Scientists exploring deep-sea seeps, where methane bubbles up out of the seafloor, have made a discovery that changes our understanding of these mysterious ecosystems. They found that two species of tube worms actually trap methane, a powerful greenhouse gas, through a never-before-seen symbiotic relationship between the worms and methane-eating bacteria.

By mapping the seafloor near Costa Rica with autonomous underwater vehicles, the scientists also realized that these worms were spread out up to 300 meters farther away from the methane seeps than other organisms. Their research, published today in the journal Science Advances, could bolster arguments to expand the boundaries used to protect ecosystems around methane seeps from deep-sea drilling and mining. 

“It’s really important for the health of the earth, these ecosystems. Literally every time we are in the deep sea with a submersible and collecting things we discover a new species,” says Shana Goffredi, a lead author of the study and biologist at Occidental College. “There’s so much down there that we don’t yet know about and it would be a shame to lose them.”

What first caught the researchers’ attention was that the tube worms in this particular location — a methane seep called Jaco Scar — had a “more sort of fluffy appearance,” according to Goffredi. Sometimes when animals team up with bacteria living on their bodies, they can look “fluffy” or “hairy,” Goffredi explained. Until now, bacteria that feed off the methane spewing out of these seeps hadn’t been known to live on the bodies of ocean-dwelling invertebrates like the worms. She and her colleagues brought the worms up to their ships and discovered that the two species had figured out how to farm the bacteria living on their bodies as a source of nutrition.

“It’s like having your own kind of photosynthesis, but instead of using light energy they’re using methane as the energy source,” says Victoria Orphan, a co-author and geobiologist at the California Institute of Technology. The process breaks down the methane, keeping it from eventually rising up into the atmosphere. “It’s a really smart strategy for animals in these environments to team up with microorganisms because they are really the champion chemists in these habitats,” she says. Orphan and Goffredi believe similar worms surrounding methane seeps across the world are likely doing the same thing.

The life surrounding these seeps keeps up to 90 percent of the methane leaking out of the seafloor from eventually reaching the atmosphere and heating up our planet, according to some estimates. It’s still unclear how much of a role these worms play compared to free-living bacteria known to prevent much of the greenhouse gas from escaping the ocean. But the researchers stress that damaging these ecosystems through deep-sea mining and drilling before fully understanding them could have far-reaching effects. 

“A lot of these systems, just like the Amazon, are poorly understood and we’re still learning about the value of these resources. Our scientists are kind of in this race to at least establish a baseline to better inform conservation efforts,” says Orphan. “Even though [this ecosystem is] remote, that doesn’t necessarily mean that there isn’t a connection to us.”