On 30 July 2025, a team from the Institute of Deep-sea Science and Engineering (IDSSE) at the Chinese Academy of Sciences published a paper in Nature reporting communities of tubeworms and clams living on the floor of two Pacific trenches at depths down to 9,533 metres. That is close to six miles beneath the surface, in the hadal zone, where no light reaches and photosynthesis is impossible. The paper, Flourishing chemosynthetic life at the greatest depths of hadal trenches, describes the deepest animal communities yet recorded, and the most extensive chemosynthesis-based ecosystem found anywhere on Earth.
The observations were made from Fendouzhe (Striver), China’s crewed full-ocean-depth submersible, operating from the research vessel Tansuoyihao. According to the paper, the team surveyed the trench floors between 8 July and 17 August 2024, in the Kuril–Kamchatka Trench and the western Aleutian Trench, the stretch of deep ocean that runs between the Russian Far East and Alaska.
What the submersible actually found
The communities are dominated by two groups of animals: siboglinid polychaetes, the family that includes deep-sea tubeworms, and bivalves, the group that includes clams. In the footage released with the study, the tubeworms grow in dense fields, some reaching around 30 centimetres, their exposed plumes coloured deep red by haemoglobin. The clams cluster in white beds across the sediment. None of it looks like what most people picture at the bottom of a trench, which is usually described as sparse, slow, and reliant on scraps falling from far above.
The scale is the part that is hard to overstate without overstating it. The paper reports that these communities span roughly 2,500 kilometres along the trench floors, at depths from about 5,800 metres to 9,533 metres. That is not a single seep or a lucky patch. It is a distribution long enough to reach from one end of a continent to the other, sitting in one of the least accessible environments on the planet.
Life without sunlight
These animals do not eat, in the ordinary sense. They rely on chemosynthesis, a process in which bacteria, rather than plants, sit at the base of the food web. The tubeworms and clams host symbiotic bacteria in their tissues. Those bacteria draw energy from chemical reactions involving methane and hydrogen sulphide seeping from the seafloor, and use it to build organic matter from inorganic carbon. The host animal lives on what its resident bacteria produce.
Chemosynthetic communities are not new to science. They have been studied at hydrothermal vents and cold seeps since the late 1970s. What is new here is the depth, the extent, and the source of the chemicals. According to the IDSSE team, the methane and hydrogen sulphide are carried upward along faults in the trench floor, and geochemical analysis points to the methane being microbial in origin, produced by microbes breaking down organic matter buried in deeper sediment layers. That detail matters, because it implies an active community of life beneath the seafloor feeding the community on top of it.
Why this changes the depth record
Before this expedition, chemosynthetic communities in the hadal zone were known only from scattered observations. The announcement from the National Natural Science Foundation of China, which co-funded the work, notes that the previous deepest record came from the Japan Trench at 7,434 metres, and that hadal sightings had been sporadic rather than continuous. The new observations push the confirmed depth down by more than two kilometres and, more importantly, replace a handful of isolated sightings with a picture of communities distributed across a long section of trench.
The researchers frame this as evidence for what they call a “Chemosynthetic Life Corridor” running through the world’s deep trenches. It is worth being precise about what that phrase is doing. It is a hypothesis drawn from a large but still single body of observations along two connected trenches. It is not yet a demonstrated feature of every trench on Earth. The paper supports the claim that these communities are far more widespread at extreme depth than previously assumed. It does not establish that they line every hadal trench, and the authors do not claim that.
What it means for the carbon question
The finding also touches the deep-sea carbon cycle. The long-standing view has been that hadal ecosystems run mostly on organic particles drifting down from surface waters, the slow rain of dead material from the sunlit ocean above. These communities complicate that view by showing that chemically fuelled life can be a substantial presence at the very bottom, drawing on carbon stored in the sediment rather than carbon delivered from above. How much that shifts the overall accounting of carbon in the deep ocean is an open question, and one the paper raises rather than settles.
There is a national dimension worth naming plainly. This is a Chinese-led result, funded under China’s National Key R&D Programme and carried out with domestically built deep-sea hardware. Full-ocean-depth crewed diving is a capability only a few countries hold, and the ability to return to the same trench floors repeatedly is what made a survey on this scale possible. The science and the platform are hard to separate here.
What to watch next
The immediate open questions are about breadth and mechanism. Do comparable communities exist in the other major trenches, as the corridor hypothesis predicts, or are the Kuril–Kamchatka and Aleutian systems unusual in the way their faults deliver methane and hydrogen sulphide? How large is the sub-seafloor microbial community implied by the methane’s microbial signature, and how much carbon does it actually process? Answering either will take more dives, more sampling, and probably more than one national programme working the deep trenches. For now, the record for the deepest known animal ecosystem sits at 9,533 metres, on a trench floor between Russia and Alaska, sustained by chemistry rather than sunlight.
