According to a study published in the prestigious journal Nature, this marks the deepest animal colony ever observed on Earth. The findings challenge long-held assumptions about the limits of life in the deep ocean and shed new light on the mysterious, extreme environments known as hadal trenches.
The expedition, which utilized the manned submersible Fendouzhe as part of a joint mission exploring the Kuril–Kamchatka Trench and the western Aleutian Trench, revealed that complex animal life is not only present in these crushing depths but can flourish on a massive scale.
“Hadal trenches, some of the Earth’s least explored and understood environments, have long been proposed to harbour chemosynthesis-based communities. Despite increasing attention, actual documentation of such communities has been exceptionally rare,” the study’s authors wrote in their findings. “Here we report the discovery of the deepest and the most extensive chemosynthesis-based communities known to exist on Earth during an expedition to the Kuril–Kamchatka Trench and the western Aleutian Trench using the manned submersible Fendouzhe.”
The Mariana Trench, situated in the western Pacific Ocean, plunges to depths that extend farther than the height of Mount Everest. For decades, scientists viewed these deep-sea valleys as barren, desolate landscapes due to the complete absence of sunlight, near-freezing temperatures, and immense hydrostatic pressure. However, this latest discovery suggests that life may be far more resilient and widespread in the ocean’s deepest trenches than previously anticipated.
“Given geological similarities with other hadal trenches, such chemosynthesis-based communities might be more widespread than previously anticipated,” said lead author Xiatong Peng, as reported by Oceanographic.
The newly identified communities primarily consist of siboglinid polychaetes—commonly known as tubeworms—and bivalves, spanning an astonishing distance of 1,553.4 miles at depths ranging from 3.6 to 5.92 miles below the surface.
Because no sunlight penetrates the ocean at these extreme depths, the creatures cannot rely on photosynthesis to generate nutrients. Instead, they subsist entirely through chemosynthesis, a biological process where organisms convert chemical energy into food.
The researchers noted that these thriving colonies are sustained by hydrogen sulfide-rich and methane-rich fluids. These chemical-laden fluids are transported along active faults traversing deep sediment layers within the trenches. Isotopic analysis conducted by the research team indicated that the methane powering the ecosystem is produced microbially from organic matter that has drifted down from upper layers of the ocean over vast periods of time.
“These communities are sustained by hydrogen sulfide-rich and methane-rich fluids that are transported along faults traversing deep sediment layers in trenches, where methane is produced microbially from deposited organic matter, as indicated by isotopic analysis,” the study’s authors explained.
Scientists emphasize that these findings fundamentally challenge current models of deep-ocean carbon cycling and push the boundaries of where life can successfully adapt and multiply.
During its expeditionary dives last year, the Fendouzhe submersible descended into the Mariana Trench 23 times. Throughout these dives, the scientific team captured stunning visual documentation of dense benthic communities that defied expectations.
“What makes our discovery groundbreaking is not just its greater depth—it’s the astonishing abundance and diversity of chemosynthetic life we observed,” said study co-author Mengran Du, a marine geochemist with the Institute of Deep-sea Science and Engineering, part of the Chinese Academy of Sciences, in an interview with Reuters. “Unlike isolated pockets of organisms, this community thrives like a vibrant oasis in the vast desert of the deep sea.”
Video footage released alongside the scientific study revealed expansive fields of tubeworms growing up to a foot long, alongside massive clusters and mounds of clams and various mollusks. Researchers also documented free-floating marine worms, spiky crustaceans, sea lilies, sea cucumbers, and a host of other unidentified invertebrates navigating the abyssal floor.
Furthermore, the team gathered compelling evidence indicating that active microbes were continually producing methane in the sediment, with tubeworms showing a distinct biological tendency to cluster closely around snow-like microbial mats.
While previous scientific expeditions had successfully identified communities of single-cell organisms thriving on the deepest seafloors, encounters with larger, complex animals at these scales have been exceedingly rare. Prior to this discovery, remotely operated vehicles had occasionally spotted marine invertebrates, such as tubeworms, living inside hydrothermal vents located 1.24 miles below the floor of the Pacific Ocean within the Earth’s crust. Finding such a vast, sprawling ecosystem at nearly six miles depth represents a dramatic leap forward in marine biology.
The publication of these findings arrives at a critical global juncture, as international policymakers and scientists debate the controversial expansion of deep-sea mining for valuable minerals. Ocean conservationists and marine scientists have repeatedly warned that commercial industrial activities on the fragile, little-explored ocean floor could permanently devastate unique marine ecosystems in one of the last truly wild and pristine frontiers on the planet. Despite ongoing talks, the International Seabed Authority has yet to adopt comprehensive binding rules governing the nascent deep-sea mining industry.
Human exploration of the Mariana Trench remains a historic and exclusive milestone. Though the first explorers briefly touched down at the bottom of the crescent-shaped trench during a daring 1960 expedition, only a handful of human beings have ever witnessed the environment firsthand. Among them is Hollywood director James Cameron, who completed a historic solo descent in 2012, famously describing the alien landscape as desolate and stark.
For modern researchers like Mengran Du, viewing these deep-sea realms from the viewport of a submersible remains an awe-inspiring and humbling scientific endeavor.
“Diving in the submersible was an extraordinary experience—like traveling through time. Each descent transported me to a new deep-sea realm, as if unveiling a hidden world and unraveling its mysteries,” Du said, reflecting on the arduous dives that led to the historic discovery.
The complete research paper, titled “Flourishing chemosynthetic life at the greatest depths of hadal trenches,” is now available to the scientific community in the journal Nature.
