A steadfast little octopus living in the deep waters of Monterey Bay has set an extraordinary record of animal motherhood, laying her clutch of eggs and brooding them nonstop for 53 straight months – apparently without pause for food or rest.
No creature in the world, large or small, has ever approached such a feat, say biologists who watched over the octopus with cameras in an unmanned submarine from Monterey Bay Aquarium Research Institute.
The deep-water octopus was a small one, with a mantle barely 8 inches from stem to stern. But she made up in staying power what she lacked in size, said Bruce Robison, the institute biologist who observed the mother again and again as she protected her eggs on a rock in the Monterey Submarine Canyon.
Robison has been studying the ecology of the canyon’s mid-level waters for 25 years. He was in the midst of such work seven years ago when he spotted a female octopus moving slowly across the ocean floor toward a rocky outcrop 4,600 feet beneath the surface where he’d noticed other females brooding their eggs.
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He was aboard a research vessel towing an unmanned submarine known as a remotely operated vehicle, which is equipped with specialized observation cameras and sensors.
A distinct pattern of scars on this female’s mantle identified the octopus, and a month later when Robison returned with his underwater vehicle he spotted her again, this time guarding a clutch of newly laid eggs attached to the same rock.
“This was a chance to watch the whole brooding process,” Robison said. “It was a fluke. No one before ever had a chance to see anything like it, so it was kind of bootleg science, but we decided to watch her again and again.”
And he and his team did. They sent their tethered vehicle down to the same rock on 18 visits for what turned out to be a 4 1/2-year mission.
Octopus eggs develop extraordinarily slowly in cold water – it was 37 degrees where the eggs were laid – and this mother was on duty every time the scientists checked in.
“We measured her with lasers,” Robison said, “and each time we saw her eggs growing larger and larger until we could see her babies developing inside the transparent eggs. We could watch her sweeping water over them with her arms to carry oxygen in the fresh seawater into their permeable egg cases, and we watched her brushing silt away to keep the eggs clear.
“During that whole time we never saw her leave the eggs once,” said Robison, whose team would watch the octopus closely for an hour or more each time they visited her rock. “We never saw her eat anything, and she paid no attention to the crabs and shrimp swimming by, except when she pushed them away with her arms because they were predators.”
The octopus even ignored proffered chunks of crab dangled from the unmanned sub, Robison said.
An octopus mother’s mantle in this species is normally a pale purple, Robison said, but as the months went by this mother’s skin sagged and turned white. Her mantle shrank and her eyes grew cloudy. “She just looked really old,” he said.
On Robison’s final observation, the mother was gone, and he never saw her again. The eggs, which she had attached to the face of the rock, were now only empty cases – each one about the size of a shrunken olive.
He never saw the hatchlings, but he counted the egg cases and figured there must have been 160 babies, all of which had swum off.
Evolution has given a clear advantage to this deep-sea octopus species, known scientifically as Graneledone boreopacifica, Robison said. By the time the eggs hatch, the young octopuses are fully developed and able to swim away and hunt for small prey on their own, he said.
The mother’s brooding time exceeded that of all other animals known to science, Robison said. Other octopus species are known to brood their eggs for only a few months. Until now, the longest known brooding time in the animal world was 3 1/2 years for the frilled shark and 21/2 years for the black baltic salamander, records show.
For the mother octopus, an empty nest is the end, Robison noted in a scientific report on the episode that was published Wednesday in the journal PLOS ONE.
“The ultimate fate of a brooding female octopus,” he wrote, “is inevitably death.”