CALIFORNIA  -  Scientists have uncovered communities of animals such as tube worms and snails living in volcanic caves beneath the seafloor, revealing a previously unknown but thriving ecosystem. Researchers made the astonishing discovery during a 30-day expedition aboard the Schmidt Ocean Institute’s research vessel “Falkor (too)” to explore an undersea volcano off Central America that’s part of the East Pacific Rise. A volcanically active ridge, the extensive rise occurs where two tectonic plates meet on the floor of the Pacific Ocean. Located along the ridge are hydrothermal vents, or openings in the seafloor where seawater and hot magma from beneath Earth’s crust come together to create a type of underwater hot spring. A variety of sea life clusters around the vents, which belch out elements that help bacteria, mussels, tube worms and other animals survive at extreme ocean depths. The vent ecosystem has been studied in-depth, but areas beneath the vents have largely remained out of reach. Using the remotely operated vehicle SuBastian, researchers exposed parts of the subseafloor and uncovered a surprise: caves connected to the vents teeming with giant tube worms, some reaching up to 1.6 feet (0.5 meter) long, and other animals. The revelation suggests connectivity between the seafloor and subseafloor ecosystems, allowing life to thrive in unexpected places above and below the ocean floor.

While the team first observed the subseafloor ecosystem in the summer of 2023, the research describing the environment and its animals published Tuesday in the journal Nature Communications.  “We want to understand how animals travel and how they disperse, so we looked for the first time into the subsurface,” said study coauthor Dr. Sabine Gollner, marine biologist and senior scientist at the Royal Netherlands Institute for Sea Research, in a video the Schmidt Ocean Institute released. “Animals are able to live beneath hydrothermal vents, and that, to me, is mind-blowing.” Scientists have long been intrigued by the animal life that clusters around hydrothermal vents and have studied these unique ecosystems for the past 50 years. The shifting of Earth’s tectonic plates gives rise to new hydrothermal vents over time, and foundational seafloor animals such as tube worms have been known to colonize these new vents in the span of a few years. Microbial life exists beneath the seafloor based on samples from fluid released by the hydrothermal vents, some research has also suggested. And tube worms were observed living several centimeters deep within the cracks of the seafloor near vents, but the study team wasn’t sure how tiny tube worm larvae, less than 0.04 inch (1 millimeter) in length, would be able to swim against the current to settle and grow in these spaces, Gollner said. Tube worms are immobile creatures that settle and grow in one place without moving, like barnacles.  “That is why we hypothesized that tubeworm larvae can travel in cracks below the ground with the warm vent fluid to colonize the surface vents from below,” Gollner said in an email.