A team of scientists from Chile and the United States discovered dozens of red cusk-eels, fish prized in Chilean seafood markets and celebrated in a poem by renowned Chilean poet Pablo Neruda , embedded in a bushy thicket of tubeworms at a methane seep off the coast of central Chile.
This is the first time this commercially important species has been documented using methane seeps as habitat. It's not yet clear what drew the fish to the methane seep, but some evidence suggests the fish may have been receiving a parasite cleaning from resident spider crabs.
"Methane seeps are important places for deep-sea biodiversity," said Lisa Levin, co-author of a study detailing the discovery and professor emeritus at UC San Diego's Scripps Institution of Oceanography. "Our findings show these seeps are not just home to communities of obscure creatures that are cut off from the rest of the deep sea. They are also important for commercially fished species and may be much more connected to the rest of the ocean than one might expect."
The discovery places the cusk-eels among a small but growing list of other commercially significant species using methane seeps. The study was published Oct. 18 in the journal Ecology . The research was supported by the Schmidt Ocean Institute and funded by the National Science Foundation.
Red cusk-eels (Genypterus chilensis) can reach lengths of 1.6 meters (five feet) and are usually found near the bottom at depths up to 350 meters (1,100 feet) from northern Peru to southern Chile. They are not true eels but their long slender body shape and undulating swimming style make it easy to understand how they got their name. In 2022, Chilean fishers hauled up roughly 2,000 tons of red cusk-eel (known locally as "congrio colorado"), and the fish features prominently in coastal restaurant menus. Research suggests the species is being overfished, with a 2003 study finding that 75% of the catch had not yet reached sexual maturity.
Methane seeps are where methane and hydrogen sulfide emerge from the seafloor. Thousands of these seeps have been discovered around the world, typically near continental margins. The seeps provide food for microbes that specialize in converting the leaking chemicals into energy through a process called chemosynthesis. These microbes form the base of thriving ecosystems that exist largely apart from the sun. Methane seeps have gained recognition as critical habitats for some species targeted by commercial fishing fleets, including thornyhead rockfish, Chilean seabass (also known as Patagonian toothfish) and deep-sea snow crabs.
An October 2024 oceanographic expedition aboard the Schmidt Ocean Institute's Research Vessel Falkor (too) set out to map and explore methane seeps off the coast of central and south Chile and to study the unique ecosystems they support.
The research team used a combination of shipboard sonar and expertise from collaborating geologists to locate mounds on the seafloor that were potential methane seeps. The team then deployed Schmidt Ocean Institute's ROV SuBastian to explore and film these sites.
The team discovered a large mound roughly 18 kilometers (11 miles) off the coast of El Quisco, a small town about 85 kilometers (53 miles) south of Valparaíso. On a dive to survey the mound some 435 meters (1,427 feet) below the surface, the team was impressed by the size and density of tubeworms attached to the mound's surface. Tubeworms, which flourish via a symbiotic relationship with the seep's chemosynthetic bacteria, form cylindrical tubes to protect their soft bodies, and large numbers of them create tangled bushes on the seafloor.
"At first we were amazed by the size of the tubeworm bush," said Levin. "Eventually we noticed all these fish with their heads poking out from inside the bush."
The team sent the ROV down to the mound twice over the course of two days and counted 46 to 48 red cusk-eels nestled within a large, dense tubeworm bush on this single mound. Researchers observed the fish swimming backwards into their hiding spots. Video also showed cusk-eels receiving what looked like a parasite cleaning from spider crabs that live in the tubeworm bushes. Levin said the fish could also be congregating to feed, reproduce or seek refuge.
"The presence of this important fishery resource on a methane seep ecosystem close to the coast where it faces pressure from fishing and pollution forces us to think about measures to protect and conserve these habitats," said Eulogio Soto, a researcher at the University of Valparaíso in Chile who served as a chief scientist of the expedition and co-authored the study. "Our discovery took place over the course of just two days, so we don't know what life exists or what is happening at other times of the year. We must go back."
The mound appeared to be singular in its appeal to the fish, with surveys of eleven other nearby mounds turning up only three fish in total. The surrounding seafloor near the methane seeps was littered with lost nets and other fishing gear, suggesting this location may be known to local fishers. The findings could inform the management of the red cusk-eel fishery, perhaps serving as the basis for protecting the site and others like it from fishing.
The study authors said future research should explore whether these aggregations represent spawning sites, feeding grounds, refuges or parasite cleaning stations.
"Almost every time we visit these ecosystems, we find something new," said Levin. "There is so much more for us to learn, and we need to keep exploring and studying them."
In addition to Levin and Soto, the study was co-authored by Yerko Castillo of the University of Valparaiso, Patricia Esquete from the University of Aveiro and Jeffrey Marlow of Boston University.
