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 Laying eggs in the warmer water of geothermal springs accelerates the hatching process.

In the "Octopus Garden" (pictured) off the coast of California, some deep-sea octopuses lay their eggs in the warmer water of geothermal springs, speeding up embryonic development.

Octopuses in the deep sea 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 lay 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.

Thousands of deep-sea octopuses (Muusoctopus robustus) congregated on an area of seafloor about 3,200 meters below the surface, according to scientists working 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 from about 1.6° Celsius, this garden's growth was expected to be slow. According to marine scientist Jim Barry of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., embryonic growth in octopuses slows down at low temperatures. "When it gets really cold, down near zero, brood times are really extended," says the author.

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). M. robustus, which thrives in the frigid depths of the Octopus Garden, was a viable contender for the title, according to Barry. "At 1.6° C, it has an estimated brood period of more than 12 years."

From 2019 through 2021, Barry and his colleagues used a remotely driven vehicle to visit the Octopus Garden multiple times to verify what would be a record-setting stay of parenting. The researchers used cameras to track the development 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.

The scientists discovered that all of the egg clutches were bathed in moderately warm water (up to 10.5° C). The researchers discovered that female octopuses prefer to lay their eggs in streams of geothermally heated water. According to Barry, this revelation served as a red flag that these animals aren't the long-distance parents that people assumed they were. "We're almost positive these animals are reproducing at a rate significantly faster than you'd expect."

Deep-sea octopuses (Muusoctopus robustus) lay clutches of white fingers-like eggs.
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Barry and colleagues concluded that the moms only brooded for around 600 days, or about a year and a half, based on observations of mature 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 faster than projected. "They're slashing their parental care period by a significant amount of time."

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

Only a few other marine animals are known to seek warmer circumstances when 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 vital to various species as we keep looking," he says.

CITATIONS

J. Barry et al. Geothermal warm springs are incubators for deep-sea octopus reproduction. Ocean Sciences Meeting. February 28, 2022.

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