Credit: Natural History Museum

A new report reveals the results of a study exploring biodiversity in a region targeted for seabed mining—capturing baseline data, tracking natural changes and assessing the impacts of a polymetallic nodule mining machine. This represents the largest study of the impacts of deep-sea mining on seafloor animals.

Taking into consideration natural fluctuations, the study found that after the test, there was a 37% reduction in the number of macrofaunal animals living within the sediment directly impacted by the tracks of the deep-sea mining machine. Macrofaunal animals are organisms visible to the naked eye (0.3mm–2 cm in size), such as polychaete worms, crustaceans, snails and clams. No impact on animal abundance was detected in regions covered by a sediment plume from the mining machine.

In terms of biodiversity, the reduction in abundance of animals caused a 32% reduction in species richness in the directly impacted regions and an increase in the dominance of some animals in the areas impacted by the plume.

The research was led by scientists from the Deep-Sea Research Lab at the Natural History Museum and co-led by the University of Gothenburg and National Oceanography Center. The project took five years to complete, with the team spending more than 160 days at sea in the Pacific and three years of careful analytical work in the laboratory.

The resulting paper, "Impacts of an industrial deep-sea mining trial on macrofaunal biodiversity," is published in the journal Nature Ecology and Evolution.

Eva Stewart, lead author and Ph.D. student at the Museum and University of Southampton, said, "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. Finally, we have good data on what the impacts of a modern commercial deep-sea mining machine might be. We have also discovered many new species and shown how the abyssal ecosystem changes naturally over time."

Overview of study region, sampling design and example seafloor morphology. Credit: Nature Ecology & Evolution (2025). DOI: 10.1038/s41559-025-02911-4

The methodology and the findings

To separate the environmental impacts of the mining test from natural changes across space and time, the team needed to collect samples from control sites replicated over time and from sites chosen to be spatially equivalent to the area being impacted by the mining disturbance.

To ensure samples were taken inside the tracks created by the collector test, the team used a Remotely Operated Vehicle (ROV) to guide them, launched from the survey ship 4 km above.

A total of 4,350 sediment macrofaunal animals were collected across four expeditions, from which 788 species were identified by several institutions, including the museum. As is common for abyssal sediment communities, the animals found were mainly marine worms (polychaete annelids), closely followed by crustaceans (isopods, tanaids, amphipods) and mollusks such as snails and clams.

Dr. Thomas Dahlgren, Researcher at the University of Gothenburg and co-lead of the project said, "I have spent over 20 years working in the Clarion-Clipperton Zone, and this is by far the largest study we have ever undertaken. At Gothenburg, we led the identification of the polychaete worms, one of the most abundant groups. As most species are undescribed, molecular (DNA) data were crucial to aid the taxonomic studies and provide the core data for the ecological study."

The results published in the study show that against a background of strong natural variation—possibly driven by shifts in the El Niño Southern Oscillation—there were significant impacts of the mining test on several aspects of animal abundance and diversity.

Macrofaunal densities decreased by 37% within the path of the nodule collector, while densities within the control sites either increased or remained unchanged. The sites impacted by the plume of sediment from the mining machine approximately 400 m distant showed no change in faunal abundance but shifts in the dominance pattern of some animals. The team also reported a significant decrease in species richness within the mining tracks, although diversity measured by sample-size independent measures remained unchanged.

Communities overall were more variable after the mining test, with scientists noting a wider dispersal and patchiness of creatures. This pattern is consistent with findings from shallow water and terrestrial impact studies.

Dr. Tammy Horton, Researcher at the National Oceanography Center and co-lead of the project said, "At NOC, we are world-leaders in the identification of crustaceans, a very diverse and difficult group which is often overlooked in ecological studies. Many new species have been found during the study which are now being described, and we are ensuring that these data and specimens will be available for future study by all stakeholders. This new and very large ecological dataset was only possible through collaboration across several institutes with broad expertise in the different animal groups."

Dr. Adrian Glover, deep sea scientist at the Museum and senior author, said, "Thanks to a huge team effort from 14 authors and multiple institutions, the new data and interpretations can be used to inform the current policy discussion on deep-sea mining, providing actual quantitative data on species-level impacts. They will form a critical evidence base going forward, and, we hope, set a new standard for environmental work in the region, regulated by the International Seabed Authority (ISA)."

"Now it is important to try to predict the potential for biodiversity loss caused by mining. This will require us to survey and undertake taxonomic work in the regions set up by the ISA as large, protected areas across the CCZ. Currently we have no idea, for the most part, of what lives in them and thus what the risk is of biodiversity loss is in the potential mined regions."

The research team collected this information to ensure vital biodiversity data is available to everyone who has a stake in decisions on the sustainability of deep-sea mining, from the regulator to environmental pressure groups.

More information: Eva C. D. Stewart et al, Impacts of an industrial deep-sea mining trial on macrofaunal biodiversity, Nature Ecology & Evolution (2025). DOI: 10.1038/s41559-025-02911-4

This story is republished courtesy of Natural History Museum. Read the original story here.

Citation: Study measuring impacts of deep-sea mining machine finds abundance of animals at the site decreased by 37% (2025, December 7) retrieved 7 December 2025 from https://phys.org/news/2025-12-impacts-deep-sea-machine-abundance.html

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