What lives in the Mariana Trench, the deepest place on Earth

What the Mariana Trench is

The Mariana Trench is the deepest place on Earth: a crescent-shaped scar in the crust beneath the western Pacific Ocean, east of the Philippines, more than 2,550 kilometers (1,500 miles) long and 69 kilometers (43 miles) wide on average. What lives in the Mariana Trench is far less monstrous than its reputation. Scientists have documented snailfish, small crustaceans, sea cucumbers and jellyfish there, and near the very bottom, giant single-celled organisms called xenophyophores.

Where it is and how deep it goes

Where is the Mariana Trench? It curves past the Northern Mariana Islands and Guam, and its seafloor in US waters there is protected by the Mariana Trench Marine National Monument, established by presidential proclamation in January 2009. The whole monument covers about 246,608 square kilometers (95,216 square miles) and is managed by NOAA, the US Fish and Wildlife Service and the government of the Northern Mariana Islands.

The trench formed by subduction, where one oceanic plate plunges into the mantle while the other rides over it. Its deepest point, the Challenger Deep, lies roughly 11,000 meters (36,000 feet) down; a 2010 University of New Hampshire sonar survey measured 10,994 meters, plus or minus 40. Cut Mount Everest off at sea level and set it on the bottom, NOAA notes, and more than a mile of water would still cover its summit. In 2012 the filmmaker James Cameron dove to the bottom alone in the submersible Deepsea Challenger.

Beyond the trench floor, the monument protects some unusual chemistry. Its Volcanic Unit includes undersea mud volcanoes and thermal vents. The Champagne vent at the NW Eifuku volcano releases almost pure liquid carbon dioxide, and the Daikoku submarine volcano holds a pool of liquid sulfur that NOAA describes as one of a kind.

The popular claim

A popular claim about the trench is that something enormous hides at the bottom. Steve Alten's Meg novels and their film adaptation, The Meg, imagine megalodon, the giant prehistoric shark, surviving there. According to a University of Bristol paleontology explainer, the idea traces back to megalodon teeth found near the area by HMS Challenger in 1873, which looked unusually white and were dated to between 11,000 and 24,000 years old. A 1998 study showed that a thick crust of manganese dioxide had preserved them.

That is speculation, not observation. No shark has ever been recorded living in the trench, the Bristol explainer notes, and the deep sea does not hold enough food to feed even one giant predatory shark. Nothing resembling a giant appears in the camera and trap records described below; the top predator documented in the trench is a small, translucent fish.

What actually lives there

That fish is the Mariana snailfish, Pseudoliparis swirei, described in the journal Zootaxa in 2017 from 37 specimens caught between about 6,900 and 8,000 meters on 2014 and 2017 expeditions aboard the Schmidt Ocean Institute's research vessel Falkor. It is small, translucent and scaleless, and sucks in tiny crustaceans and shrimp. According to the University of Hawaiʻi, whose scientists took part, the trench's funnel shape gathers food and invertebrate prey is plentiful. The name honors Herbert Swire, an officer on the HMS Challenger expedition that discovered the trench.

Below the fish, life continues. In July 2011, Scripps Institution of Oceanography researchers and National Geographic engineers dropped free-falling camera landers into the trench and filmed xenophyophores at up to 10,641 meters in the Sirena Deep, far beyond the previous xenophyophore record of about 7,500 meters. These single-celled organisms are among the largest individual cells known, often more than 10 centimeters across, and can concentrate lead, uranium and mercury. The same footage showed the deepest jellyfish observed up to then.

The deepest fish on record

Deepest-fish records need a place and a year attached, because they keep moving. In 2017 the University of Hawaiʻi reported that a Japanese team had filmed the Mariana snailfish at 8,178 meters, which it called the deepest sighting so far. The record has since moved to another trench. In August 2022 an expedition by the University of Western Australia and the Tokyo University of Marine Science and Technology filmed an unidentified Pseudoliparis snailfish at 8,336 meters in the Izu-Ogasawara Trench, south of Japan; the find was announced in April 2023.

The same voyage caught two snailfish of the species Pseudoliparis belyaevi at 8,022 meters in the Japan Trench. The university noted that, unusually among deep-sea fish, snailfish juveniles live at the deeper end of their depth range, and the deepest individual found was an extremely small juvenile. No fish has been recorded anywhere near the full depth of the Challenger Deep.

The mystery sound, solved

One real Mariana Trench mystery has been solved. In 2014 and 2015, an acoustic glider surveying over the trench off Guam recorded a strange call: five parts over about 3.5 seconds, starting at 30 hertz and ending in a metallic sound that reached 8,000 hertz. It became known as the Biotwang. A 2016 study attributed it to a baleen whale but could not say which species.

In September 2024, a team led by Ann Allen of NOAA's Pacific Islands Fisheries Science Center published the answer in Frontiers in Marine Science. On a 2018 survey in the Mariana Archipelago, 13 large-whale sightings coincided with deployed sonobuoys; 10 were confirmed Bryde's whales, and nine of those had Biotwangs recorded. The source is a whale in the waters above the trench, not something on its floor.

What is still debated

The open questions are about limits and gaps, not monsters. The fish filmed at 8,336 meters had not been identified to species when the record was announced. The 2010 depth measurement for the Challenger Deep carries an uncertainty of 40 meters either way. Alan Jamieson of the University of Western Australia said that more than 15 years of research on deep snailfish had still left much to learn about them. What has no support is the megalodon-style giant: no shark has been recorded there, and there is no food supply that could sustain one.

Questions people ask

Verdict

The Mariana Trench explained in brief: a subduction trench in the western Pacific whose deepest point lies about 11,000 meters down, home to small, specialized life rather than giants. Real or Legend has filed this as confirmed. The Mariana snailfish at 8,178 meters, xenophyophores at 10,641 meters and Bryde's whales as the source of the Biotwang all rest on published observations. Megalodon in the trench does not; it rests on fiction and misdated teeth, and no shark has ever been recorded there.