In 2018, Amanda Kahn, an invertebrate biologist at San Jose State University, joined an ocean expedition to monitor the base of Davidson Seamount, an inactive underwater volcano off the coast of central California. He came for sponges and corals.
But he and his colleagues found something even more amazing. As their remotely operated vehicle, scanning the seafloor and streaming video back to their ship, rose from behind a rock, the crew let out a sigh of relief. In the glistening water, they saw many upside-down octopuses circling rocky crevices with their arms clinging to their frames. A closer look revealed that they protect the eggs, similar to the way birds circle a nest.
“Sometimes you recognize right away the size of a special object you’ve found,” said Dr. Kahn. “And I think that was one of those really special moments.”
When James Barry, a marine ecologist at the Monterey Bay Aquarium Research Institute, saw the next expedition, he immediately wondered why there were so many octopuses. “And so we started to find out,” he said.
Dr. gathered. Barry by a team of ecologists, biologists, geologists and engineers who, over the next three years, studied what they called the “Octopus Garden” — the largest known aggregation of these creatures with eight foot It turns out that the water’s sheen is a sign: The nursery sits atop a hydrothermal spring; the glow is caused by the heat coming from the seabed. The team’s findings, detailed in a new paper published on Wednesday in Science Advances, suggests that this warm spot speeds up the hatching of the octopuses’ eggs, which improves reproductive success.
The researchers used remote cameras to study the behavior of the grapefruit-sized animals, and temperature and oxygen probes to understand the surrounding environment. They witnessed some well-known moments in the lives of octopuses: expectant mothers pouncing on males looking for a mate, scavengers trying to steal the eggs, and hatchlings “swimming the test” of shrimp and anemones waiting to attack, said Dr. Kahn. (The crew cheered whenever a newborn octopus successfully swam in the dark, he added.)
Using a mosaic of underwater images covering a region the size of several football fields, the team counted 6,000 octopuses in the garden. “And that’s only part of the area,” said Dr. Barry. They estimate the total population to be around 20,000. More than 80 percent of the octopuses at the site are nesting females, identified by their distinctive, protective posture.
Holding them aside with probes, scientists measured how the water around their eggs differed from the environment. They found that temperatures reached up to 52 degrees Fahrenheit at the sites where the females chose to brood, compared to just 35 degrees in the surrounding water.
“It’s a big thing for these eggs, because in the deep sea, one of the really big challenges is the cold,” said Dr. Barry. Cold temperatures slow the metabolism of cold-blooded animals, including embryonic growth rates. For this species of octopus, it can take anywhere from five to 10 years for eggs to fully develop in ambient water – but at this nursery, scientists found they hatch in less than two years on average .
The sooner the better, the team reasoned, when it comes to reproductive success. Less time spent as an embryo reduces the risks of being eaten by predators, or experiencing infections or injuries that lead to death. Because octopuses don’t eat while brooding — and die after breeding — they also suspect that faster hatching of eggs might make for a higher chance of survival, since the mother is less likely to lose energy. needed to maintain them.
This is the last hurrah of mothers, said Dr. Kahn: “They’re all about protecting those eggs.” She adds that meditating near a hot spring helps ensure that mothers’ final labors are successful.
The findings make sense to Michael Vecchione, a deep-sea cephalopod biologist at the National Oceanic and Atmospheric Administration who was not involved in the study. Dr. Vecchione, who saw the garden’s discovery in 2018, also speculated that octopuses use heat to accelerate embryo growth. “I’m not surprised that warm temperatures are beneficial to them,” he said. “And apparently, it’s starting to look like it’s a widespread phenomenon, even though nobody saw it until just a few years ago.”
Defined by Dr. Vecchione a similar gathering of octopuses, found in 2013 by another group of researchers, off the coast of Costa Rica. (However, at the time, scientists were not sure that the water surrounding a hydrothermal spring could be hospitable for the development of eggs. It was confirmed as an active nursery earlier this year.) And the team of Dr. Barry had already discovered another reproductive hot spot, which they named “Octocone,” five miles northeast of the Octopus Garden.
Wondering how common thermal spring nurseries are, Dr. Barry to organize more expeditions to other coastal areas. There is still much to learn about these ecosystems, said Dr. Kahn, including what attracts octopuses to gardens, whether, like sea turtles, they migrate back to breed in the same place they were born, and how mothers regulate their energy during brooding. .
“Until now, we’ve always thought that octopods were pretty solitary,” said Dr. Vecchione. “But the fact that it’s showing up more and more suggests that, at least for these deep-sea octopods, it’s an important life cycle that we don’t know about.”
For Dr. Barry, studying these ecosystems is important for both resource conservation and understanding the planet we live on. “We depend on the ocean in ways that most of us don’t understand,” he says, noting that it plays a role in climate and biodiversity as well as carbon cycling and storage. Learning about what’s under the sea — and how to protect it — “is worth the investment,” he added. “Because it can also make our lives better.”
