Lifting a thin shelf of volcanic lava at a deep-sea hydrothermal vent revealed a warm, water-filled cavity occupied by adult tubeworms and other animals. The discovery, reported in a 2024 Nature Communications study, shows that animal life at this East Pacific Rise site extends beneath the visible seafloor—not just across it.
What scientists found beneath the seafloor
The team examined six cavities beneath lobate-lava shelves at the Fava Flow Suburbs vent site near 9°50′N on the East Pacific Rise, about 2,515 meters below the ocean surface. Five cavities, each about 10 centimeters high, were visibly inhabited. The animals included adult tubeworms and a range of mobile vent fauna.
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The study’s authors describe this as the first reported discovery of animals excavated from shallow subseafloor cavities at deep-sea hydrothermal vents. The surprise was not simply that life thrives in a harsh environment: it was that a community of larger animals occupied a hidden habitat beneath the seafloor.
Tubeworms, limpets and other animals
- Oasisia alvinae tubeworms had tubes up to 20 centimeters long, a record length reported for the species.
- Riftia pachyptila tubeworms reached up to 50 centimeters long.
- Some tubeworms had reproductive organs. Two males contained sperm and two females contained large eggs, evidence that reproduction may occur below the seafloor.
- Other animals included Paralvinella, limpets, Neomphalus, Nereis, Archinome and additional polychaetes and gastropods.
How researchers reached the cavities
The work was conducted by the remotely operated vehicle (ROV) SuBastian. Rather than sending the vehicle through the ocean floor, the team worked at the exposed edges of thin lava shelves: they drilled and widened small holes, sampled vent fluid, suction-collected organisms and lifted whole shelves to reveal the cavities underneath. The Associated Press described the operation as an underwater robot overturning volcanic slabs.
That access matters because the cavities are hidden below the visible surface, not open chambers a diver could simply enter. The team’s observations came from a limited number of openings and lifted shelves at one site.
What conditions were measured inside the inhabited cavities?
Bright and colleagues reported these measurements for the five inhabited cavities in their 2024 Nature Communications study:
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| Measurement | Reported result |
|---|---|
| Maximum temperature | 18.1 ± 7.1 °C |
| pH | 6.1 ± 0.4 |
| Salinity | 33.8 ± 0.4 |
The study also measured sulfide and oxygen. These conditions describe the cavities observed at this site; they should not be treated as a universal profile for hydrothermal vents or subseafloor habitats elsewhere.
How the hidden habitat may connect to the vent above
The authors propose that cold seawater enters porous volcanic rock in a recharge zone, mixes with warmer hydrothermal fluid and then exits through cracks. Larvae could be carried by that circulation and settle in cavities or cracks before growing; mobile animals may also crawl through cracks. The study observed animals in the cavities, while the precise routes by which larvae reach them remain a proposed explanation.
This model makes the visible vent community and the cavities part of a potentially connected habitat. Many vent animals host dense bacterial symbionts that use reduced chemicals and fix carbon, so expanding the known animal habitat into the crust could change estimates of how much biological activity contributes to local and regional geochemical fluxes.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the discovery does—and does not—show
The findings establish animal life in shallow cavities at one East Pacific Rise site. They do not establish how widespread such colonies are: the study says the cavities’ three-dimensional extent has not been quantified, and it remains to be tested whether comparable communities occur beneath vents elsewhere.
The discovery also strengthens the case for protecting hydrothermal vents from potential impacts such as deep-sea mining. If vent habitats extend beneath the visible seafloor, disturbance to the area may affect more than the animals and structures that can be seen from above. The extent of that risk cannot yet be measured from this single-site observation.
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Because the ecosystem runs on chemical energy rather than sunlight, it may help scientists think about what makes life possible in other environments. But finding animals beneath Earth’s seafloor is not evidence of life on another planet.
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Study co-author Sabine Gollner told the Associated Press, “This was totally unexpected.” The authors’ central conclusion is that “the seafloor and subseafloor faunal communities are connected.”
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