Polymetallic nodules stud the seafloor throughout the Clarion-Clipperton Zone, and new research shows that each of these strange metal potatoes contains an entire community of microscopic life unique to this habitat.
There’s a reason humans have named them polymetallic nodules: we’re really interested in the metal part.
Our society’s reliance on metals like nickel, cobalt, and copper is growing rapidly, and these nodules are loaded with them, as well as iron and manganese.
But polymetallic nodules are not a readily renewable resource. Though it only takes minutes to pluck a nodule from the seafloor, it took millions of years for it to form.
Scientists are concerned this speculative industry could destroy a unique ecosystem we barely knew existed, before we get a chance to understand it.
“Our findings point out that commercial mining may result in an irreversible loss of undescribed and unique biodiversity associated to nodules,” says deep-sea biologist Sabine Gollner, of the Royal Netherlands Institute for Sea Research.
“This needs to be considered in environmental management of deep-sea mining.”
The research is published in Scientific Reports.
The nodules were collected in 2019 by a crew of scientists taking part in an expedition to the Clarion-Clipperton Zone aboard the German research vessel RV Sonne, as part of the JPI Oceans Mining Impact II project.
The team carefully lowered a box corer to depths of around 4 to 6 kilometers (2.5 to 3.7 miles) to take a chunk of seafloor sediment and the nodules embedded within.
For this study, the researchers examined 244 individual nodules looking for signs of life in the cracks and pores.
The nodules – and their marine inhabitants – were then frozen and taken to a lab.
One hundred fifty-three of the nodules came from an area where Germany’s Federal Institute for Geosciences and Natural Resources (BGR) holds an exploration contract from the International Seabed Authority. A further 91 were collected from an area where Belgian company Global Sea Mineral Resources – a subsidiary of DEME – holds an exploration contract.
Most assessments of biodiversity in the Clarion-Clipperton Zone so far have focused on organisms living in the sediment, or clinging to the nodules’ surface.
Much of the deep sea is covered in a fine mud, but many of the animals that live there need a more solid surface to attach to: the polymetallic nodules provide an ideal substrate for those creatures.
“We already knew that polymetallic nodules provide attachment surfaces for deep-sea organisms, but very little was known about the animals living inside them,” marine genomicist Coral Diaz-Recio Lorenzo told ScienceAlert.
On cracking the nodules open, scientists found bustling ecosystems in miniature throughout the nooks and crannies.
Roundworms and crustaceans were the most common inhabitants, and one species of ‘armored amoeba‘, Thurammina, dominated its kind. In just a few nodules, they recorded bristleworms, mud dragons, tardigrades, and other less common critters.
“What surprised us most was how different the communities living inside nodules were from those in nearby sediments,” Diaz-Recio Lorenzo said.
“Remarkably, nodule communities collected from areas separated by approximately 1,000 kilometers were more similar to one another than to the surrounding sediment communities.”
Using microscopes to look more closely at the nodules, the researchers also found the fossils of diatoms, radiolarians, and sea sponges embedded within the ancient layers.
“The presence of… biogenic particles within crevices indicated that at least some cavity structures were colonized by ancient organisms, although this does not necessarily demonstrate in-situ colonization at the time of incorporation,” the team writes.
“Sponge spicules were visible in the [scanning electron microscope] images, and the presence of the Foraminifera species Saccorhiza sp., which uses sponge spicules to build its tests [shell-like structures], indicates that nodules may have provided a habitat on the seabed for millions of years.”
If the ISA grants approval for deep-sea mining companies to take the nodules en masse, these ancient ecosystems will be irreversibly destroyed.
“Because their communities differ from those in the surrounding sediments, protecting sediment habitats alone would not preserve this biodiversity,” Diaz-Recio Lorenzo added.
“Large-scale nodule removal could therefore result in irreversible losses of unique species and ecological communities that we are only beginning to understand.”
These distant and microscopic worlds may seem quite isolated from ours, but the reality is we have no idea yet how they play into global networks of nutrients, carbon, and ecology.
Scientists are in a race to figure that out, before it’s too late.
The research has been published in Scientific Reports.
This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
