The Editor says: Think there's nothing living in the deep sea? Scientists have discovered 20,000 pale-purple Pearl Octopuses on the seafloor 3,200 metres deep off the coast of California — and the sight looks just like an underwater garden. Research suggests the octopuses chose this spot because nearby hydrothermal vents raise the water temperature, speeding up egg development and shortening incubation times, which dramatically improves the survival rate of hatchlings. But why don't the eggs get "cooked" by the vents? Follow along with Bru to find out! <Full article reprinted from the Environmental Information Center, compiled from international sources; translated by Mingshan Xie; reviewed by Zuling Xu>
Octopuses are typically solitary creatures, yet a group of pale-purple Pearl Octopuses (Pearl Octopuses; Muusoctopus robustus) — roughly the size of a grapefruit — have gathered about 3,200 metres beneath the ocean surface off the California coast, forming an "octopus garden" spanning approximately 333 hectares.
More than 20,000 Pearl Octopuses have congregated roughly 3,200 metres beneath the ocean surface off the California coast, forming an "octopus garden" covering 333 hectares. Image credit: MBARI
Warm Submarine Volcanic Springs — the Perfect Spawning Ground for Pearl Octopuses
According to The Guardian, the octopus garden was first discovered in 2018 by a research team from the Monterey Bay Aquarium Research Institute (MBARI). Their initial hypothesis was that nearby submarine volcanic vents warm the surrounding water, accelerating egg incubation and drawing Pearl Octopuses to congregate in the area.
The research team spent more than three years conducting over ten remotely operated vehicle (ROV) dives to the seafloor, ultimately confirming their hypothesis. Each female Pearl Octopus lays approximately 60 eggs, attaching them to exposed rock. The mothers guard their eggs tirelessly throughout the entire incubation period.
There are at least four known deep-sea octopus aggregation sites around the world. MBARI scientists estimate the total number of octopuses at this site to be as high as 20,000, making it the largest known gathering of its kind.
According to Scientific American, in waters where the temperature is only 1.6°C, octopus eggs incubate very slowly — taking a minimum of five years, and in some cases as long as 13 years. The colder the water, the slower the incubation. In the area where these octopuses congregate, however, water temperatures range between 5°C and 10°C, allowing hatchlings to emerge in under two years.
During incubation, octopus eggs — and the mothers themselves — are vulnerable to early death from predation, infection, and other factors. A shortened incubation period therefore greatly increases the survival rate of hatchlings.
Deep-sea hydrothermal vents expel plumes of superheated fluid and are classified as either "black smokers" or "white smokers" based on the colour of the emissions. MBARI benthic ecologist James Barry explains that the water at this site is nowhere near as hot as that found at black smoker vents, and is therefore not hot enough to cook the octopus eggs.
Female Pearl Octopuses are only about the size of a grapefruit and display a pale-purple colouration. Each individual lays approximately 60 eggs, affixed to exposed rock. Image credit: MBARI
The Octopus Garden Creates an Underwater Oasis
The research team found that the octopus garden also creates an oasis for other marine life. Male Pearl Octopuses die shortly after mating. Once the eggs hatch, the mothers also perish. Other deep-sea creatures — including fish, shrimp, sea stars, and snails — feed on the carcasses, giving rise to a thriving ecosystem.
The deep sea harbours many treasures: not only metals such as copper, cobalt, nickel, and manganese, but reportedly also rare earth elements including yttrium, as well as substantial deposits of gold, silver, and platinum — all of considerable strategic value. Many nations are eyeing the enormous potential profits from deep-sea mining. Although this particular octopus garden lies within the Monterey Bay National Marine Sanctuary and is relatively protected, Barry warns that many as-yet-undiscovered octopus breeding grounds are under threat from bottom trawling and deep-sea mining. We must cherish these marine treasures and resist the urge to simply bulldoze the seafloor.
Editor in charge: Jenny Tsai
References
- The Guardian (23 August 2023), Discovered in the deep: an octopus's garden in the shade
- Scientific American (23 August 2023), The Hot Secret behind a Deep-Sea 'Octopus Garden'
- MBARI (23 August 2023), Scientists solve mystery of why thousands of octopus migrate to deep-sea thermal springs
Republished with permission from the Environmental Information Center. Original title: Scientists Discover Deep-Sea "Octopus Garden" off California — Over 20,000 Octopuses Gather at Hydrothermal Vents to Create Underwater Oasis
