An Octopus's Garden

October 1, 2023
By Tara Haelle

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Thousands of brooding octopuses have been found where warm water seeps out from the seafloor. The warmer temperatures accelerate the development of their offspring. Credit: Monterey Bay Aquarium Research Institute (MBARI).

It’s no longer just a popular Beatles song—off the coast of central California, nearly two miles under the sea, is a “garden” of at least 6,000, and possibly up to 20,000, purple octopuses known to scientists as Muusoctopus robustus. Scientists first discovered the site about five years ago but needed time to investigate what led so many octopuses to congregate around Davidson Seamount, an extinct underwater volcano about 80 miles southwest of Monterey, California.

The spot, now named the Octopus Garden, has attracted a consortium of octopuses and they’re nearly all females that are guarding their egg clutches. The underwater volcano may be defunct, but warm water seeps out from the seafloor there, raising the ambient water temperature from about the 1.6° C (35° F) of the surrounding water to around 11° C (51° F). That warmth speeds up octopus embryonic development, reducing the time necessary to brood the eggs from around 4.5 years for the typical deep-sea octopus to only about 1.8 years. The scientists speculate that the shortened brooding time may also improve the chances that baby octopuses survive, since the mothers and eggs spend less time vulnerable to predators.

Octopuses are usually loners that avoid other octopuses, but these moms are so focused on incubating their eggs that they ignore the thousands of incubating moms around them—and even the robot-mounted cameras the researchers use to get up-close looks at the cephalopods. The researchers now wonder how many other warm, deep-water nurseries might exist near seamounts and hydrothermal vents. So far, they know of three other deep-sea octopus nurseries—another one off California’s coast and two off Costa Rica’s coast, but they’re looking for more.