Chemosynthesis-based animal communities are sustained by chemosynthetic microorganisms that harness the energy released during chemical reactions of compounds that seep from the sea floor. Since their initial discovery at hydrothermal vents, these communities have also been detected at cold seeps across a range of depths. Writing in Nature in July 2025, Peng et al. documented the deepest and most extensive chemosynthesis-based communities known to exist on Earth. This discovery was made during an expedition to the Kuril–Kamchatka Trench and Aleutian Trench in the northwest Pacific Ocean using a crewed submersible. Across both trenches at depths from 5,800 m to 9,533 m and spanning a distance of more than 2,500 km, the team observed dense cold-seep communities of chemosymbiotrophic siboglinid polychaetes and bivalves, alongside heterotrophic benthic fauna including free-moving polychaetes, gastropods, crinoids and amphipods. Isotope analyses suggested that considerable methane concentrations detected around the seeps result from microbial reduction of carbon dioxide derived from sedimentary organic matter. Overall, the findings imply that the chemosynthetic life in these trenches use methane-rich and hydrogen-sulfide-rich fluids as energy sources, transported along faults that traverse deep sediment layers in the trenches. This challenges the traditional view that hadal fauna rely predominantly on surface-derived organic matter and reveals a previously unknown contribution of chemosynthesis to the functioning of hadal ecosystems. We highlight this paper for our Year in Review because reporting these flourishing communities could lead to further discovery of unknown interactions between animals and microorganisms, as well as to questioning of assumptions about life at extreme limits.
Original reference: Nature 645, 679–685 (2025)
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