the size of those intended to be used reduced the number of animals found in the tracks by 37%. Deep-sea mining will devastate the unique and newly discovered marine creatures in the high seas,” Greenpeace said.

“We are just beginning to understand this deep-sea ecosystem, and yet the overwhelming evidence continues to point to the fact that deep-sea mining will cause irreversible harm.”