Here’s why thousands of octopuses gather at the ‘Octopus Garden’

Underwater cameras and other tools delved into this pearl octopus mystery

a photo of the seabed where numerous octopus are gathering, most of them are sitting upside down with tentacles curled around themselves and their eggs

Thousands of pearl octopus gather at the Octopus Garden to lay their eggs. Mama octopuses like these sit upside-down on the seafloor with their arms wrapped around themselves and their eggs to guard their offspring.

© 2019 MBARI

The world’s largest known group of octopuses can be found in a place called the Octopus Garden. It’s tucked against a seafloor hill off the coast of California. Here, thousands of pearl octopuses (Muusoctopus robustus) gather to breed. Scientists have wondered for years what drew so many pearl octopuses to this spot. Now, underwater cameras and other tools have revealed the answer. Researchers shared the work August 23 in Science Advances.

Image: The words “Wild Things: A Graphic Tale” are written in green block letters. A toucan perches on the W in ‘Wild,’ a jaguar sleeps atop the T in ‘things,’ the letter S in ‘things’ is a snake, and other animals surround the text.
A purple octopus splays its arms across the rocky seafloor. Text: Secrets of the Octopus Garden. Written by Maria Temming, illustrated by JoAnna Wendel.
Text (above image): This is the Octopus Garden, the largest known group of octopuses in the world. Nestled on a rocky seafloor hill off the coast of California, it lies about 3.2 kilometers (2 miles) below the ocean’s surface. Image: Purple octopuses, both upright and upside-down with their arms wrapped around their bodies, are scattered across a rocky, bumpy stretch of seafloor. The seafloor is also spotted with yellow anemones, orange sea stars and other critters. Inset: A map shows the location of the Octopus Garden off the coast of California, south of San Francisco and Monterey.
Image: A purple octopus rests upside-down on the seafloor with her arms wrapped around herself and a cluster of white, sausage-shaped eggs beside her. Text (below image): “It’s just kind of this magical place in the dark, cold waters of the deep sea,” says James Barry. He’s a marine biologist at the Monterey Bay Aquarium Research Institute in California. At the Octopus Garden, thousands of pearl octopuses, each about the size of a grapefruit, gather to mate and nest.
Text (above image): Since it was discovered in 2018, scientists have wondered why pearl octopuses chose this spot for their nursery. To find out, Barry and his team drove a remote-controlled robot down to the Octopus Garden 14 times over three years. Image: A boat floats atop the ocean. Connected to the boat is a cable, which runs down through the water to a robot equipped with arms and cameras. The robot’s camera is peering at purple pearl octopuses clustered on the seafloor among yellow anemones. Inset: A view of inside the ship shows a scientist peering at several screens, which show the underwater robot’s views of the octopuses on the seafloor.
Text (above first image): “You can drive [the robot] right up to them,” Barry says. “We hold cameras literally eight inches away. … They just don’t seem to care.” First image: A camera hovers inches away from a pearl octopus sitting on the seafloor with its arms folded up around its body. Text (above second image): The robot stuck probes in and around octopus nests to measure temperature and other water conditions. Mama octopuses didn’t like that, Barry says. “They just are tenaciously holding on and covering those eggs.” Second image: a gray, cylindrical probe pokes into the cluster of eggs tucked against a mother octopus’s side on the seafloor.
Text (above image): The researchers also left a camera on the ocean floor that snapped pictures every 20 minutes for about six months. Image: A large metallic tripod stands on the seafloor, holding a camera. The camera is pointed at a group of octopuses sitting upside-down on the seafloor to guard their nests of eggs.
Text (above image): The observations revealed that octopuses nested near cracks and crevices where warm water seeped out of the seafloor. Image: A diagram of the seafloor hill that holds the Octopus Garden shows how warm water seeps up through the hill to the seafloor area where the octopuses are clustered. In this area, a thermometer shows that the water temperature is about 5 degrees Celsius. Another thermometer a short distance from the Octopus Garden shows that the water there is only 1.6 degrees Celsius. Text (below image): In these hotspots, waters were warmer than 5 degrees Celsius (41 degrees Fahrenheit) on average. Surrounding waters were only a chilly 1.6 degrees Celsius (35 degrees Fahrenheit).
Text (above image): “For octopuses that live in the deep sea, the colder the water is, the longer it takes them to brood their eggs,” Barry says. The extra warmth may help eggs hatch faster. Image: A purple pearl octopus with its arms sprawled out drifts in dark waters above a graph. The graph shows how the brood period for octopus eggs (measured in years) declines as water temperature increases (measured in degrees Celsius). Text (below image): Eggs in the Octopus Garden’s hotspots hatched in less than two years. In colder waters nearby, eggs would probably take at least five years to hatch.
Image: A cluster of octopus eggs sits exposed on the seafloor. A red shrimp hovers near the eggs, ready to attack. A speech bubble coming from the shrimp says, “Yummy!” Text (below image): Hatching faster leaves less time for octopus eggs to get injured, sick or eaten. That probably boosts baby octopuses’ odds of survival at the Octopus Garden, which is prowling with shrimp, snails and other animals with a taste for octopus eggs.
Mama octopuses usually die after their eggs hatch. So after hatching, the babies don’t stick around. “They swim off into the dark,” Barry says. Where they go remains a mystery. Image: Seven baby pearl octopuses drift apart in dark ocean waters. The baby octopuses are smaller and thinner, with shorter arms, than their parents.

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Maria Temming is the Assistant Managing Editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

JoAnna Wendel is a freelance science writer and cartoonist in Portland, Ore. She loves to make comics about all types of science, but she especially loves drawing planets, invertebrates and sea creatures. When she's not drawing, JoAnna is probably reading, hiking or hanging out with her cat, Pancake.

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