A metal treasure hides at the bottom of the ocean. Potato-sized nodules of iron and manganese litter the seafloor, and metal-rich crusts cover underwater mountains and vents along hydrothermal vents. Deep-sea mining companies have set their sights on these minerals, aiming to use them in batteries and electronics. Environmentalists warn that the mining process and the plumes of sediment it would release into the sea could affect marine life.
A series of shipboard experiments on jellyfish in Norwegian fjords, published Tuesday in the journal Nature Communications, offer insight into these warnings. Scientists estimated the effects of mining by pumping sediment into the jellies’ reservoirs, essentially wondering how animals would respond to the muddy water. The answer? Not good.
Researchers chose helmet jellyfish as research subjects because of the ubiquity and robustness of these dinner plate-sized creatures. The idea was to choose an organism that the team could easily get their hands on “and then expose it to the conditions we expect in mid-waters in the open ocean,” said Helena Hauss, a marine ecologist at the Research Center. Norwegian who conducted a study. the study while working at the GEOMAR Helmholtz Center for Ocean Research in Kiel, Germany.
The jellies, found around the world in waters 1,500 to 2,000 feet deep, are representative of the countless soft-bodied animals living in the deep sea that could be affected by mining.
The scientists captured the jellyfish, which are abundant in Norwegian fjords, with fine-mesh nets and brought them below the deck of their research vessel to study them in dark rooms lit by red light.
“They are really adapted to live in eternal darkness,” said Vanessa Stenvers, author of the paper and a doctoral student at GEOMAR. “And that’s why we had to be very careful when we observed and we always had to use the red light so as not to disturb them.”
The scientists exposed the jellies to plumes of sediment comparable to those they might encounter around deep-sea mining sites. A response from the jellyfish was visible to the naked eye. They tried to get rid of the sediment by producing excess mucus, in the form of white strings that Ms Stenvers likened to icing.
Other stress responses occurred at the molecular level, with several genes associated with tissue repair and the immune system becoming active.
“One thing that worries me is that everything these animals do to get rid of sediment or fight pathogens takes energy,” Dr. Hauss said. In the depths of the ocean where jellyfish live, food is scarce and coping with the effects of muddy water can require more energy than the jellyfish can get from their diet. “It could lead to starvation, it could lead to lower reproductive rates,” Dr. Hauss said.
Jeffrey Drazen, a marine biologist at the University of Hawaii at Manoa who was not involved in the research, said “this is a really welcome study” given the likelihood that deep-sea mining will release large quantities of sediment. “This is truly the first study to look at how an animal living in the water column responds to mud,” he said.
Dr. Drazen noted that the species the researchers chose for the study was more resilient than many of its related species. “It’s a really hardy jellyfish. You can catch this thing in a net and it doesn’t turn into a goo,” he said, and its response to sediment stress indicates that other soft-bodied marine creatures exposed to sediment for longer periods periods could fare even worse.
According to the researchers, their results suggest that deep-sea mining could have a negative impact not only on marine life, but also on human life. Mid-ocean animals, like helmet jellyfish, contribute to a biological cycle that maintains carbon stores in the depths and not in the atmosphere. And the fish that humans depend on for food, like tuna, feed on these mid-ocean communities.
“It’s very important to us, even on earth, even though we don’t face it every day,” Ms. Stenvers said. The good that the ocean brings to our planet “could be lost if we don’t protect it.”