Japan – A groundbreaking study has uncovered astonishing biodiversity in the deepest ocean trenches of Japan, the Ryukyu, and Izu-Ogasawara regions, reaching nearly 10 kilometers below the surface. The research documented at least 108 distinct organism groups and included the deepest-ever sighting of a fish, alongside an unidentified “mystery” species that has baffled global experts.

Conducted over two months in 2022 aboard the vessel DSSV Pressure Drop, the expedition involved scientists from the Minderoo-UWA Deep-Sea Research Centre and Tokyo University of Marine Science and Technology, funded by Caladan Oceanic LLC and Inkfish.

Instead of traditional trawling, which can harm fragile organisms, the team used crewed submersible transects and free-fall baited landers. This dual approach allowed researchers to study seafloor animals in their natural habitats and capture bait-attending fauna such as fish and decapods.

Among the most mysterious findings was a slow-gliding animal, tentatively named Animalia incerta sedis, filmed at 9,137 meters. Experts have been unable to assign it to any known phylum. While it shows some resemblance to nudibranchs or sea cucumbers, its classification remains a mystery.

Submersible transects also revealed dense “crinoid meadows” with over 1,500 stalked crinoids and carnivorous sponges of the Cladorhizidae family at depths of 9,568 to 9,744 meters, the deepest recorded for these sponges.

Baited landers captured a snailfish feeding at 8,336 meters, setting a new depth record for fish, and documented the massive scavenging amphipod Alicella gigantea across all trenches. Researchers noted that while some species are widespread, each trench shows unique patterns shaped by geology, depth, and nutrient inputs.

The study also highlighted human impact, detecting debris likely carried by downslope processes. The team emphasized that non-destructive visual surveys are vital for understanding deep-sea ecosystems and providing a foundation for future research.

“This study was not simply about observing deep-sea organisms, but also aimed to establish a foundation for future research at these depths. More than anything, the hadal zone remains one of Earth’s least-explored and most intriguing frontiers,” the researchers concluded.

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