MARUM Study Finds 4,139 Animals Living Inside Metal Nodules

Researchers analyzing 244 polymetallic nodules from the Clarion-Clipperton Zone have discovered a hidden ecosystem, finding an average of 17 microscopic animals living inside the crevices of each rock.

The study, led by an international team from the MARUM Center for Marine Environmental Sciences at the University of Bremen in Germany, reveals that these lumps of manganese and other metals are not merely static geological features but serve as a distinct, three-dimensional habitat for life.

The study, published in the journal Scientific Reports, identifies that these nodules provide a shelter for organisms smaller than a millimeter—creatures that are not found in the surrounding soft seafloor sediment.

The research team, which included experts from the Netherlands, Belgium, and France, documented a total of 4,139 individual animals within the samples. The communities are dominated by roundworms, known as nematodes, and small crustaceans called copepods, alongside other organisms such as polychaete worms, kinorhynchs, tardigrades, and the single-celled species Thurammina sp. 1.

“In our study we show that the sizes of cracks inside the nodules are large enough to provide home to animals that are smaller than a millimeter in size,” deep-sea ecologist and lead author Tanja Stratmann said.

The nodules were collected in 2019 by a crew of scientists aboard the German research vessel RV Sonne during an expedition to the Clarion-Clipperton Zone, an abyssal plain situated between Hawaii and Mexico. Using box corers at depths of 4,000 to 6,000 meters (2.5 to 3.7 miles), the researchers retrieved sediment and embedded nodules, which were subsequently dissected in a laboratory.

Coral Diaz-Recio Lorenzo, a postdoctoral researcher at Sorbonne University, noted: “The crevices in the polymetallic nodules function as small shelters and provide a home to animals that we do not encounter in the soft sediment of the seafloor.”

Microscopic analysis of the nodule interiors also revealed ancient traces of life, including microfossils of diatoms, radiolarians, and sea sponges. The presence of these structures suggests that the nodules have served as a habitat for millions of years, though the researchers clarified that the biogenic particles do not definitively prove the organisms lived there during the formation of the layers.

Polymetallic nodules are a target for industrial deep-sea mining due to the high concentration of metals such as nickel, cobalt, copper, and manganese. Because these nodules grow at an extremely slow rate—often just a few millimeters per million years—the researchers warn that their extraction would result in the loss of this unique ecosystem.

Professor Sabine Gollner of the Royal Netherlands Institute for Sea Research (NIOZ), who is also an honorary professor at the University of Groningen, emphasized the severity of this potential impact: “This needs to be considered in environmental management of deep-sea mining.”

The discovery comes as the deep-sea mining industry faces global debate. While 45 countries have called for a moratorium or a precautionary pause, a US subsidiary of The Metals Company (TMC) has applied for an exploration license and a commercial recovery permit. The company forecasts receiving a permit before the end of the first quarter of 2027, though NOAA must still finalize an environmental impact statement.

This path bypasses the International Seabed Authority (ISA), the United Nations-backed regulator that has faced repeated delays in establishing rules for commercial recovery. As the debate continues, the lead author of the study, Tanja Stratmann, is currently participating in a new expedition to the Clarion-Clipperton Zone to further investigate the extent of these microcommunities and determine if their loss could lead to broader ecological consequences.