Mining the seafloor for valuable metals could send risky ripples through ocean food webs.
Tiny floating plankton, the base of the food web, can accidentally ingest particles of sediment kicked up by deep-sea mining operations — forgoing more nutritious food of similar size, researchers report November 6 in Nature Communications.That could trigger a bottom-up starvation cascade, even up to large marine predators, the team says.
Researchers have long feared that seabed mining could cause irreparable harm to deep-sea ecosystems.Equipment scraping the seafloor some 4,000 meters deep can disrupt fragile microbial communities in the sediment for decades. It can also kick up sediment plumes that can clog the filtration systems of bottom-dwelling creatures.
But shallower depths are also at risk: Seabed mining can release sediment plumes into the water at around 1,500 meters. The new study suggests these plumes may be deadly to plankton.
In 2021 and 2022,oceanographer Michael Dowd of the University of Hawaii at Mānoa in Honolulu and colleagues journeyed to the clarion-Clipperton Zone in the Pacific Ocean. There, the seafloor is littered with polymetallic nodules, chunks of rock enriched in metals such as cobalt, manganese and copper that are valuable for electronics.
During their first two trips, the team collected plankton and particles using giant nets deployed at depths between 800 and 1,500 meters. They analyzed the samples for particle size and chemical makeup — especially of the amino acids in the plankton and particles. By comparing the chemical forms, or isotopes, of nitrogen and carbon in those amino acids, the team determined that the plankton prefer to consume particles about 6 micrometers wide.
The team’s third trip was alongside a pilot deep-sea mining operation conducted by the Canada-based Metals Company. This time, the researchers collected samples of particles from within a waste plume of sediment created by the mining activities. Analyses of those particles revealed a distressing fact: They were similar in size to — but far less nutritious than — the food many plankton usually eat.
“[The plume particles] were basically junk food,” says study coauthor Brian Popp, a biogeochemist at the University of Hawaii at Mānoa. “They had very,very low protein content.”
That suggests a dangerous scenario, the team says, should deep-sea mining operations get under way in earnest: If more and more plankton are exposed to and consume these nutrient-poor particles, they might starve. and in turn, the creatures that feed on them would also suffer.
