Seventeen octopods huddled on the Dorado Outcrop, most in a brooding posture.
Photo: Phil Torres, Dr. Geoff Wheat

Scientists have made a truly bizarre discovery on an expanse of cooled lava 150 miles west of Costa Rica and nearly two miles underwater. There, they laid eyes on more than a hundred female octopuses, tending to eggs that didn’t seem to be growing in water that seemed too warm for their liking.

Deep sea octopuses are a rare sight, and it’s even rarer to catch them in the act of brooding. So when Janet Voight, a deep sea biologist at the Field Museum of Natural History, examined footage collected at the Dorado Outcrop during a 2013-14 study of warm hydrothermal fluids seeping out of cracks in the rocks, it was nothing short of shocking to discover an enormous camp of tentacled, seemingly-expectant moms.

Closer examination of the footage revealed the big-eyed purple saucers to be members of the genus Muusoctopus, possibly representing several new species of deep sea octopus. To Voight and the other scientists behind this remarkable discovery, it suggests an even larger population of octomoms may be lurking unseen in cracks and tunnels on the ocean floor.

“It’s like, amazing,” Voight told Earther.

It’s also puzzling, because deep sea octopuses tend to thrive in near freezing temperatures. Warm water speeds up their metabolism, causing them to use up too much oxygen. And indeed, when lead study author Anne Hartwell examined the octopods’ breathing patterns in hundreds of hours of video footage collected by an ROV and a crewed underwater vehicle, she learned that those in or near hydrothermal fluids were breathing faster, suggesting oxygen stress.

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Moreover, none of the nearly 200 eggs the researchers examined appeared to be developing at all.

“We argue that the elevated temperatures and low oxygen concentrations in discharging fluids generate severe and potentially lethal physiological stress for these octopods and their eggs,” the authors write in the paper published in Deep Sea Research Part I.

The researchers go on to speculate that females are drawn to the area because of the lack of sediment, which makes it easier to anchor their eggs, blissfully unaware of their new home’s thermostat problem. As the authors explain, hydrothermal fluid discharges can ramp up quickly at any given site, and once a female chooses a place to brood, she’s stuck with it—stressful environment or not.

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It’s a speculative idea that could provide unique insights, but requires deeper investigation to be verified.

After all, many animals seek out warm waters to speed up the incubation process, including some deep sea skates that lay their eggs near hydrothermal vents, as detailed in a recent paper in Nature Scientific Reports.

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“Both papers [the skate and the octopus paper] are quite speculative as we cannot say for certain what the effect of the raised temperatures is and of course they may affect different species in different ways,” Diva Amon, a deep sea biologist at the Natural History Museum, London who wasn’t involved with either study, told Earther in an email.

Nicole Morgan, a deep sea biologist at Florida State University who also wasn’t involved, told Earther in a Twitter DM that while the water is warm, it’s “not outside known ranges for the octopus genus.” The oxygen levels are also low but not lethal, she said, suggesting “the authors are probably right that this is sub-par brooding habitat.”

“I think they have captured a snapshot of what evolution looks like in real life—they are brooding in an area that is stressful but available and not immediately lethal,” Morgan continued. “More likely than not this subpopulation will die out because of the high egg fatality, but if some eggs do survive, that could be a start to speciation.”

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Amon added that the discovery was “super cool,” and that it shows “how much more we have to learn about the deep sea as we cannot definitively say what is happening here.”

The study’s authors, for their part, suspect there’s far more to the discovery than meets the eye. They think the stressed-out brooding colony they observed indicates much larger population of healthy individuals tending eggs nearby. Perhaps these more privileged moms lurk inside the Dorado Outcrop, in lava-extruded tunnels where the water is cooler and more breathable.

Such a population would be hard to detect, even for ROVs. But it boggles the mind to imagine the existence of a secret group of octomoms raising their young in the dark, here or elsewhere on the millions of seamounts and outcrops littering the ocean floor.

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“What does this mean for what else is out there that we have no clue [about]?” Voight said.