Scientists Catalog 100+ Animal Types Thriving In Earth’s Deepest Ocean Trenches

Fish gliding through pitch-black water more than five miles down. Sea cucumbers inching across a floor nearly six miles beneath the surface. Sponges, jellyfish, and worms thriving in a zone of bone-crushing pressure most people assume is completely lifeless. An international research team just produced the most detailed visual catalog of animals living in three of the Pacific Ocean’s deepest trenches, challenging outdated assumptions about what survives in the ocean’s most extreme depths.

During a 2022 expedition aboard the DSSV Pressure Drop, scientists used a crewed submersible called Limiting Factor and three free-falling camera platforms to log roughly 460 hours of video across the Japan, Izu-Ogasawara, and Ryukyu trenches off Japan’s coast. At depths between about 2.8 miles and more than six miles down, they documented at least 108 distinct animal types spanning worms, shrimp, fish, anemones, sea cucumbers, and single-celled organisms visible to the naked eye. Published in the Biodiversity Data Journal, the paper doubles as an illustrated field guide, the first of its kind for these extreme depths, designed to help future researchers identify what they are seeing when cameras descend to some of the least explored terrain on Earth.

Into the Deep-Sea Trenches: How the Survey Worked

Three camera platforms, named Skaff, Flere, and Closp, were rigged with high-definition cameras, bait to attract mobile animals, and instruments to measure water temperature and depth. They sank freely to the seafloor across 59 successful drops. Limiting Factor contributed seven submersible dives, including descents to the deepest points of all three trenches. Unlike the stationary platforms, it could roam across soft sediment, rocky outcrops, and steep slopes, reaching animals that would never approach bait. All three trenches sit within Japan’s exclusive economic zone in the Northwest Pacific, each formed where tectonic plates collide and one grinds beneath the other. Japan Trench reaches about five miles at its deepest; Izu-Ogasawara plunges to nearly six; Ryukyu bottoms out at roughly 4.6 miles.

108 Animal Types Cataloged in Earth’s Deepest Ocean Trenches

Every animal in the footage was identified as precisely as possible based on appearance, movement, and behavior, with many sorted into broad visual categories rather than confirmed species. Japan Trench showed the most variety at about 78 percent of all categories logged, followed by Izu-Ogasawara at roughly 58 percent. More than 40 percent of animal types turned up in just one trench.

Among the standout records: a snailfish observed at 8,336 meters in the Izu-Ogasawara Trench, reported as the deepest fish ever recorded. A grenadier fish was seen at 7,259 meters, representing the deepest known use of a gas-filled swim bladder in any fish. Crinoids, flower-like relatives of starfish, formed dense clusters on rocky terraces nearly six miles down, with researchers counting 1,524 individuals over a single four-hour transect.

A “supergiant amphipod,” a scavenging shrimp-like creature of unusual size, was documented in all three trenches for the first time. Predatory versions were caught hunting smaller relatives near the bait; submersible footage then showed the same predators sitting motionless on rocks, a behavioral detail that baited cameras alone would never have captured.

Strange Life in the Deep-Sea Trenches

Sea cucumbers ranked among the most varied groups, with at least 20 types documented, some swimming freely, others confined to the bottom. Worms proved equally diverse at 18 types, with researchers sometimes relying on swimming style to tell them apart: one rotated like a corkscrew, another flexed side to side. Seven anemone types were separated by differences in column length, tentacle count, and disc proportions, with some displaying extremely elongated columns and others having practically none.

A meat-eating sponge found between about 5.9 and 6 miles deep in the Izu-Ogasawara Trench marked the deepest confirmed observation of carnivorous sponges on record. Researchers also encountered something they could not classify at all: a slow-gliding organism recorded at 8,022 meters in the Japan Trench and again at 9,137 meters in the Izu-Ogasawara Trench that stumped multiple taxonomic experts. It has been filed as “Animalia incerta sedis,” meaning animal of uncertain placement.

Why This Deep-Sea Field Guide Changes the Picture

Before this expedition, the last full-ocean-depth submersible to visit these trenches was a French vessel in the 1960s. Japan’s deep-diving vehicle Kaiko was lost in 2003. For decades, direct visual records from these depths were scarce, and historical exploration relied on nets and dredges that often destroyed the very animals they collected. Pairing baited platforms with a roving submersible gave the team a broader picture of biodiversity than either method could manage alone, and researchers published the results as a freely accessible reference for future expeditions.

Deep ocean below about 1.9 miles covers roughly half of all ocean floor on Earth, yet scientific knowledge of life there trails far behind what is known about shallower water. With deep-sea mining advancing and climate change reshaping ocean chemistry at every depth, knowing what actually lives in these places matters more than ever. A catalog of 108 animal types from trenches nearly six miles deep makes one thing clear: the abyss is anything but empty.

---