Hidden life thrives in ocean's secret volcanic caves

An international team of scientists, led by Monika Bright from the University of Vienna, made a surprising discovery. It concerns a hidden world of marine animals beneath the surface of the Pacific Ocean floor.

At a depth of 2,520 metres, in the hydrothermal field of the East Pacific Rise, previously unknown underground cavities were found, which serve as habitats for various organisms. The discovery suggests that hydrothermal marine ecosystems are more complex than previously assumed due to the challenging conditions there: high pressure, intense cold, and darkness.

The discovered cavities were a surprise to scientists. Geologists had previously described these cavities, but according to Monika Bright, biologists were unaware of their existence. During research conducted using the remotely-operated vehicle SuB-astian, operating from the research vessel Falkor, scientists were exploring life around underwater hot vents.

Their attention was caught by the mentioned cavities, found about 10 centimetres below the surface. Monika Bright explained this extraordinary moment in an interview with ScienceAlert: "When we tried to collect rocks to look for tube worm larvae on their surfaces, we broke into the caves and discovered animals."

Inside the hidden cavities, where the water temperature reached about 25 degrees Celsius due to the heat from volcanic activity, scientists recorded at least ten species of animals. Among them were polychaetes, sea snails, and giant tube worms like Riftia pachyptila. Interestingly, some species were also visible on the ocean floor, suggesting potential connections between the underground and above-ground environments.

Research published in the journal Nature Communications suggests that larvae can colonize the surface of hydrothermal vents from hidden cavities under the sea floor.

"The fact that large, living tube worms were found confirms the hypothesis that larvae can colonize the openings from below," added Bright. Scientists suggest that underground animal communities may play a crucial role in quickly colonizing the surface after volcanic eruptions.

So far, it is unclear how extensive these hidden cavities are, how commonly they occur, or what significance they have for the entire hydrothermal ecosystem. Their discovery presents a significant challenge for scientists to explore their extent. Researchers also emphasize the need to protect these ecosystems from human activities, such as deep-sea mining.