QCOSTARICA (Mongabay.com) In 2013, scientists found octopuses doing something unusual at Dorado Outcrop, a small seamount off the west coast of Costa Rica. While most octopuses are known to be solitary animals, females had gathered at this spot to brood their eggs near a low-temperature hydrothermal vent. But at the time, scientists didn’t see any octopus babies, which led them to theorize that the warm water and limited oxygen at the vent wasn’t allowing the eggs to develop fully.

A deep-sea octopus nursery on at a hydrothermal venting site off the coast of Costa Rica. Image by Schmidt Ocean Institute.Ten years later, in June 2023, researchers plunged a remotely operated vehicle, or ROV, back into the deep sea to search for the brooding octopuses at Dorado Outcrop. They got an even bigger surprise when they found them: this time, there were babies, making the outcrop a so-called “octopus nursery.”

“​​The ROV mission control room erupted in squeals of amazement,” Beth Orcutt, an oceanographer of the U.S.-based Bigelow Laboratory, who co-led the mission, told Mongabay in an email. “People [were] pointing their fingers at the screens excitedly, clapping, hugging.”

Several days later, the researchers discovered a second octopus nursery about thirty nautical miles away from the Dorado Outcrop on another low-temperature vent. Together, these two locations are two of only three known deep-sea octopus nurseries in the world. The third is on the Davidson Seamount off the coast of California.

The biggest finding of the expedition is the confirmation that the small Dorado Outcrop in Costa Rica’s Pacific waters hosts an octopus nursery with hundreds of Muusoctopus species brooding viable eggs in low-temperature (12oC) hydrothermal fluids. This refutes a previous hypothesis that eggs are not viable in this area. Image by Schmidt Ocean Institute.Scientists believe the brooding octopus found at the warm water flow of the hydrothermal vent during this year’s expedition might be a new and yet-to-be-identified species of deep-sea octopus in the Muusoctopus genus.

Throughout the 19-day expedition, aptly called the Octopus Odyssey, they also saw at least four other species of octopus, of which three may also be unidentified species, said Janet Voight, a cephalopod mollusk expert at the Field Museum in Chicago.

Voight told Mongabay there are several competing hypotheses exist about why these octopuses are banding together to brood at the hydrothermal vent.

“It could be [that] the rocks are a great attractant, or the warm,” Voight said in an email. “Most ectothermic animals (those who don’t maintain their body temperature) prefer being warm to cool, or it could be that there is something in the water, some microbe, that helps them or their progeny survive.”

Scientists know very little about the brooding behavior of deep-sea octopuses. They do know that one deep-sea octopus from the genus Graneledone broods for about 53 months, Voight said. While the newly discovered species is in the Muusoctopus genus, she said the two species’ eggs are of a comparable size, which makes it possible that the development time is the same.

When female octopuses brood, they rest with their suckered arms around their eggs. Sometimes they squirt water over the eggs, most likely in an attempt to keep them aerated, Voight said.

“The females do not leave their eggs, nor do they eat while brooding,” she said. “The exception would be if an egg gets infected with something or somehow ‘isn’t right.’ The female will eat diseased eggs apparently to keep the rest of the clutch healthy. The females die about the time the eggs hatch, which is about when their brothers die. It is a life history that seems odd to us, but it works for them!”

Dorado Outcrop is currently unprotected from human activities, so part of the mission is to understand if this seamount and others in the area are worthy of protection, according to the expedition team.

“This expedition to the Pacific deep waters of Costa Rica has been a superb opportunity for us to get to know our own country,” Jorge Cortes, a researcher at the University of Costa Rica, who co-led the expedition with Orcutt, said in a statement. “The expedition had a significant number of local scientists and students which will accelerate our capacity to study deep regions. The information, samples, and images are important to Costa Rica to show its richness and will be used for scientific studies, and outreach to raise awareness of what we have and why we should protect it.”

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Top photo: A deep-sea octopus nursery on at a hydrothermal venting site off the coast of Costa Rica. Image by Schmidt Ocean Institute.

The biggest finding of the expedition is the confirmation that the small Dorado Outcrop in Costa Rica’s Pacific waters hosts an octopus nursery with hundreds of Muusoctopus species brooding viable eggs in low-temperature (12oC) hydrothermal fluids. This refutes a previous hypothesis that eggs are not viable in this area. Image by Schmidt Ocean Institute.