A new study confirmed that an underwater “Octopus Garden” in the Pacific Ocean off the coast of the Central Valley, discovered in 2018, is home to the largest known aggregation of octopus on the planet — and the research, conducted over the past five years, also reveal why that is.

In 2018, researchers on an expedition to Davidson Seamount, an extinct underwater volcano about 80 miles southwest of Monterey, first observed a unexpectedly large community of “Muusoctopus robustus,” also known as the pearl octopus, on the ocean floor nearby, according to the research group's press release. While scientists believed that it was one of only a handful of known deep-sea octopus nurseries, they didn’t know just how many octopus there were.

Several groups, including the Monterey Bay Aquarium Research Institute and Moss Landing Marine Laboratories, came together to organize more than a dozen deep-sea dives using a custom-built remotely operated vehicle (ROV) equipped with a 4K camera, as SFGATE reported. The equipment reportedly enables researchers to identify each individual octopus, which are about the size of grapefruits, and track their habits. They found that most of the octopus were upside down, inverting their arms and folding them around their bodies — an indication of pearl octopus mothers protecting their eggs (called “brooding”).

Image via Monterey Bay Aquarium Research Institute.

More observation found only adult male and female octopus, developing eggs, and hatchlings at the site, which is about two miles below the ocean’s surface, suggesting that it was exclusively used for reproduction. The question of “why” remained.

They were able to determine that a deep-sea thermal springs just beneath the crevices of the site provided warmth otherwise unavailable at the depths of the ocean floor. The temperature in these crevices is about 51 degrees Fahrenheit, compared to the rest of the temperature in the abyss, which are about 35 degrees. This warmth apparently accelerates the development of the octopus eggs, reducing the incubation period, and enhancing the chances of hatchling survival.

Image via Monterey Bay Aquarium Research Institute.

As the research revealed, deep-sea octopuses typically experience extended incubation periods due to the cold temperatures of their habitat, which slow down embryo development. In the freezing abyss, pearl octopus eggs were initially projected to take five to eight years or more to hatchl but the 4K camera closely observed nesting mothers, tracking their unique markings, and found that contrary to expectations, the eggs hatched in under two years, as the warmth from thermal springs accelerated the metabolism of female octopuses and their broods.

The octopus hotspot still attracts predators and scavengers — in fact, octopus mothers die after reproducing, so a thriving community of invertebrates lives alongside the nesting females, feeding on the weak hatchlings and dying mothers.

Image via Monterey Bay Aquarium Research Institute.

This key discovery holds important implications for understanding the deep-sea ecosystem and underscores the fragile interplay between these creatures and their environment, the researchers say. As senior scientist Jim Barry puts it, "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."

They believe that the Octopus Garden's role as a sanctuary for reproduction and a haven for scavengers in the abyssal depths shows the need for the protection of such unique and vital habitats as human impact extends further into the oceans.

You can watch the research group's video about the discovery and see more of the Octopus Garden here.

Feature image of the Octopus Garden via the Monterey Bay Aquarium Research Institute.