An international team has captured footage of 29,556 animals in Japan’s deepest ocean trenches, revealing how life survives in darkness and extreme pressure. Using a full ocean-depth submersible, researchers explored three trenches—the Japan, Ryukyu, and Izu Ogasawara—filming the seafloor in unprecedented detail.
The study was led by Dr. Denise Swanborn, a deep-sea ecologist at The University of Western Australia’s Minderoo Deep Sea Research Center (MDSR). Her work focuses on how the deepest ocean communities respond to changing food supplies and physical disturbances. The hadal zone, deeper than 20,000 feet, hosts unique communities under pressures more than a thousand times that at sea level, and temperatures just above freezing.
Researchers used a crewed submersible to survey depths between 23,000 and 32,000 feet, recording animals across sediment and rocky habitats. They identified 70 morphotypes across 11 major animal groups and categorized eight habitat types, from flat muddy plains to steep rocky slopes.
Food supply played a key role in shaping these communities. Particulate organic carbon—tiny particles of dead plankton and waste—falls from surface waters to the seafloor. Trenches under productive surface waters received more particles, supporting denser populations and more deposit feeders. Filter-feeding animals stretched tentacles to capture drifting particles, while burrowing worms and sea cucumbers processed settled sediment.
Tectonic activity also affects trench ecosystems. Earthquakes and underwater landslides periodically reshape the seafloor. Following the 2011 Tohoku Oki earthquake, muddy flows buried animals and redistributed sediment in the Japan Trench. “Within trenches, at the same depth band, differences in historical seismic disturbance and seafloor stability created different communities,” Dr. Swanborn said.
Species distributions varied among trenches. The Japan Trench hosted swarms of mysid shrimps and sea cucumbers on muddy areas; brittle stars dominated the Ryukyu Trench; and the Izu Ogasawara Trench contained stalked crinoids anchored to rock. Farther south, thickets of carnivorous cladorhizid sponges and roaming sea cucumbers were observed. Such findings suggest that specific combinations of hard surfaces and water flow can create deep-sea hotspots.
Hadal trenches are crucial for storing sinking organic matter, locking away carbon that might otherwise recycle in the water column. Understanding which habitats host the most diverse communities helps scientists estimate the ecological value of these carbon sinks.
“These discoveries in Japan’s trenches provide a guide for exploring other deep-ocean regions, where food supply and disturbance may interact differently,” Dr. Swanborn added.
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Related video: Deep Sea Trenches Exploration – YouTube
