Thermal springs from an extinct underwater volcano make the “Octopus Garden“ on the deep seafloor off the Central California coast a paradise for the animals‘ mating and nesting

An aggregation of female pearl octopus (Muusoctopus robustus) nesting at the Octopus Garden, located near Davidson Seamount off the Central California coast at a depth of approximately 3,200 meters. Source: MBARI

In 2018, researchers observed thousands of octopuses nesting on the deep seafloor off the Central California coast. The discovery of the so-called “Octopus Garden” captured the curiosity of millions of people around the world. Now, a team of scientists confirmed that the deep-sea animals migrate to the site to mate and nest: At this nursery, warmth from deep-sea thermal springs accelerates the development of their eggs.

The Garden off the Central California coast is one of only a handful known such deep-sea octopus nurseries. It has the largest known aggregation of these animals on the planet—researchers counted more than 6,000 animals in a portion of the site and expect there may be 20,000 or more in total.

The Californian Octopus Garden is located 3,200 meters (10,500 feet, or about two miles) below the ocean‘s surface on a small hill near the Davidson Seamount, an extinct underwater volcano 130 kilometers (80 miles) southwest of Monterey, California. The site is full of Muusoctopus robustus — a species researchers nicknamed the pearl octopus because, from a distance, nesting individuals look like opalescent pearls on the seafloor.

Over the course of 14 dives with a remotely operated vehicle, a research team from Monterey Bay Aquarium Research Institute (MBARI) learned that the location must be ideal for mating and nesting: The presence of adult male and female octopus, developing eggs, and octopus hatchlings indicated that the site is used exclusively for reproduction. The team did not observe any intermediate-sized individuals or any evidence of feeding.

When researchers from the National Oceanic and Atmospheric Administration (NOAA) and Nautilus Live had first discovered the Octopus Garden, they observed “shimmering” waters. This phenomenon occurs when warm and cool waters mix, suggesting the region had previously unknown thermal springs.

New investigation confirmed that the animals‘ nests are clustered in crevices bathed by those springs where warmer waters flow from the seafloor.

The ambient water temperature at 3,200 meters (10,500 feet) deep is 1.6 degrees Celsius (about 35 degrees Fahrenheit). However, the water temperature within the cracks and crevices at the Octopus Garden reaches nearly 11 degrees Celsius (about 51 degrees Fahrenheit).

Octopuses are ectotherms or cold-blooded animals. Their egg incubation time with the embryo development depends on the water temperature.

“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. By nesting at hydrothermal springs, octopus moms give their offspring a leg up,” said MBARI Senior Scientist Jim Barry, lead author of the study.

The massive number of octopus in one area attracts both predators and scavengers. Like most other cephalopods, pearl octopus die after they reproduce. A rich community of invertebrates undoubtedly feeds on unhatched eggs, vulnerable hatchlings, or adult octopus that have died.

The study was published in Science Advances by a team of authors from Monterey Bay Aquarium Research Institute (MBARI), NOAA’s Monterey Bay National Marine Sanctuary, Moss Landing Marine Laboratories, the University of Alaska Fairbanks, the University of New Hampshire, and the Field Museum.

Source: Monterey Bay Aquarium Research Institute (MBARI)

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(28.08.2023, USA: 08.28.2023)