WASHINGTON (AP) — Most octopuses lead solitary lives. So scientists were amazed to find thousands of octopuses huddled, protecting their eggs on the ocean floor off California’s central coast.
Now researchers may have solved the mystery of why these pearl octopus congregate: The heat seeping up from the base of an extinct underwater volcano is causing their eggs to hatch faster.
“There are clear benefits to sitting in this natural hot tub,” said Janet Voight, an octopus biologist at the Field Museum of Natural History in Chicago and co-author of the study, published Wednesday in Science Advances.
The researchers calculated that the heated nest site more than halved the time it took for eggs laid there to hatch, reducing the risk of them being eaten by snails, shrimp and other predators.
The breeding ground, which the scientists called an “octopus garden,” was first discovered in 2018 by researchers from the Monterey Bay National Marine Sanctuary and other institutions. The team used a remote underwater vehicle to film the crowd of nearly 6,000 octopuses nesting at a depth of 2 miles (3.2 kilometers).
The octopus—about the size of a grapefruit—perched atop their eggs, which lay on rocks warmed by water seeping up from the seafloor.
“It was completely unbelievable – we suddenly saw thousands of pearly octopuses, all of them upside down, with their feet in the air and moving around. They pushed away potential predators and flipped their eggs,” for an even flow of water and oxygen, said marine biologist Andrew DeVogelaere of the National Oceanic and Atmospheric Administration, a co-author of the study.
Only the hazy glare of escaping hot water meeting the frigid sea alerted the researchers to the hydrothermal seep. But they still weren’t quite sure why the octopus had gathered there.
For three years, scientists monitored the site to understand the hatching cycle, recording both the developmental stage of the eggs in 31 nests and the inevitable death of octopus mothers.
“After the young emerge from the nest and swim immediately into the dark, the mothers, who never left their nests and never seemed to feed while nesting, soon die,” said James Barry, a biologist at the Monterey Institute and co. -author. author of the study.
The researchers found that the eggs at this location hatch after about 21 months — much shorter than the four years or more it takes for other known deep-sea octopus eggs.
“Usually, colder water slows down metabolism and embryonic development and extends lifespan in the deep sea. But here in this place, heat seems to speed things up,” said Adi Khen, a marine biologist at the Scripps Institution of Oceanography, who was not involved in the study.
Mike Vecchione, a zoologist at the Smithsonian National Museum of Natural History who was not involved in the study, praised the researchers’ tenacity “to collect so much detailed data on such a remote location.”
Such octopus gardens “could be widespread and very important in the deep sea, and we knew very little about them before,” he said. “There is still so much to discover in the deep sea.”
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