5,000 new animal species described living in dark ocean depths near Mexico, United States

About 5,000 new species – and likely more – have been discovered living off the coast of Mexico, potentially raising concerns for a deep-sea mining industry looking to extract metal-rich materials from the ocean floor.

One hotspot for deep-sea mining is the Clarion-Clipperton Zone (CCZ) – six million square kilometres of ocean between Mexico and Hawaii, which has been identified as a site of polymetallic nodules containing a range of important elements like cobalt and nickel.

The International Seabed Authority (ISA) is under pressure to allow deep seafloor mining in international waters when it meets in July.

But now, a British and European team has, for the first time, published a checklist of 5,142 new species: around a quarter are arthropods (which include crustaceans), and a third are worm species.

Echinoderms like starfish, sea urchins and cucumbers, and coral species were also described.

These species were among more than 100,000 individual records analysed from research surveys in the CCZ, collected using remote-control vehicles or sturdy boxes to scoop the creatures from the seafloor.

When pulled up from the deep, records were uploaded to the ISA’s DeepData platform – a public listing of biological, physical and geochemical information of deep ocean ecosystems.

This allowed the UK Natural History Museum’s deep-sea research group data manager Muriel Rabone and colleagues to identify the massive number of previously unnamed species.

‘Right here on the ocean floor, such wonderful things’

Just as Sebastian the hermit crab sings in the line from The Little Mermaid, Earth’s ocean floor is an amazing place.

“Time moves on a different plane of existence, in a way,” Rabone says.

That’s because the unusual animals of the abyssal depths reside 3,800 to 5,500 metres below the surface. This exposes them to virtually no light – it’s a world bathed in darkness – high pressure and temperatures only just above freezing point.

Rabone likens the undersea geography of the CCZ to the hilly regions of her native New Zealand – akin to a mountain range under the sea.

“There are two fracture zones that may act as biogeographic barriers – a cliff for example. There are cliffs, there are shelves, there are rocky outcrops, there are areas with nodule cover, areas with no nodule cover at all,” she says.

“I don’t think that it can be underestimated, how highly variable the habitat is, which is one of the reasons that’s contributing to this high biodiversity in the area.”

There are almost certainly more undiscovered and undescribed species lurking in the darkness of these deep waters, with the researchers projecting more than 6,000 species, and potentially upward of 8,000 in the region.

But it isn’t just the biological discoveries captivating scientists in the CCZ.

Protecting deep diversity amid drive for metal

So-called nodules are stone-like aggregations of metal that have formed over millions of years on the seafloor.

They’re of particular interest because they promise unparalleled access to deposits of essential metals that can be held in one’s hand. Such metals could be used in manufacturing important products like batteries to drive the global green energy transition.

But nodules also have important biological functions: in some cases, they provide animal habitat.

Undersea nodule mining might have a radioactive problem

And understanding the huge biodiversity of the CCZ raises the question of how animal life will be protected in this untouched region of the planet.

Maintaining undisturbed lives until the advent of deep-sea exploration in the 1800s, the species and ecosystems that have since been discovered in the world’s deep-sea regions are important candidates for further study, which may be compromised by mining.

“Life evolved in the seas. There’s really deep basal level diversity in the sea, [and] a huge amount of adaptation to these pressures and this depth, and lack of light,” Rabone says.

“The nodules are a really interesting question… from a biological perspective, it’s incredibly interesting because every single nodule looks different: they have particular kinds of sizes of shapes, and it would be really interesting to see how they’re colonised.

“You get the odd nodule with a really big animal growing on it, and literally every single nodule has little animals on it.

“Some nodules have close to nothing, or were actually barren, but they would have still had some bacteria or some tiny animals.”

The ISA is due to finalise its international regulations for deep seabed mining in July this year.