ROV framegrab of Pacific white skate egg sacs near a black smoker in the Galapagos. Photo Courtesy Ocean Exploration Trust

Hydrothermal vents, where heat and minerals from the Earth’s interior bubble to the seafloor, foster unique and under-appreciated ecosystems. New observations from the Galapagos suggest that at least one species, the Pacific white skate (Bathyraja spinosissima), uses these vents to incubate its egg cases—a behavior the scientists who documented it don’t believe has ever been observed before in a marine animal.

The discovery underscores just little we understand about the deep ocean, and how important it is that we learn more before it’s too late.

“We need to dedicate more time and resources to explore in our backyard,” Pelayo Salinas de León, a marine ecologist with the Charles Darwin Foundation who led the expedition that made the discovery, told Earther. “We’re hoping to send rockets to the Moon and Mars, but we have a whole alien world next to us that hasn’t been explored.”

Photo Courtesy Ocean Exploration Trust

The Pacific white skate is one of the deepest of all known skate species, a group of flattened, cartilaginous fish that are often confused with stingrays. Known only from a few scattered specimens off the coast of Oregon, Costa Rica, and now the Galapagos, its ecology is basically a question mark.

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Now, we have our first fascinating clue. In 2015, during a remote-operated vehicle survey of Iguanas-Pinguinos, a hydrothermal vent field located 45 km (30 miles) north of the Galapagos’ Darwin Islands and roughly 1,660 meters (5,500 feet) down, researchers documented 157 egg cases, most within 150 meters (492 feet) of two active black smoker chimneys—hydrothermal vents that spew out hot sulfide minerals. Four egg sacs were collected, and DNA analysis was used to confirm their identity.

The business card-sized egg cases ranged in color from golden to dark brown, suggesting they were in different stages of incubation. Spent egg cases found in the same area suggested it had probably been used as a nursery for years. Taken together, the researchers wrote in their paper published today in Nature Scientific Reports, the evidence “implies that this species is utilizing heat at the active Iguanas-Pinguinos vent site to incubate its egg-cases.”

An egg sac captured by an ROV in the Iguanas-Pinguinos, a hydrothermal vent field. Photo Courtesy Ocean Exploration Trust

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This sort of volcanic incubation is incredibly rare. A single bird species endemic to the island of Tonga is known to bury its eggs in volcanically-heated sand, and fossil evidence suggests that certain sauropod dinosaurs of the Cretaceous Period did something similar. Salinas de LeĂłn suspects the behavior could offer a huge advantage to slow-growing skates living in the near-freezing environments of the deep ocean, helping to accelerate embryo development.

Diva Amon, a deep sea biologist at the Natural History Museum, London who wasn’t involved with the study, said her first reaction to the paper was “wow, this is wildly cool.”

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“It’s one of those neat little natural history type observations you don’t get to make very often,” Amon told Earther. “Especially with a charismatic animal in the deep ocean.”

Amon noted that while this particular volcanic nursery falls in an Ecuadorean marine sanctuary, many similar deep sea habitats have no protections. Hydrothermal vents are one of several deep ocean habitats being targeted by a nascent deep ocean mining industry, which is interested in exploiting the rare and precious metals found at them.

Last year, a group of scientists wrote a letter warning that the impacts of deep ocean mining could “last forever on human scales, given the very slow natural rates of recovery in affected ecosystems.”

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As Amon put it, the finding that at least one animal uses these vents as a nesting site “has big implications because we don’t know if this kind of behavior is happening at other vent sites and with other species. There are probably others we haven’t noticed or come across yet.”

A black smoker vent. Photo Courtesy Ocean Exploration Trust

“It just highlights how little we still know about the deep sea,” she continued. “Hydrothermal vents are one of the best studied habitats in the deep ocean, and yet still, we are making discoveries about them.”

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Hopefully, as more expeditions highlight just how full of life these alien ecosystems are, people will start pressuring their leaders to protect them.

Update: This article has been updated to reflect Diva Amon’s new affiliation at the Natural History Museum London