Two miles under the ocean’s surface, in one final act, a lavendar-colored pearl octopus about the size of a grapefruit selects a nesting site. After gluing about 60 sausage-shaped eggs to that perfect rock, she positions her mantle — her bag-shaped body — atop her clutch of eggs, then drapes her arms backward around herself, tucking in both her babies and her vital organs for the long haul.
For the next several years, the expectant mother will brood — incubate her eggs — in the black, frigid water, battling predators but never abandoning her eggs. Not even to forage. She’ll expend every ounce of energy she’s got protecting that nest. And then she will die. With luck, she’ll make it until her eggs are fully developed and, as her body is scavenged by a hungry anemone or a shrimp, her hatchlings will emerge and disappear into the deep sea. And the circle of life will continue.
In 2018, deep-sea researchers stumbled upon a group of thousands of brooding pearl octopus (Muusoctopus robustus) at Davidson Seamount — an extinct underwater volcano just 80 miles southwest of Monterey. It was an astounding aggregation of the normally solitary creatures.
Wednesday, in the journal Science Advances, researchers confirmed that the “Octopus Garden” is the largest known aggregation of octopus on Earth, with nearly 6,000 octopus in one 6-acre portion of the site, and an estimated 20,000 or more total. The team, which includes local researchers from the Monterey Bay Aquarium Research Institute, NOAA’S Monterey Bay National Marine Sanctuary and Moss Landing Marine Laboratories, also reported that pearl octopus migrate to the site for the sole purpose of reproducing and with good reason.
Deep-sea thermal springs warm the water from near-freezing to around 50 degrees. By the team’s calculations, the warmer temps shorten the brooding period from five or more years to less than two, reducing the time moms have to fend off predators and giving the eggs a leg up on survival.
The results of the three-year study, conducted with high-tech robots and other custom equipment, arrive as researchers are discovering new deep-sea nurseries across the globe.
“The importance of studies like this can’t be understated,” said Charisse Du Preez, head of Fisheries and Oceans Canada’s deep-sea ecology program. Du Preez’s team recently discovered an octopus nursery near Canada, but she was not involved in this study. “These scientists are showing us what’s at stake if we go ahead with activities like deep-sea mining. I think the timing couldn’t be more important.”
Diving for visual data in the deep, dark sea
Jim Barry, senior scientist at MBARI and lead author of the study, said when they explored the base of Davidson Seamount in 2018 and first discovered the Octopus Garden, they had no detailed maps to orient themselves.
“If you don’t have a good map, it’s like having somebody blindfold you, take you somewhere on a moonless night and put you on a hillside with a flashlight,” he said. One goal of this three-year study was to fix that problem.
With MBARI’s underwater robots — a mapping autonomous underwater vehicle and their remotely operated vehicle (ROV) Doc Ricketts — the team mapped the Octopus Garden down to the centimeter.
Doc Ricketts is named after marine biologist Ed Ricketts, who inspired the character Doc in John Steinbeck’s Cannery Row.
The ROV team is also equipped with all kinds of lasers, robotic arms and high-resolution photography equipment. MBARI is home to a highly skilled team of engineers and submersible vehicle pilots. Between April 2019 and August 2022, over 14 visits, the team landed Doc Ricketts at the Octopus Garden to measure water temperature and oxygen levels in nests and get close-up videos of mothers and their eggs.
With their new maps, the team could even return to individual nests to monitor them over time.
“It sounds simple,” Barry said, but it’s not. They had to drive a ship out 100 miles from Moss Landing, use GPS to find the right site, send the ROV down 2 miles underwater where GPS doesn’t work, then use an acoustic navigation system to crawl around the ocean floor trying to find the right spot. “It’s kind of tricky,” he said, “but with the advances in technology and the improvements in mapping that we have…we drive right up to the spot and go yep, that’s the spot.”
They’d confirm they had the right octopus by identifying her unique scars from battles with predators. With this approach, they calculated that eggs in the nursery complete their 20-stage development process and hatch in under two years.
Time-lapse data, collected by a camera anchored at the site and programmed to take an image every 15 minutes for six months, confirmed that number. It also showed that the deep sea ecosystem was thriving.
“In that one six-month period we saw everything octopuses do,” Barry said. “We saw females brooding, males coming in and mating with the females, hatchlings leaving, females dying before their eggs hatched, predators jumping on carcasses floating around…you think of the deep sea as being super slow, and things do happen slowly there. But this octopus garden is full of life — it’s this cycle of brooding, birth and death just playing out right in front of you. It’s this nexus of activity and the intersection of the beginning and the end of their lives. To see that all come together has just been astounding for me.”
Other octopus incubators
The Octopus Garden is one of only five known deep-sea octopus nurseries in the world. The Octocone, discovered in 2019, is another pearl octopus nursery located just 10.5 miles northeast of the Octopus Garden on a volcanic cone near Davidson Seamount.
Costa Rica is home to two additional nurseries. In 2013, international researchers discovered the nursery of a new species of octopus at the Dorado Outcrop, a hydrothermal spring about 100 miles off Costa Rica’s Pacific coast. It was actually the first deep-sea octopus nursery to be discovered, but it was smaller than the Octopus Garden — less than a football field in size, with only a few hundred octopus. While all of the octopus there were in brooding position, the eggs weren’t viable.
When the team returned this June — 10 years later — the octopus were still there. And this time the eggs were viable. On that same trip, they discovered a second Costa Rican nursery, also. Both nurseries are smaller than the Octopus Garden — less than one football field in size, with only a few hundred octopus — but both nurseries are near a hydrothermal springs.
“That’s what’s so special about these places,” said Jorge Cortés Núñez, a researcher and biology professor emeritus at the University of Costa Rica and co-chief scientist of the recent expedition who was not involved in the new study. ”Octopus are solitary, but in these places (near hydrothermal springs) they are aggregated.”
Hydrothermal springs are different from the deep-sea hydrothermal vents you may have heard of — the ones that spew geysers of water superheated by magma near the Earth’s crust to temperatures over 700 degrees.. There’s still a heat source somewhere, but instead of gushing, the water gently seeps through the fractured and porous seafloor, bathing the crevices in water that’s warm for the deep sea, but not scalding.
“These are just little tiny springs that are perfect for these little octopuses,” Barry said.
The fifth nursery, also discovered this June, is different. It’s a cold seep — a site where methane gas seeps through fissures in the ocean floor, but temperatures at the site don’t change. That nursery is about 40 miles offshore of Vancouver Island.
The discovery of the fifth nursery adds a question about aggregation — there was no heat but they still chose to sit right next to each other. Heat might be one benefit, but could there be another? Du Preez thinks it’s worth considering. In Canada, she observed octopus physically punching crabs that got too close to their nest. She suspects that there’s power in numbers. “If you’re gonna be getting in a gang fight at the bottom of the ocean,” she quipped, “wouldn’t you want 200 of your buddies around throwing arms at the same time?”
A blueprint for future studies
The recent flurry of nursery discovery has been fueled by advances in technology and engineering, and, with a federally protected area to study, the Central Coast researchers are in a prime spot to take advantage.
“We’re really lucky — we have this nationally significant area, and then we have this engineering and science powerhouse in our backyard that wants to figure out better ways of understanding it and exploring it,” said Andrew DeVogelaere, a research ecologist for NOAA’s Monterey Bay National Marine Sanctuary and co-author of the new study. “MBARI has international experts in science and they have the best engineering and technology in the deep sea in the world.”
Núñez called the scale of the new study “very impressive.”
“In Monterey it’s right there in their backyard, and they have all the equipment at MBARI,” he said, so they could follow individuals and track changes over time in great detail. “We cannot do that.” Núñez’s research depends heavily on international collaborations and the availability of other nations’ research vessels. They can study sites for a few months at a time, but not for years.
But the new research can serve as a roadmap for Núñez’s work. “We’re going to look into the details so that (on to the site) we can go back and say OK, we should be measuring something that we didn’t think about,” he said.
Du Preez said that discovering five separate octopus nurseries across the globe in just a few years shows is not just a localized phenomenon — there are probably more. Studies like this help international researchers figure out where to look and what to do if they find a nursery.
“We can’t go out and search everywhere,” Barry said. “We have to focus our deep-sea exploration and spend the money wisely.”
Still full of surprises
This new study shows that octopus at hydrothermal vents impact more than their own little hotspots — they drive whole ecosystems with undefined boundaries.
“Historically, we’ve focused on hydrothermal vents and cold seeps and those crazy animals that exist at these extreme places and do these wackadoo things,” said Du Preez, “but studies like this show us that it’s not just that alien world.
“When you think about the magnitude of octopus that Jim (Barry) and his team found,” Du Preez said, “and the number of offspring that that site is putting out, and how widely distributed that octopus is, it’s hard to actually wrap your head around how much that site is probably influencing the larger ocean. The Pacific Ocean is massive, and its at depths that these octopus can migrate to — it’s all interconnected.”
Barry and DeVogelaere’s teams have more work to do at Davidson Seamount. They plan to learn more about the geology and the plumbing of the hydrothermal springs, more about the carbon these nurseries contribute to the deep-sea ecosystems and more about the octopus themselves — how octopus moms decide where to allocate their energy and how they fight predators, where hatchlings go after they’ve hatched and how they find their way back.
But to understand the global scale of the nurseries’ impacts, they’ll keep spending time with individuals. Du Preez said it’s amazing to study creatures whose mysterious lives in the deep sea are so cryptic and yet so relatable.
“We all have moms, we all know sacrifice for the next generation,” she said. “We think of that as so human, and then 3,000 meters down into the deep we’re finding animals that remind us of that.”
Barry finds it hard to describe the experience of getting to know individual animals over time.
“Those are beautiful and just amazing to me, and I love working on them, but there’s something about these octopus that you can relate to, on a personal level that you can’t relate to with a coral,” he said. “This might be my favorite project…it’s certainly the most compelling.”
DeVogelaere hopes the work will motivate the next generation of marine scientists. “A lot of people think that maybe the age of exploration is done, but there’s still new animals to be found and new places to explore and there’s actually, I believe, a real need to know and understand them,” he said.
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