Long-term impacts of deep-sea mining and first signs of biological recovery revealed
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A new study involving the University of Liverpool has revealed the long-term impacts and the first signs of biological recovery in seabed mining tracks, 44-years after deep-sea trials in the Pacific Ocean.
The findings, published in a paper in the journal Nature, provide critical evidence to the global deep-sea mining debate.
The concerns around deep-sea mining and the impact on the marine environment are heightened by a lack of evidence and understanding of the long-term recovery of the ecosystem.
The study involved a team of scientists including Dr Rachel Jeffreys, Louisa Norman and Sabena Blackbird from the University of Liverpool’s Department of Earth, Ocean and Ecological Sciences.
The international research team recently visited a previously mined site in the Clarion Clipperton Zone (CCZ) to investigate if recovery is possible and what impact remains 44 years after the machines have left.
They found that mining has clearly caused long-term changes to the sediments but the effects on the animals living at these depths is more variable.
Lead author and expedition leader, Professor Daniel Jones of the National Oceanography Centre explains: “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. Forty-four years later, the mining tracks themselves look very similar to when they were first made, with an 8-metre-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.”
“We found some recovery of small and mobile animals living on the sediment surface. A type of large amoeba-like xenophyophore, creatures commonly found everywhere in the CCZ region, had recolonised the track areas. However, large-sized animals that are fixed to the seafloor, are still very rare in the tracks, showing little signs of recovery.”
The team also discovered that sediment plumes, previously considered to be a likely major impact on the seafloor community, had limited long-term physical impacts and no detectable negative effects on animal numbers in the study.
“The evidence provided by this study is critical for understanding potential long-term impacts. Although we saw some areas with little or no recovery, some animal groups were showing the first signs of recolonisation and repopulation” added Professor Jones.
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National Oceanography Centre and Trustees of the Natural History Museum, with acknowledgement to the NERC SMARTEX project.[/caption]
Sinking particles and sediments are the main food source for many deep-sea animals in the Clarion Clipperton zone. Deep-sea mining directly impacts the top layer of the sediment and could potentially alter the food available for animals living in areas where mining might take place.
The work undertaken by the team at Liverpool aimed to understand if deep-sea mining alters the composition of the food available to deep sea animals.
Dr Rachel Jeffreys studies food webs in the ocean and said: “At first glance there was no difference in the amount of food available between the mining tracks and surrounding sediments, however food availability was patchier within the mining tracks, indicating disturbance of key food resources.”
Co-author, Dr Adrian Glover, from the Natural History Museum, said: "General ecological theory will predict that following disturbance, any ecosystem will go through a series of successional stages of recolonisation and growth. 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."
Deep-sea mining is increasingly being considered as a potential solution to supply the crucial metals required for advancing global technology and driving the transition to a net zero energy future.
A key area of interest for mining is the CCZ, a vast region in international waters of the Central Pacific Ocean. Spanning over 6 million square kilometres, approximately 25 times the size of the UK.
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Image credit: National Oceanography Centre and Trustees of the Natural History Museum, with acknowledgement to the NERC SMARTEX project[/caption]
It is home to unique and biodiverse deep-sea creatures, many yet to be described by science, as well as a rich mineral resource of polymetallic nodules, highly enriched in metals. At depths of nearly 5,000m on the seabed of the CCZ, the abundant potato-sized rocks represent one of the most promising deep-sea mineral resources.
The International Seabed Authority (ISA), established in 1994 under international law, is deciding whether to allow deep-sea mining in the region and under what conditions. A key question in this decision, is whether deep-sea ecosystems can recover from mining disturbances.
In the 1970s the first of industrial trials of deep-sea mining were carried out in the Pacific. It was this site that Prof. Jones and his team visited in 2023, onboard the world-class Royal Research Ship James Cook, equipped with the cutting-edge underwater robot submersible Isis, to explore and study the aged mining tracks deep beneath the ocean's surface.
The paper ` Long-term impact and biological recovery in a deep-sea mining track' (doi: 10.1038/s41586-025-08921-3) is published in Nature
The study forms part of the Seabed Mining and Resilience To EXperimental Impact (SMARTEX) project – funded by the Natural Environment Research Council (NERC).
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RRS James Cook - SMARTEX Expedition. Image credit: National Oceanography Centre[/caption]