A study led by Plymouth Marine Laboratory (PML) has found that adding a small number of strategically located deep-sea protected areas could link the existing no-mining reserves in the Pacific’s Clarion Clipperton Zone (CCZ) into a single connected network. The research, published in Nature Ecology & Evolution, comes as commercial deep-sea mining in the region moves closer.
The researchers modelled how tiny drifting larvae could recolonise areas after disturbance. They found that the current reserves function largely as separate conservation areas rather than as a connected network.
A prospecting hotspot the size of Europe
The CCZ is a stretch of abyssal seafloor in the central Pacific roughly the size of Europe, lying around 5,000 metres down. It has become a global hotspot for prospecting because its floor is scattered with polymetallic nodules, potato-sized lumps of rock rich in nickel, cobalt and other metals used in electronics.
More than 1.1 million square kilometres of the CCZ are already licensed for mining exploration, and commercial extraction could begin within years. Governments, scientists and environmental groups have long raised concerns about the impact mining would have on these habitats.
According to PML, the abyssal seafloor covers over 50 per cent of Earth’s surface and plays a role in the global carbon cycle by sequestering carbon. It supports unique microbes, invertebrates and fish, while the nodules themselves provide hard surfaces for sponges and corals in an otherwise soft sediment landscape.
Reserves chosen for habitat rather than connectivity
To protect biodiversity, the International Seabed Authority set aside a network of 13 no-mining reserves, known as Areas of Particular Environmental Interest (APEIs), covering nearly two million square kilometres. The reserves were chosen mainly to represent a spread of seafloor habitats. Ensuring that marine life in one reserve could replenish another if it was damaged was not a key consideration.
The PML-led team included partners from the National Oceanography Centre, the University of Plymouth, Aarhus University in Denmark and the Joint Nature Conservation Committee. Using computer models of ocean currents across the whole CCZ, the team tracked the likely journeys of larvae drifting just above the seabed, where deep-sea larvae are known to concentrate.
Larvae rarely travel between reserves
Even larvae capable of drifting for over two months typically travelled less than 100 kilometres. The reserves, by contrast, sit between 200 and 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, said: “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 a scenario in which mining disturbed larval supply within the licensed areas. In that case, the reserves contributed only a small fraction of the larvae needed for recovery, with most replenishment coming from nearby seafloor that has no legal protection.
Corridors to connect deep-sea protected areas
The team used the same models to identify where new protected corridors could be added. 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 network.
This increased simulated larval exchange between reserves by more than 400-fold. Under the mining-disturbance scenario, the contribution of protected areas to replenishing damaged sites nearly doubled.
Professor Kerry Howell, senior author and Ocean Challenge Lead for Biodiversity Loss at PML, said: “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.”
Wider application and next steps
The International Seabed Authority is considering how to strengthen environmental protection in the CCZ ahead of possible mining approvals. The authors said their approach, which uses freely available ocean circulation data rather than scarce biological surveys, could be applied to other deep-sea regions facing similar pressures and where detailed ecological data are lacking.
The researchers cautioned that the models simulate the physical possibility of dispersal driven by near-seabed currents, rather than proving that populations exchange genes or recover this way in practice. Testing this will require fieldwork, including direct current measurements and genetic sampling in the areas highlighted 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. Further details are available in PML’s announcement of the study.
Frequently asked questions
What is the Clarion Clipperton Zone?
The Clarion Clipperton Zone is a stretch of abyssal seafloor in the central Pacific, roughly the size of Europe, lying around 5,000 metres down. Its floor is scattered with polymetallic nodules rich in nickel, cobalt and other metals, which has made it a global hotspot for mining prospecting.
How many protected areas are there in the Clarion Clipperton Zone?
The International Seabed Authority has set aside 13 no-mining reserves, called Areas of Particular Environmental Interest, covering nearly two million square kilometres.
What did the Plymouth Marine Laboratory study find?
Modelled larvae typically travelled less than 100 kilometres, while the reserves are 200 to 800 kilometres apart, so fewer than two in every 10,000 simulated larvae reached another reserve. Adding a small number of extra sites linked every reserve into one network and increased simulated larval exchange more than 400-fold.
Where was the deep-sea protected areas study published?
The study, titled Dispersal corridors enhance modelled near-bed larval connectivity across deep-sea protected area networks, was published in Nature Ecology & Evolution.
What are the limitations of the study?
The models simulate the physical possibility of dispersal driven by near-seabed currents rather than proving that populations exchange genes or recover this way in practice. The researchers said fieldwork, including direct current measurements and genetic sampling, is needed to test this.
