When scientists set out in subsea vehicles to explore the Dorado Outcrop, their intention was to study a cooled-down hydrothermal system. Instead, as they reported in the March edition of Deep Sea Research Part I, when they were a hundred miles off the coast of Costa Rica they encountered something that had never been seen before: a huge crew of octopus moms of a completely unknown species.

In the paper, the cross-disciplinary team of researchers describe their confusion. While they eventually determined that the octopuses belong to the deep sea genus Mussoctopus, that is one of the few things they know for certain. They’re confused that the creatures, known for being loners, were suddenly congregating in clusters of 100, nearly all of them females guarding eggs. It’s especially perplexing that they would set up a nursery in such a hostile place: the region’s rocky seafloor consists of hardened lava that once spewed from an underwater volcano, and warm fluid still spurts from the cracks. According to a statement released Monday by the study authors, settling down there is essentially suicide. When co-author and Field Museum curator Janet Voight, Ph.D. saw them, she immediately thought: “No, they shouldn’t be there!”

Octopuses
A group of brooding octopuses on the ocean floor.

It was a confusing sight indeed. Deep-sea octopuses live in cold temperatures, and this region, smack in the Caribbean, is far too hot. The octopus mothers, furthermore, showed severe stress, and none of the 186 eggs they observed had any signs of a developing embryo. The authors described these particular octopuses as “doomed,” but fortunately their huge numbers suggest a healthier habitat nearby. The authors also observed octopus arms peeking out from the crevices inside the rocks, where the water is probably colder and richer in oxygen. Because a female octopus only has one clutch of eggs during its entire life cycle, the existence of another, safer population is integral.

“In order for this huge population to be sustained, there must be even more octopuses to replace the dying mothers and eggs that we can see,” Voight explained. “Odds are it has hollow areas where other females nurture their eggs to hatching. They are analogous to the boomers who have all the good jobs, while the millennials wait, seeking just one little piece of the cool rock.”

Those crevices must be one dope spot to raise an octopus baby, because the overflow of the octopus moms into the dangerously warm region means almost certain death for those displaced broods. While some oceanic animals like Pacific white skates purposefully lay their eggs around hydrothermal vents, the octopuses’ clutch formations in those areas appear to be repercussions of limited real estate.

“Never would I have anticipated such a dense cluster of these animals at 3,000 meters depth, and we argue that the numbers of octopuses we see are simply the surplus population,” says Voight. “What else is down there that we can’t even imagine? I want to find out.”