Scientists Discover Strange Breeding Behavior of Deep-Sea Octopus Moms

Octopuses in the deep water off the coast of California are reproducing at an unprecedented rate.

Researchers report on February 28 at the virtual 2022 Ocean Sciences Meeting that the creatures deposit their eggs near geothermal springs, and the warmer water speeds up embryonic development.

Because of this reproductive ruse, octopus mothers only have to brood for two years instead of the usual 12.

Octopus Gathering

Thousands of deep-sea octopuses (Muusoctopus robustus) converged on an area of seafloor approximately 3,200 meters below the surface, according to scientists operating off the coast of California in 2018. The place was dubbed the Octopus Garden because many of the grapefruit-sized critters were females brooding clutches of eggs.

However, with water temperatures ranging about 1.6° Celsius, this garden's development was expected to be slow. According to marine scientist Jim Barry of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., embryonic development slows down in octopuses at low temperatures. "When you get freezing, down around zero, that's when brood periods go incredibly protracted."

A separate species of an octopus living in warmer water holds the record for the longest brood time of any animal, a little over four years (SN: 7/30/14). According to Barry, M. robustus, which thrives in the frigid depths of the Octopus Garden, was a viable candidate for the title. It has a projected brood period of nearly 12 years at 1.6° C.

Visiting the Octopus Garden

From 2019 through 2021, Barry and his colleagues used a remotely driven vehicle to visit the Octopus Garden many times to verify what would be a record-setting stay of motherhood. The researchers used cameras to track the growth of the octopus eggs, which resemble white fingers.

The researchers also gently moved dozens of octopuses aside and assessed the water temperature in their nests using one of the submersible's robotic arms. They also discovered that all egg clutches were bathed in moderately warm water (up to 10.5° C). The researchers found that female octopuses prefer to deposit their eggs in streams of geothermally heated water.

This discovery served as a red flag that these animals aren't the long-distance mothers that people assumed they were. "We're almost positive these creatures are reproducing at a rate significantly faster than you'd expect."

Barry and colleagues concluded that the moms only brooded for around 600 days, or about a year and a half, based on observations of maturing eggs.

According to Jeffrey Drazen, a deep-sea biologist at the University of Hawaii at Manoa who was not involved in the study, this is far quicker than projected. "They're slashing their parental care period by a significant amount of time."

Incubation Period

Shorter incubation times imply fewer eggs are likely to be eaten by predators, which is an evolutionary benefit to searching out warmer water. And these octopuses appear to be aware of it, according to Barry. "We think they're using that heat energy to help them reproduce more successfully."

Only a few other marine creatures are known to seek warmer conditions while mating, such as icefish in Antarctica's Weddell Sea (SN: 1/13/22). But, according to Drazen, other species are likely to do the same. Finding them and their nesting habitats in the vastness of the deep ocean is the issue. "I'm sure we'll keep uncovering incredibly intriguing areas that are crucial to various species as we keep exploring," he adds.

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