A new deep ocean survey has captured more than 29,500 animals on video in some of Japan’s deepest and least explored trenches, offering a rare look at how life survives in near-freezing darkness under crushing pressure.
The work was led by Dr. Denise Swanborn of the University of Western Australia’s Minderoo Deep Sea Research Center, whose team used a full ocean depth submersible to film the seafloor between roughly 23,000 and 32,000 feet. The dives targeted the Japan, Ryukyu, and Izu Ogasawara trenches, a chain of extreme underwater gullies created by sinking tectonic plates.
Each dive recorded everything moving across sediment and rock while scientists later paused the footage frame by frame, identifying 29,556 animals. They organized them into 70 morphotypes spread across 11 major groups and mapped them onto eight habitat types that ranged from steep rocky walls to broad muddy plains.
Food supply proved to be one of the strongest drivers of life in the hadal zone. Trenches receiving more particulate organic carbon from the surface hosted denser communities and more deposit feeders, while leaner sites supported fewer animals. Even at similar depths, differences in surface productivity and ocean currents produced dramatically different communities.
Earthquakes also play a major role in shaping these habitats. Japan’s trenches sit along a seismically active region where underwater quakes and landslides frequently shuffle sediment. After events like the 2011 Tohoku Oki earthquake, mud flows can bury animals, redistribute organic matter, and reset entire stretches of seafloor. Swanborn noted that disturbed zones tended to host dense but low diversity communities, while stable slopes supported richer ecosystems.
The contrasts between trenches were striking. In the Japan Trench, thick carpets of sea cucumbers and swarms of mysid shrimp dominated muddy areas. The Ryukyu Trench hosted brittle stars instead. In the Izu Ogasawara Trench, the team found meadows of stalked crinoids anchored to hard rock and, in deeper sections, fields of carnivorous cladorhizid sponges.
Finding structured communities below about 29,500 feet is rare and suggests that the right mix of hard surfaces, flowing water, and steady organic input can create deep sea hotspots far below the reach of sunlight.
Hadal trenches store large amounts of sinking carbon, and mapping which habitats support the most life helps refine estimates of how these systems contribute to deep ocean carbon storage. Because full depth video surveys are uncommon, each expedition adds crucial data about how ecosystems function under extreme pressure.
The research appears in the Journal of Biogeography.