Scientists from the University of Western Australia’s Minderoo Deep-Sea Research Centre and the Tokyo University of Marine Science and Technology have announced the discovery of a complex ecosystem of life forms living in the Japan, Ryukyu, and Izu-Ogasawara trenches nearly 10 kilometers (6.25 miles) beneath the ocean surface.
The research team behind the 2022 expedition, which was funded by Caladan Oceanic LLC and Inkfish, said the valuable discoveries included 108 distinct organism groups, and one “baffling, unidentified animal that has left global taxonomic experts stumped.”
Expeditions Film ‘Unique, Slow-Gliding’ Mystery Organism
According to a statement detailing the research, the 2022 expedition aboard the vessel DSSV Pressure Drop, which lasted two months, eschewed traditional research methods using trawls and physical sampling because these methods can damage fragile organisms and “rarely capture behavior.” Instead, the UWA-Minaroo-led team employed two hands-on methods.
The first approach involved crewed ‘transects’ of the selected area in submersibles, allowing researchers to study the animals that call the seafloor home and their habitats in a less invasive way. The second approach employed free-fall landers that were loaded with bait to target fish and more complex decapods that call the deep-sea trenches home.
“Historically, our understanding of abyssal and hadal ecosystems, including those associated with subduction features, relied largely on trawls and physical samples,” the research team explained. “While these methods provide essential information, they can damage fragile organisms and rarely capture behaviour or ecological context.”
The researchers said this dual approach resulted in the “most comprehensive visual baseline yet for abyssal and hadal megafauna in the Northwest Pacific to date.” The team also highlighted some surprises in the data, including an event they described as “the most enigmatic encounter” of the expedition.
During one of these expeditions, the team filmed what they described as a “unique, slow gliding organism” that they had not previously seen. Before the shock wore off, the team saw it again. Notably, both encounters occurred at depths reaching 9,137 meters below the surface.
Since the encounter, the team has consulted several taxonomy experts to identify the mystery organism. Although they had initially classified it with the temporary designation of Animalia incerta sedis, the team noted that “the animal cannot be confidently assigned to any known phylum.”
“While it shares some visual traits with nudibranchs or sea cucumbers, its identification remains a mystery,” they explained.
Additional Discoveries Include a Massive “Supergiant” Scavenging Amphipod
Aside from the still unidentified mystery organisms that twice glided past the camera’s lens, the expeditions also recorded several other significant discoveries. These included unprecedented, up-close observations of “rare behaviors” of animals in their natural benthic habitats.
During one crewed outing, the scientists traversed what they described as crinoid ‘meadows’ consisting of over 1,500 stalked crinoids. Each stalk was anchored to deep-sea rock terraces, enhancing the scene’s visual impact.
During another session, a camera on one of the baited traps in the Izu-Ogasawara Trench captured carnivorous sponges of the family Cladorhizidae thriving at depths of 9,568 to 9,744 meters. According to the team’s statement, the encounter with carnivorous sponges at such extreme depths represents the “deepest in-situ observation” of its type to date.
Another exciting piece of footage depicted a snailfish feeding from one of the baited landers at 8,366 meters below the surface. The team said this recorded moment represented the “deepest in-situ observation of a fish ever recorded.”
Finally, the crews and landers spotted the massive “supergiant” scavenging amphipod, Alicella gigantea, in each of the three surveyed trenches, “as well as several other bait-attending fishes and invertebrates at great depth.”
Establishing a Foundation for Future Exploration
When discussing the diverse ecosystem and unexpected discoveries in the three deep-sea trenches, the research team noted differences in biological diversity among the trenches. For example, they observed the highest number of morphotaxa in the Japan Trench, revealing the differences in nutrient exchange and other processes between the various trenches
Although the team identified the effects of geological and environmental impacts on the local ecosystems, they were also unable to avoid evidence of human activity within the trenches. This included discarded human ‘debris’ that has worked its way to these depths over time.
When discussing the value of their findings to other researchers, the team said they hope that producing a comprehensive, illustrated guide of these habitats can “support future imagery-based biodiversity surveys.”
“This study was not simply about observing deep-sea organisms but also aimed to establish a foundation for future research at these depths,” the team explained. “More than anything, the hadal zone remains one of Earth’s least explored and most intriguing frontiers.”
The study “Faunal biodiversity of the lower abyssal and hadal zones of the Japan, Ryukyu and Izu-Ogasawara trenches (NW Pacific Ocean; 4534-9775 m)” was published in Biodiversity Data Journal.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.