10,000 m below the sea, life teems with worms and molluscs

Jules Verne dreamed of it! A Chinese submersible has discovered mollusks and worms living nearly 10,000 meters beneath the sea, the deepest colonies of organisms ever observed.

This discovery suggests that other organisms could thrive in the extreme conditions of the largely unexplored ocean floor on our planet, the team of Chinese scientists said in a paper published Wednesday in Nature .

Most life on Earth depends on sunlight, which is essential for photosynthesis. But in the pitch-black darkness of the ocean floor, some living things survive thanks to chemicals, such as methane, that escape from cracks in the ocean floor. Scientists call this process chemosynthesis.

Last year, the Chinese submersible Fendouzhe (The Battant) dived 23 times in the Mariana Trench in the western Pacific Ocean with researchers on board, according to the study in Nature .

They discovered colonies of thousands of tubeworms (whose bodies are inside a tube) and molluscs called bivalves, at depths ranging from 2,500 to 9,533 m.

A video released with the study shows entire fields covered in worms, up to 30 cm long, as well as clusters of mollusks and clams.

Spiny crustaceans, floating marine worms, sea cucumbers, sea lilies (crinoids) and other animals have also been observed.

These are "the deepest and largest chemosynthesis-based communities known to date on Earth," the study said.

Given that other ocean trenches exhibit similar characteristics, such communities "may be more widespread than previously thought," the authors say.

They say they also found "convincing evidence" of methane production by microbes, with tubeworms tending to cluster around snow-like microbial mats.

Gigantic pressure

The study's publication comes as the controversial issue of deep-sea mining is under international debate. Both China and the United States have expressed interest in extracting coveted minerals from the depths.

Oceanographers warn that mining a largely unexplored ocean floor—one of the planet's last remaining wildernesses—could decimate fragile and little-understood ecosystems.

Despite recent talks, the International Seabed Authority (ISA), which oversees mining in international waters, has still not adopted rules to regulate the industry.

Chinese media have already reported that the Fendouzhe submersible's mission also aims to conduct research on "deep-sea materials."

Only a handful of people have been able to visit the bottom of the Mariana Trench, the deepest underwater valley on our planet.

The first explorers reached the pit – a crescent-shaped depression deeper than the height of Everest – in 1960.

No other mission was conducted there until the first solo journey to the bottom by American filmmaker James Cameron in 2012. The director of The Abyss described the landscape as "alien" and "desolate."

The pressure at the bottom of the pit reaches more than one ton per square centimeter, nearly 1100 times that at sea level.