In a First, Scientists Find Animals Thriving Beneath the Ocean Floor in Hidden Habitats Near Deep-Sea Vents

In summer 2023, researchers deployed a remotely-operated underwater vehicle called SuBastian to investigate hydrothermal vents on the southeastern Pacific Ocean floor. But when SuBastian flipped over a small section of ocean crust, the team discovered something unexpected beneath it: Worms, snails and other marine invertebrates were living in cavities under the seafloor.

“To our knowledge, it is the first time that animal life has been discovered in the ocean crust,” Sabine Gollner, a marine biologist at the Royal Netherlands Institute for Sea Research, tells Reuters’ Will Dunham. Gollner is a co-lead author of a study detailing these findings, which was published in the journal Nature Communications last week.

Hydrothermal vents are cracks in the ocean floor that release hot, mineral-rich water into the deep sea. They form when seawater seeps into Earth’s crust in areas where tectonic plates are either spreading or subducting—creating sites where magma is closer to the surface. The seawater gets heated by the magma, which sends it shooting back up into the deep ocean, along with a wealth of life-sustaining minerals that support a whole ecosystem of organisms in proximity to the vents.

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Back in 2023, the researchers unleashed SuBastian from a Schmidt Ocean Institute research vessel to understand how tubeworms—narrow-bodied creatures that form iconic, towering colonies—spread from vent to vent. As adults, the worms anchor themselves to the seafloor. But scientists wondered if, during their unanchored larval stage, young tubeworms might spread through cavities beneath the seabed formed by the vapor created when lava comes into contact with seawater.

“We thought that tubeworm larvae might disperse through these spaces, being drawn in with cold water entering the Earth’s crust through cracks in the rocks. This water mixes underground with hot vent fluids and then is expelled elsewhere, taking the larvae along with it,” Gollner explains to the London Natural History Museum’s James Ashworth.

The team directed SuBastian to dig up parts of the seafloor 1.56 miles beneath the surface of the ocean near the Fava Flow Vents on the East Pacific Rise. That was when they found life: The sub-seafloor cavities of water mixed with magma were filled with giant tubeworms—both larvae and adults—carnivorous bristle worms, sediment-eating snails and more.

“Animals are able to live beneath hydrothermal vents, and that, to me, is mind-blowing,” Gollner says in a Schmidt Ocean Institute video, per CNN’s Ashley Strickland.

While scientists had previously identified animals living above the seafloor near hydrothermal vents, this was the first time animals had been found living underground near the vents—only microbes had been seen there before, per National Geographic’s Olivia Ferrari.

SuBastian’s exploring revealed those unexpected findings, but it also shed light on the team’s central question about tubeworms.

“The fact that live large tubeworms were found means that the hypothesis of larvae being able to colonize vents from below has been confirmed,” marine biologist Monika Bright of the University of Vienna, a co-lead author of the study, tells ScienceAlert’s Michelle Starr. “Some settle if conditions are right in the subsurface, some might with the vent flow be flushed out from the subsurface and colonize the surface.”

The cavities were about four inches beneath the seafloor and filled with 77 degree Fahrenheit water. But scientists still aren’t sure how far these cavities extend, both horizontally and vertically. Microbes might be able to live more than six miles below the seabed, but animals likely have a smaller range.

Regardless, the discovery means these hydrothermal vent communities—unique hotspots of extreme underwater life—extend beyond what is visible.

“Every study just confirms how little we understand about the seafloor,” Rachel Lauer, a geologist at the University of Calgary in Canada who was not involved in the new research, tells National Geographic.

What the scientists are more certain about, however, is the need for further protection of hydrothermal vent environments from human activities such as deep-sea mining, as they continue to study this unique phenomenon. Researchers say these still-mysterious, extreme habitats might hold implications for how life survives without sunlight elsewhere—perhaps even on other planets.

Margherita Bassi | READ MORE

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.