Led by Bruce Robison, a team of MBARI researchers has spent 25 years diving into the depths of Monterey Canyon to survey deep-sea life. In May 2007, a female Graneledone boreopacifica octopus was found clinging to rocks about 4,600 feet below the surface.
During 18 dives over four and a half years, the researchers observed the same octopus (which was distinguishable because of some unique scarring) slowly incubating a single clutch of eggs. According to the researchers, she appeared to never leave her brood, and was never seen to eat anything.
When the researchers found empty egg capsules in her place—indicating that her young had finally hatched—they estimated that her clutch had held about 160 eggs. Many shallow-sea octopods can hatch thousands of young after only months of incubation. But despite the time invested in a relatively small number of eggs, Graneledone boreopacifica is one of the most abundant deep-sea octopods in the Pacific.
This isn’t the first sign that Graneledone boreopacifica might use some unique reproductive strategies. Janet R. Voight, associate curator of zoology at The Field Museum, did her own research on the deep sea octopus in 2002. Voight, who wasn’t involved in the PLOS ONE study, found the species to produce the most developmentally advanced octopods ever seen—even though the ones she examined were hatched prematurely.
“They were 55 millimeters in length, which is about as big as a shallow water octopus would be at three months of age,” Voight said. “So we figured this was a pretty long incubation period.” But she never would have guessed this long, she said. “I mean, that many years of not eating? How on earth do they do that?”
Indeed, female octopods tend to be totally responsible for their egg clutch, and can’t leave it to hunt while the eggs are incubating. With most only producing one set of hatchlings, most of the female lifespan is dedicated to protecting the eggs, their own health slowly waning as the babies grow to independence. “It does make sense from an evolutionary standpoint,” Voight said, “because in the deep sea, food is even patchier, and babies are even more vulnerable.”
To ensure survival of her young, Voight said, a deep sea octopus might do well to invest even more time in her eggs than her shallow-sea counterparts. It’s possible that the low temperatures of the deep sea allow for a sort of hibernation, or that the octopods sometimes catch and eat the predators that wander too close to the eggs.
This lone deep-sea mama adds one more data point to the story, and Voight thinks the new study is building a case for longer living, longer brooding octopods in the deep. But if we knew more about the deep sea, we might not find such a long incubation period unusual. “It’s the biggest habitat that holds life on the planet, and we know the least about it,” Voight said.