The deepest garden on Earth: Chinese scientists discover 32 thriving species in the world's deepest ocean trenches

The hadal zone takes its name from Hades, the Greek god of the underworld, and for good reason. Stretching from roughly 4.7 to 6.8 miles below the ocean surface, it is one of the most hostile environments on Earth, perpetually dark, crushingly pressured, near-freezing, and almost entirely cut off from the sunlight-driven food chains that sustain most life. For a long time, scientists assumed it was largely barren. A team of Chinese researchers has now dismantled that assumption strikingly, discovering a dense, previously undocumented ecosystem of 32 species thriving on hard rock surfaces across multiple Pacific Ocean trenches at depths that were once considered incompatible with complex life.The hadal zone encompasses the deepest regions of the ocean, primarily the narrow, V-shaped trenches formed at tectonic subduction zones and makes up only a small fraction of the ocean floor by area. Despite its physical extremity, it sits at the bottom of every ocean food web as the ultimate destination for organic material sinking from above. According to NOAA's Ocean Exploration programme, the hadal zone remains one of the least explored environments on the planet, with vast stretches never visited by any research vessel or submersible. The new research, published in the journal Science, represents the most comprehensive survey of hard-substrate life in this zone ever conducted.The work was carried out by researchers at the Institute of Deep-Sea Science and Engineering (IDSSE) of the Chinese Academy of Sciences, operating under the Global Hadal Exploration Program. Between 2020 and 2024, the team completed 98 dives using China's crewed deep-sea submersible Fendouzhe, known in English as Striver, which is capable of reaching depths exceeding 6.2 miles and can carry up to three crew members. The dives spanned seven hadal regions across the Pacific, including the Mariana Trench, the Kermadec Trench, and the Aleutian, Kuril-Kamchatka, Atacama, Puysegur, and Mussau trenches, a scale of coverage that no previous hadal survey had achieved.What the team found on the exposed rock surfaces of these trenches was not the sparse, scattered life forms that earlier research had occasionally recorded. It was something far more structured: dense colonies of millimetre-scale organisms clinging to vertical rock outcrops, forming what the researchers described as a garden-like hard-substrate ecosystem at depths ranging from 19,700 to 35,750 feet below sea level.The survey recorded a total of 32 species from six phyla, the broad biological groupings that include everything from molluscs to echinoderms, with the majority never previously described by science. Among the most significant discoveries were a new family of unilocular foraminifera, named Plumettidae, and a novel family of bryozoans called Pierrellidae. The dominant life forms across the surveyed trenches were agglutinated foraminifera, microscopic single-celled organisms that build their own shells from particles in their environment. These appeared in thread-like, tubular, and dome-shaped forms and had previously been difficult to classify due to their tiny size and structurally simple appearance. Genetic and metagenomic analysis finally confirmed their biological identity.The population densities recorded were remarkable. In the Kermadec Trench assemblages, the team measured up to 4,300 organisms per square decimetre, roughly equivalent to a hand-sized patch of rock. Professor Peng Xiaotong of IDSSE described the four dominant millimetre-scale species as the most unexpected element of the entire discovery. "The most unexpected components were four new and much smaller species that occurred in high densities and dominated the hard-substrate Kermadec Trench assemblages," he said.Perhaps the most surprising finding of the study concerns how these organisms actually survive. The prevailing hypothesis had been that hadal fauna at such depths would depend on chemosynthesis, the process by which organisms near hydrothermal vents derive energy from chemical reactions rather than sunlight. The new evidence overturns that idea. Inside the organisms, the researchers found partially digested pine pollen grains. The organisms are heterotrophs: they feed on organic debris drifting down from the surface world far above, effectively eating atmospheric dust that has settled into the ocean, been carried downward by water movement, and eventually reached the trench floor.The physical geometry of the trenches helps explain how this works. The V-shaped walls funnel organic matter downward and concentrate it, while powerful underwater sediment flows continuously scour the rock surfaces, keeping them clear of burial. The rock-feather organisms preferentially colonise vertical rocky outcrops precisely because the angle prevents sediment from covering them, while also positioning them to intercept nutrient particles carried upward by bottom currents. The ecosystem is, in this sense, architecturally dependent on the trench's own topography.The implications extend beyond biodiversity. The study suggests these sessile foraminifera could account for between two and eleven per cent of total eukaryotic biomass carbon in the hadal zone, a proportion large enough to make them a significant and previously unrecognised component of the deep-sea carbon cycle. "Our results suggest that hadal hard-substrate faunas form an important carbon pool," Professor Peng concluded. Given the role of the deep ocean in regulating long-term carbon sequestration, that finding has implications well beyond marine biology.The expedition also set new depth records for several marine groups, including the deepest-known bryozoan species at 32,746 feet and scyphozoan polyps at 32,749 feet. The fact that similar hard-substrate communities were observed across multiple trenches from the Mariana to the Atacama suggests this ecosystem is not a localised anomaly but a widespread feature of the hadal zone that has simply gone undetected until now. The world's deepest ocean floors, it turns out, are not empty. They are gardens.