Study highlights new opportunities for marine protection in the deep Pacific mining zone

Image of the seldom seen Clarion Clipperton Zone (CCZ) courtesy of the National Oceanography Centre and the Trustees of the Natural History Museum, with acknowledgement to the NERC SMARTEX project

Protected areas have been set up to shield deep-sea life from the impacts of seabed mining in the Pacific Ocean. However, new research led by scientists at Plymouth Marine Laboratory (PML) and published in Nature Ecology & Evolution, highlights an opportunity to make these protections even more effective.

The study suggests that adding a small number of strategically located protected areas could help transform existing reserves into a more connected network, enabling tiny drifting larvae that have been cast adrift after disturbance to recolonise more successfully.

The research team focused on the Clarion Clipperton Zone (CCZ), a stretch of abyssal seafloor in the central Pacific roughly the size of Europe, lying around 5,000 metres down. This area has become a global hotspot for prospecting because its floor is scattered with polymetallic nodules, which are potato-sized lumps of rock rich in nickel, cobalt and other metals used in all electronics.

More than 1.1 million square kilometres of the CCZ are already licensed for mining exploration, and commercial extraction could begin within years. However, governments, scientists and environmental groups have long been concerned about the significant impact mining operations would have on these types of valuable habitats.

Why protecting the abyssal seafloor matters…

• Habitat scale: The abyssal seafloor is a vital and globally significant habitat that covers over 50 percent of Earth’s surface.
• Carbon cycling: The muddy plains play a critical role in the global carbon cycle by sequestering carbon and regulating climate.
• Biodiversity support: Despite the extreme cold, crushing pressure and total darkness, the seafloor supports unique microbes, invertebrates and fish.
• Mineral substrates: features like the highly-sought after polymetallic nodules offer hard surfaces for sponges and corals to grow in an otherwise soft sediment landscape.

To protect biodiversity from the impact of mining, the International Seabed Authority set aside a network of 13 ‘no-mining’ reserves, called ‘Areas of Particular Environmental Interest (APEIs)’, covering nearly two million square kilometres. The reserves were chosen mainly to represent a spread of different seafloor habitats but ensuring that marine life in one reserve could help replenish another if it was damaged was not a key consideration.

Using computer models of ocean currents across the whole CCZ, the PML-led team, that included partners from the National Oceanography Centre (UK), University of Plymouth (UK), Aarhus University (Denmark) and the Joint Nature Conservation Committee (UK), tracked the likely journeys of larvae drifting just above the seabed, where deep-sea larvae are known to concentrate.

The team found that even larvae capable of drifting for over two months typically travelled less than 100 kilometres. In contrast, the protected reserves sit between 200–800 kilometres apart, and fewer than two in every 10,000 simulated larvae released from one reserve ever reached another.

Dr Molly James, lead author of the study and a Marine Ecosystems Modeller at PML, commented:

“The existing deep-sea reserves are distributed across the ocean but with significant gaps between them. Our modelling suggests that rather than functioning as a connected network, they currently operate more as separate conservation areas.”

The researchers also modelled what would happen if mining went ahead and disturbed larval supply within the licensed mining areas themselves. Under that scenario, the protected reserves currently contribute only a small fraction of the larvae needed to help mining-affected areas recover, with most replenishment instead coming from the seafloor nearby that has no legal protection at all.

The team then used the same models to identify where new protected ‘corridors’ could be added to stitch the existing reserves together. Adding a small number of carefully chosen extra sites, covering a relatively modest area and mostly outside current mining claims, was enough to link every reserve into a single connected network.

This increased simulated larval exchange between reserves by more than 400-fold and under a mining-disturbance scenario, the contribution of protected areas to replenishing damaged sites nearly doubled.

Professor Kerry Howell, senior author on the study and Ocean Challenge Lead for Biodiversity Loss at PML, added:

“Our study shows that the current network is not ecologically coherent. Adding these corridors will move the network to something theoretically more effective at conserving biodiversity and aid recovery should mining go ahead.” 

The International Seabed Authority is currently considering how to strengthen environmental protection in the CCZ ahead of possible mining approvals. The authors say their approach, using freely-available ocean circulation data rather than scarce biological surveys, could be applied to other deep-sea regions facing similar pressures and wherever detailed ecological data are lacking.

The researchers caution that their models simulate the physical possibility of dispersal driven by ocean currents near the seabed, rather than proving that populations actually exchange genes or recover this way in practice. Testing these will require future fieldwork, including direct current measurements and genetic sampling in the areas the models highlight for protection.

The research was carried out as part of the ‘Seabed Mining and Resilience to Experimental Impact (SMARTEX)’ project, which examines how deep-sea ecosystems might respond to and recover from mining disturbance.