Worms on the Seafloor That Gobble up Methane Through Their Skin Discovered

Tube-dwelling worms found at the seafloor have been found to act as a methane sink, getting nutrients from bacteria that use the gas as a source of energy. Researchers discovered the worms have an unusual symbiotic relationship with the bacteria, allowing it to cling to their skin and burrow into its tissues.

Only a handful of animals are known to associate with methane-oxidizing bacteria, which act as a biological sink for methane—a potent greenhouse gas—playing a role in limiting its release, and mitigating global warming. Discovering another species that interacts with methane-oxidizing bacteria potentially provides a new insight into the role seafloor creatures play in limiting climate change.

Methane seeps—where methane escapes trapped in the rock below escapes into the ocean—are found across the world. Much of the methane comes from buried organic carbon that has fallen to the bottom of the sea. These seeps provide a source of food for specialized microorganisms that have evolved to consume the gas. They are also an important source of methane to the environment and play a big role in Earth's carbon cycle.

In a study published by Science Advances, researchers led by Shana Goffredi, from the Occidental College in Los Angeles, studied these organisms found at a seep off the west coast of Costa Rica. Here lies a "vast series of seeps," with one found almost every 2.5 miles.

"Because of their unique community structure and significant cycling of carbon, sulfur, and nitrogen, it is increasingly important to understand the trophic interactions between these ubiquitous seep ecosystems and the chemosynthetic animals that they support," the team wrote.

Researchers were looking at two species of tubeworm found in these habitats. Previously, these species were thought to have got nutrients through suspension-feeding, consuming minerals suspended in the water. In their tests, however, the team found the worms were part of a symbiotic relationship with the methane-eating bacteria Methylococcales. They discovered the bacteria clung to the worm skin and burrowed in.

methane worms
Methane-consuming worms found on the seafloor off the west coast of Costa Rica. Alvin, WHOI

"Methanotrophs were not only attached to the epidermal surface of the worms but appeared to be in the process of engulfment by host tissue," the team wrote. "Bacterial cells...appeared deep in the worm tissues, surrounded by intracellular structures interpreted as digestive vacuoles."

Experiments with samples taken from the site showed the bacteria/worm combination were processing methane. The worms, they say, get nutrients from the methane in the bacteria—making them a previously unknown carbon sink.

The range these worms covered was found to be huge, with both species found almost 1,000 feet further away from the methane seep than other organisms. The authors say the findings should be taken into account when considering deep-sea conservation: "These newly discovered methane-reliant animals are commonly found at seeps and vents worldwide and extend the boundaries of the 'seep' habitat classification that is increasingly important for regulatory and stewardship efforts concerning fisheries and oil drilling in the deep sea," they conclude.

John Priscu, from Montana State University, who was not involved in the research, said that while some methane is consumed by bacteria, much ends up in the atmosphere where it acts as a greenhouse gas, warming the planet. The methanotrophic bacteria can act as biofilters for methane reducing its flux to the atmospheric methane pool, while at the same time providing new organic carbon to the environment in which they live, he told Newsweek.

"I see the results of this seminal study as opening new doors into our understanding of biologically mediated methane dynamics on our planet and in particular the role of microorganisms as a biofilter for atmospheric methane."

John Pohlman, a research chemist at the U.S. Geological Survey, who was also not involved, told Newsweek: "Based on my experience of studying ecosystems within karst subterranean estuaries that depend on methane as a form of nutrition, these are very interesting findings. This form of symbiosis, where the host maintains the methane-consuming symbiont externally and then digests it, is a relationship I am unfamiliar with for marine invertebrates.

"To my knowledge, these kind of symbiont-engulfing worms are more widespread around deep-ocean seeps than other seep-associated organisms and the nature of how they acquire nutrients through that symbiosis would extend the known habitat for seep ecosystems and our appreciation for how methane supports deep-sea ecosystems."