A white octopus sat on the sea floor, gently waving its short, stubby arms and peering with beady eyes into the camera of a deep-diving robot.
It was 2016 in the waters off Hawaii, at a depth of 4,290 meters (2.6 miles). No one had ever seen an octopus like this, and certainly not one this deep. Based on his ghostly appearance, he was nicknamed Casper.
Until then, the only cephalopods photographed at such a depth were Dumbo octopuses, named after another cartoon character seen swimming at a depth of 6,957 meters, with elegant ear-like flaps on either side of their heads.
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Seeing Casper was a startling moment for Janet Voight, associate curator of invertebrate zoology at the Field Museum of Natural History in Chicago. “It’s completely new and different,” she says, recalling the discovery.
This first glimpse of Casper gave rise to many harrowing mysteries. Why is he so pale? Most other octopuses have colored chromatophores in their skin that change their appearance in an instant and act as camouflage to confuse predators.
Is this a breakthrough in octopus evolution? Janet Voight, Octopus Expert
Even in the deep sea, octopuses can be colorful, like the purple warty graneledon. Some use a cloak of dark skin pigments, ostensibly to hide glowing, bioluminescent prey they grasp in their hands and thus avoid alerting other predators. Voight suggests that Casper’s paleness may be due to the lack of pigments in his food.
Another conundrum is the short arms, although Casper is not alone in his limited reach. “The shallower and more tropical you are, the longer and thinner your arms,” says Voight.
This trend toward shorter arms in deep-dwelling octopuses has no definite explanation. Voight thinks that instead of reaching out to grab food, they evolved an alternative tactic of curling their bodies so that their mouths, on the underside of their bodies, are directly over the food.
Scientists have learned more about Casper by combing through five years of archived footage collected during deep-sea surveys in the Pacific Ocean. They spotted dozens more of Casper’s lookalikes perched on the sea floor, of two different species.
Unusually, Caspers seem to lay their eggs on tall mushrooms rather than rocks. Photo: MBARI (Monterey Bay Aquarium Research Institute)
“They may be quite common,” says Voight. “It’s just an indication of how little we know about what’s down there.”
For Voight, Caspers with his hands wrapped around piles of eggs stuck to tall mushrooms were particularly exciting. She previously theorized that seafloor-dwelling octopuses needed hard rocks to lay their eggs on. There may be less exposed rock further down, limiting how deep they can go.
“Casper showed that there are ways to do this by finding a mushroom stalk,” she says. “Is this a breakthrough in octopus evolution?”
The mushrooms themselves are attached to rocky nodules that lie scattered across stretches of abysmal plains and take millions of years to form.
If other deep-sea octopuses are anything to go by, female Caspers probably spend a long time guarding their eggs. Another species of octopus (Graneledone boreopacifica) was seen off the coast of California, on a steep slope in Monterey Canyon, brooding its single clutch in the same spot for over four years.
So far, the pale and mysterious Casper octopuses have yet to be officially named because everything we know about them comes from images; no one has been able to collect a specimen to examine in detail.
“With an octopus, you really need it in your hand,” says Voight.
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