Yearslong mystery of deep sea ‘octopus garden’ off CA coast solved, researchers say

As researchers searched the ocean deep off the coast of California nearly five years ago, they came across something unexpected.

The researchers were exploring the foothills of the Davidson Seamount, about 80 miles southwest of Monterey, when they stumbled upon “shimmering waters,” which suggested the “region had previously unknown thermal springs,” the Monterey Bay Aquarium Research Institute said in an Aug. 23 news release.

But within those warm waters 2 miles below the ocean’s surface came something even more thrilling — thousands of octopuses, known as Muusoctopus robustus, researchers said.

“It sparked our curiosity too. What makes this location so special?” Jim Barry, a scientist with MBARI, said in a video from the institute. “Is it the food, the company or maybe something else the garden is providing?”

After 14 dives over three years to study the garden, the institute said it now has the answer to the spot’s appeal.

Thousands of octopuses, nicknamed pearl octopus for their similar appearance to pearls spread across the seafloor, migrate to the area with the sole purpose of reproduction, according to the institute.

Octopuses use the warm waters to brood their eggs, the institute said. The waters function as a natural incubator, where the octopuses’ eggs can hatch, in some cases, four times faster than when in typical deep sea conditions.

“The deep sea is one of the most challenging environments on Earth, yet animals have evolved clever ways to cope with frigid temperatures, perpetual darkness, and extreme pressure,” Barry said. “Very long brooding periods increase the likelihood that a mother’s eggs won’t survive. By nesting at hydrothermal springs, octopus moms give their offspring a leg up.”

Exploring the deep sea for answers

The institute said it used a “suite of advanced scientific instruments” to explore the octopus garden. With the advanced tools, scientists mapped part of the ocean garden to “centimeter-scale.”

Using high-resolution photographs, researchers said they counted nearly 6,000 octopuses clustered within a 6.2-acre area in the garden’s center.

Based on the total acreage of the garden, the institute said it estimates that there are at least 20,000 octopuses occupying the area.

“The octopus garden is the largest known aggregation of octopus on the planet,” the institute said.

Researchers said they also took “long-term observations” using a time lapse camera. This allowed them to capture the “behavior and changes in the community over a period of more than six months.”

The photographs showed the octopuses’ behavior, as well as that of predators and local scavengers, the institute said.

“The octopus garden supports a thriving community of life,” Barry said.

‘Final resting spot’

Through its research, the institute said it learned that both male and female pearl octopuses migrate to the area.

The females search for a warm place to deposit their clutches of about 60 eggs, the institute said.

The nests are “clustered in crevices bathed by hydrothermal springs where warmer waters flow from the seafloor,” according to the institute.

The mothers will then cover the eggs using their bodies, protecting the eggs from predators, the institute said.

They will not leave their side, living “off food reserves from her own tissues while tending to her developing eggs,” according to the institute.

As with other octopus species, pearl octopus are semelparous, meaning they reproduce one time and then die. Thus, the garden is many octopuses’ “final resting spot,” the institute said.

“Most females live until their eggs have hatched,” the institute said. “Sometimes, however, a mother octopus runs out of energy and dies before her eggs complete their development, exposing the developing eggs to greater risk.”

Carcasses of dead octopuses are moved away by nesting mothers, which become feasts for other sea creatures, according to the institute.

In the warm waters of the garden, the eggs will hatch in less than two years time, the institute said. In other areas of the deep sea, the eggs would take anywhere from five to eight years to hatch.

Questions remain

As the institute continues to study the garden, it said there are still a number of unanswered questions, like where the pearl octopuses go after hatching.

The institute said it would also like to answer “how this octopus species became adapted to breeding in thermal springs” and “how adult octopus find the thermal springs.”

Additionally, the institute said it plans to study the advantage of breeding in the hydrothermal springs over other areas.

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