In a groundbreaking discovery off the central coast of Chile, an international team of scientists from Chile and the United States revealed that red cusk-eels, a commercially prized fish species, inhabit a methane seep ecosystem in unprecedented numbers. These fish, celebrated culturally and economically in Chile, were found sheltering within dense thickets of tubeworms at depths exceeding 400 meters. This revelation challenges previous assumptions about deep-sea methane seeps as habitat specialists and highlights their broader ecological importance for commercially significant marine species.
The methane seeps, characterized by the emission of methane and hydrogen sulfide from the seafloor, form unique chemical environments that host diverse and specialized ecosystems. Unlike photosynthetic food webs, these habitats rely on chemosynthetic bacteria capable of converting reduced compounds into organic matter, sustaining complex communities largely independent of sunlight. In this case, the tubeworms anchoring the methane seep mound thrive through symbiosis with these bacteria, creating a vast structural habitat that supports various organisms, including the red cusk-eel.
The red cusk-eel (Genypterus chilensis), often mistaken for a true eel due to its elongated body and undulating movement, is native to the southeastern Pacific Ocean, ranging from northern Peru to southern Chile. These fish typically dwell near the seafloor at depths of up to 350 meters but the discovery at 435 meters represents a deeper, less understood habitat utilization. Their presence in such methane seep environments raises compelling questions about the ecological function of these sites beyond their known microbial and invertebrate communities.
Prior to this study, the ecological role of methane seeps for commercially valuable fish species remained largely unexplored. Although some species like thornyhead rockfish on the United States’ West Coast and Chilean seabass (Patagonian toothfish) in the South Pacific have been associated with methane seeps, the documentation of red cusk-eels using these habitats expands the list and suggests that methane seeps may serve as critical refuges or feeding grounds for a wider array of fish than previously recognized.
The expedition, conducted aboard the Schmidt Ocean Institute’s Research Vessel Falkor (too) in October 2024, combined advanced shipboard sonar mapping with expert geological interpretations to identify potential methane seep sites. Researchers then deployed the remotely operated vehicle (ROV) SuBastian to investigate these mounds, capturing detailed imagery and observations at depths around 435 meters. It was during these dives that researchers observed a remarkable aggregation of 46 to 48 red cusk-eels nestled among the tubeworm bushes on a single methane seep mound located roughly 18 kilometers offshore from El Quisco.
One of the most striking aspects of these observations was the fish’s behavior within the tubeworm bushes. Videos show red cusk-eels swimming backward into the entangled tubes, presumably utilizing the intricate structures for shelter and possibly for protection from predators. Moreover, footage captured spider crabs appearing to clean parasites off the fish, suggesting a mutually beneficial relationship which may be integral in maintaining the health and survivability of the cusk-eels in this unique habitat.
The methane seep mound itself stood out due to the sheer size and density of tubeworm bushes carpeting its surface. Tubeworms attain their nutrition via endosymbiotic bacteria that exploit the chemical energy from methane seep fluids. These large aggregations form complex three-dimensional habitats on otherwise bare seafloors, offering shelter, hunting grounds, and breeding sites for a variety of species. The newly discovered congregation of red cusk-eels hints that such seeps can be biodiversity hotspots extending their ecological roles from microbes and invertebrates to commercially important fishes.
Importantly, surveys of eleven other nearby gas seep mounds revealed only three red cusk-eels in total, highlighting the unique suitability or attractiveness of this particular mound. The surrounding seafloor bore signs of fishing activity such as lost nets and debris, indicating human interaction with the site’s biological resources. This juxtaposition underscores the urgent need for conservation measures to protect methane seep habitats as potential nursery or refuge grounds for species threatened by overfishing.
Given that red cusk-eels are heavily fished along the Chilean coast—approximately 2,000 tons were landed in 2022, according to fisheries data—and research shows a high proportion of immature individuals being captured, the discovery of methane seep aggregations may have profound fisheries management implications. Protecting these sites could enhance stock resilience by preserving essential habitat for feeding, reproduction, or parasite avoidance.
The ecological connectivity illustrated by this new habitat use also challenges existing paradigms that have viewed methane seeps as isolated or marginal communities. Instead, these findings suggest substantial linkages between seep ecosystems and broader marine food webs, emphasizing that seep environments may serve critical functions for species with wide-ranging life histories, including those targeted by commercial fisheries.
Future research directions highlighted by the authors include determining whether the red cusk-eel congregations represent spawning aggregations, specialized feeding grounds, refuges from predators or environmental stressors, or parasite cleaning stations facilitated by symbiotic invertebrates. Long-term and seasonal monitoring will be crucial to understand the dynamics and ecological significance of these aggregations fully.
“This discovery happened within just two days of exploration,” says Lisa Levin, a veteran deep-sea ecologist and co-author of the study. “The potential for uncovering critical ecological interactions—and implications for conservation—are immense but largely untapped. Methane seeps continue to surprise us with their complexity and importance.”
Eulogio Soto, chief scientist and co-author from the University of Valparaíso, stresses the pressing need to return to these habitats to conduct extended studies: “The implications extend beyond ecology to fisheries sustainability and marine management. Protecting these unique environments amidst pressures from fishing and pollution must be prioritized.”
This study represents a timely addition to deep-sea ecology literature, emphasizing methane seeps as not only sites of microbial chemosynthesis but also pivotal habitats for a diverse assemblage of macrofauna including commercially important fish. As technological advances in deep-sea exploration continue, such discoveries will be integral in shaping marine conservation policies and sustainable fishery practices.
In sum, the congregation of red cusk-eels at this Chilean methane seep underscores the importance of previously underappreciated deep-sea ecosystems. It invites a reevaluation of marine habitat connectivity and the role of chemosynthetic ecosystems in supporting both biodiversity and human economies dependent on ocean resources.
Subject of Research:
Red cusk-eel (Genypterus chilensis) habitat use and ecology at deep-sea methane seeps
Article Title:
Congregation of cusk-eels (Genypterus chilensis, Ophidiiformes) at a deep-sea methane seep off Chile
News Publication Date:
18-Oct-2025
Web References:
http://dx.doi.org/10.1002/ecy.70237
https://schmidtocean.org/technology/robotic-platforms/4500-m-remotely-operated-vehicle-rov/
References:
Schmidt Ocean Institute research expedition, Ecology journal article DOI:10.1002/ecy.70237
Image Credits:
Schmidt Ocean Institute
Keywords:
Marine ecology, Deep sea mining, Methane seeps, Deep-sea fish ecology, Chemosynthesis, Red cusk-eel, Deep-sea biodiversity, Fisheries management, Tubeworm ecosystems
