Life in the Hadal Zone: Creatures Below 6,000 Meters

The hadal zone — named after Hades, the Greek underworld — encompasses the deepest trenches of the ocean, plunging below 6,000 meters. These extreme environments were once thought to be barren wastelands, devoid of life. Modern expeditions have shattered that assumption entirely.

In a landmark 2022 expedition to four hadal trenches around Japan, researchers from the University of Western Australia and Tokyo University of Marine Science and Technology documented a Pseudoliparis snailfish at a record depth of 8,336 meters in the Izu-Ogasawara Trench — the deepest fish ever filmed. The record was officially certified by Guinness World Records in April 2023. The finding was published in Deep-Sea Research Part I (Jamieson et al., 2023, DOI: 10.1016/j.dsr.2023.104132).

The expedition, conducted aboard the deep-sea survey vessel DSSV Pressure Drop as part of the "Ring of Fire 2022 Japan Expedition," deployed traps and video landers between 4,534 and 9,773 meters. Snailfish were observed between 6,824 and 8,336 meters, with two specimens of Pseudoliparis belyaevi physically collected from 8,022 meters — the deepest fish ever caught.

These creatures survive at pressures exceeding 800 atmospheres through remarkable biochemical adaptations. Their cell membranes are packed with unsaturated fatty acids that remain fluid under crushing pressure, and they produce high concentrations of trimethylamine oxide (TMAO), a molecule that stabilizes proteins against pressure deformation. Their skeletons are soft and flexible, and they are covered in a gelatinous layer rather than scales — an energetically efficient adaptation in a food-scarce environment.

Professor Alan Jamieson, chief scientist of the expedition, noted: "We have spent over 15 years researching these deep snailfish; there is so much more to them than simply the depth, but the maximum depth they can survive is truly astonishing."

The hadal zone also plays a critical role in the global carbon cycle. Organic matter — dead plankton, fecal pellets, and marine snow — rains down from the surface and accumulates in trenches. Microbial communities break this material down, sequestering carbon for millennia. Understanding these processes is vital for climate modeling.

Future expeditions aim to map the full extent of hadal biodiversity and understand how these ecosystems might respond to deep-sea mining operations, which threaten to disturb sediment layers that have remained undisturbed for millions of years.