A white octopus sat on the seabed, gently waving its short, stubby arms and staring with piercing eyes at the camera of a deep-diving robot.
That was in 2016, in the waters off Hawaii, at a depth of 4,290 meters (2.6 miles). No one had ever seen an octopus quite like this, and certainly not so deep. Due to his ghostly appearance, he was nicknamed Casper.
Until then, the only cephalopods filmed at such depths were the Dumbo octopuses, named after another cartoon character, seen swimming up to 6,957 meters, with elegant ear flaps on each side of the head.
Casper’s sighting was a defining moment for Janet Voight, associate curator of invertebrate zoology at the Field Museum of Natural History in Chicago. “It’s totally new and different,” she says, recalling the discovery.
This first glimpse of Casper raised many tantalizing mysteries. Why is he so pale? Most other octopuses have colored chromatophores in their skin that change appearance in an instant and act as camouflage to confuse predators.
Even on the high seas, octopuses can be colored, such as purple, warty Graneledone. Some use a cloak of dark skin pigments, apparently to hide glowing, bioluminescent prey that they grab in their arms and thus avoid alerting other predators. Voight speculates that Casper’s paleness may come down to a lack of pigment in his food.
Another conundrum involves short arms, though Casper isn’t the only one with limited reach. “The more superficial and tropical you are, the longer and thinner your arms are,” says Voight.
This tendency to shorter arms in deep octopuses has no precise explanation. Voight thinks that, rather than stretching to grab food, they have developed an alternative tactic of twisting their bodies so that their mouths, below their bodies, are directly above their food.
Scientists learned more about Casper by sifting through five years of archival footage collected during deep-sea surveys across the Pacific. They spotted dozens more like Casper perched on the seabed, from two separate species.
“They might be quite common,” says Voight. “It’s just an indicator of how little we know about what’s out there.”
For Voight, the Caspers were particularly exciting with their arms wrapped around clutches of eggs stuck to large sponges. Previously, she had hypothesized that seabed octopuses needed hard rocks to lay their eggs. Lower down, there might be less exposed rock, which would limit their depth.
“Casper showed there were ways around it by finding a sponge rod,” she says. “Is this a breakthrough in the evolution of the octopus?”
The sponges themselves are attached to rock nodules scattered over stretches of abyssal plains and take millions of years to form.
If other deep-sea octopuses are to follow, female Caspers probably spend a lot of time guarding their eggs. An octopus of another species (Graneledone boreopafica) was seen off California, on a steep escarpment in the Monterey Canyon, brooding its single brood in exactly the same spot for more than four years.
As of now, Casper’s pale and mysterious octopuses don’t yet have an official name, because everything we know about them comes from imagery; no one has been able to collect a specimen to study in detail.
“With an octopus, you really need it in your hand,” says Voight.
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