Thriving Animal Communities Found under 6 Miles of Ocean

Deep-Sea Trench Expeditions Reveal Rich Ecosystems, Reshaping Views of Life’s Limits

Tubeworms are dominant at 6,870 meters (22,500 feet) at the Aleutian Trench, with spots of white microbial mats interspersed. Credit: Institute of Deep-sea Science and Engineering, CAS (IDSSE, CAS)

A series of recent deep-ocean expeditions have uncovered astonishing animal communities thriving at extreme depths—in places long thought too hostile for complex life. These findings, drawn from multiple trench systems in the Pacific Ocean, are expanding scientists’ understanding of how life adapts to crushing pressure, perpetual darkness, and scarce food resources.

The most dramatic discoveries come from the Mariana Trench and nearby hadal trenches—the deepest parts of the world’s oceans. Using the Chinese submersible Fendouzhe, researchers made repeated dives, observing colonies of tubeworms, bivalves (clams and other mollusks), crustaceans, sea cucumbers, and other invertebrates thriving at depths approaching 9.5 kilometers (nearly 6 miles) below sea level. These are the deepest known animal communities documented to date.

Unlike most ecosystems that rely on sunlight and photosynthesis, these deep-sea communities derive their energy through chemosynthesis—a process by which microbes convert chemicals like hydrogen sulfide and methane seeping from the ocean floor into usable energy. Larger animals either feed on these microbes or maintain symbiotic relationships with them.

Life’s Adaptability

Video and imagery released alongside the research show dense fields of tubeworms, some nearly a foot long, interspersed with beds of bivalves and clusters of other invertebrates. Scientists also observed free-floating marine worms, sea lilies, and spiky crustaceans—an unexpectedly complex community for such extreme conditions.

These ecosystems were found not only in the Mariana Trench but span at least 1,500 miles across hadal trenches that include the Kuril-Kamchatka and Aleutian systems, hinting that chemosynthesis-based communities may be far more widespread than previously thought.

The discoveries are forcing researchers to rethink ocean biology and the so-called “limits” of life. In addition to macrofauna, deeper biological investigations—like the MEER project’s metagenomic surveys—reveal astonishing microbial diversity at similar depths, with thousands of previously undocumented species exhibiting unique evolutionary adaptations to pressure and nutrient scarcity.

These findings are timely as governments and industry explore deep-sea mining for minerals—a practice that scientists warn could irreparably damage fragile ecosystems that science is only beginning to understand.

Studying these deep communities not only enriches knowledge of Earth’s biodiversity but also informs broader questions about life’s resilience—including the possibility of similar ecosystems on icy ocean worlds beyond Earth.

Life Adapted to Extremes

Researchers say the animals inhabiting these hadal-zone ecosystems survive through a suite of remarkable physiological and biochemical adaptations. At pressures exceeding 1,000 times that at sea level, many organisms possess pressure-tolerant proteins and cell membranes that remain flexible rather than collapsing under compression. Genetic analyses show altered enzyme structures that continue functioning despite intense pressure and near-freezing temperatures. Some species exhibit slow metabolic rates, conserving energy in an environment where food is scarce and unpredictable.

Microbial studies suggest that many deep-sea organisms also carry genes associated with DNA repair, helping them withstand constant cellular stress.