Under a Hellish Ocean Habitat, Bizarre Animals Are Lurking

Off the western shores of Central and South America, there is a Lovecraftian, lava-licked realm thousands of feet beneath the ocean. There, on the seafloor, volcanically powered exhaust ports known as hydrothermal vents fire off jets of water that reach temperatures of up to 700 degrees Fahrenheit. While the surfaces and peripheries of these vents have long been known to host a diverse mosaic of life, scientists had never known animals to find a home beneath these hellish geysers.

But that changed in July when a diving robot overturned volcanic bedrock pockmarked with hydrothermal vents and revealed an explosion of animal life — including an abundance of tubeworms, bizarre creatures that resemble sentient spaghetti.

“This is the first time that animal life was found below the surface” of hydrothermal vents, said Monika Bright, an ecologist at the University of Vienna and lead scientist on the expedition.

Microbial life was previously known to exist within these hollows. But the idea that animals were ensconced within vaults of volcanic rock, bathing in darkness, seems shocking. “The deeper you go, the warmer it goes, the less oxygen there is, the more toxic chemicals are in it,” Dr. Bright said. “It’s very shallow, but it’s still below the Earth’s crust.”

But not all experts were so surprised by the discovery.

“I think it makes perfect sense,” said Julie Huber, a marine geochemist and microbiologist at the Woods Hole Oceanographic Institution in Massachusetts who wasn’t involved with the work. “The shallow subseafloor, where temperatures are likely cool enough for animals to survive, is what I think of as a ‘subseafloor conveyor belt’ for microbes, nutrients and, now, animals.”

Much about these unusual habitats is a mystery. But, like many revelations found at the bottom of the sea, this discovery once again pushes the boundaries of what scientists consider possible — perhaps even normal — for life on Earth.

Hydrothermal vents, first discovered off the Galápagos Islands, are Dalí-esque chimneys and chasms that often grow atop or close to midoceanic ridges — vast volcanic fissures in the seafloor made by the divergence of two tectonic plates. Deep below, the magmatic heat roasts percolating seawater, which jets back out into the water column as superheated, mineral-rich soups.

Despite their extreme natures, these vents are metropolises of strange critters. Common among them are tubeworms, which start life as free-swimming larvae before becoming immobile adults that grow to several feet in length and that are fed by sulfur-eating bacteria living in their guts.

Dr. Bright suspected that these wiggly weirdos could also be found beneath the vents. “It’s kind of a really crazy idea I had,” she said.

To find out — and to improve our understanding of the connections between life above and below hydrothermal vents — Dr. Bright led a team aboard Falkor (too), a research ship owned by the Schmidt Ocean Institute. From June 27 to July 29, the researchers sailed to an eruption-prone section of the East Pacific Rise, a spreading seafloor schism that runs roughly parallel to South America.

There, they set loose SuBastian, a remotely operated vehicle with two armlike appendages to which drills, scoops and saws can be affixed. It approached the frothing vents, politely flipped some volcanic rocks and peeked inside.

It exposed what geologists sometimes refer to as hollows — labyrinths of glassy rock cavities stretching in several directions, some decorated with arches and pillars made of once-molten lava now frozen in time. Through these tunnels, water was flowing at a surprisingly temperate 75 degrees Fahrenheit. And every time the submersible looked inside these concealed geologic mazes, it saw animals, including myriad adult tubeworms.

“They were just growing in there, living in there,” Dr. Bright said. Snails, as well as different types of slithering worms, were also slinking about.

The discovery raises new questions about deep-sea ecosystems. For instance, are there links between the types of animal life and microbes found within the hollows? “I also can’t help but wonder if there is some life stage more commonly found in the subseafloor, such as larvae,” Dr. Huber said.

For some, this discovery has engendered dreams of otherworldly life. “I always think about ocean worlds when I am studying vents,” Dr. Huber said. Biological crucibles may exist within the icy, carapace-covered seas of Enceladus, a moon of Saturn that has key ingredients for life and that potentially may also have hydrothermal vents on its seafloor.

But for Dr. Bright, Earth is all that matters. “I’m not thinking of other planets and moons — I’m thinking that there’s so much mystery to be discovered in our Earth,” she said. “I feel like I know this place. I’ve studied this place for 30 years. And still, you can find something unexpected.”