Octopi: The New Kings of Disguise
by Ed Yong
Photo by Michael Nolan / SplashdownDirect / Rex USA.
At the age of 21, snorkeling the clear, blue waters off Panama’s coast, Roger Hanlon caught his first glimpse of it. As he scanned for vibrant sea life, his tall frame cast a shadow on an octopus below. Sensing danger, the creature blasted water at Hanlon before dashing off, its skin changing colors as it moved. First terrified, then intrigued, Hanlon chased the 1-pound mollusk for the next 20 minutes. “I just marveled at its changeable camouflage,” he says. “It moved along, fully exposed but really hard to see.”
Since then, Hanlon has spent more than 30 years tracking and filming thousands of octopuses, squid, and cuttlefish—collectively known as cephalopods—as they change the pattern, color, and even texture of their skin in waters around the globe. A senior researcher at the Marine Biological Laboratory in Woods Hole, Mass., Hanlon knows cephalopods’ tricks better than anyone else in the world. And now, he’s on the cusp of unlocking the secret of their chameleon-like talents.
Armed with a $6 million grant from the U.S. Office of Naval Research, Hanlon and a team of engineers are building technology that will duplicate the cephalopods’ spectacular abilities. What could humans do with such talent? Imagine pattern-shifting clothes or cars that regulate their temperature by changing color. Thanks to Hanlon’s work, that’s just around the corner.
The New Chameleons
As disappearing acts go, cephalopods are unparalleled. Instead of settling for one mode of camouflage, they’ve mastered just about all of them. This is in part because they live in the planet’s most visually diverse environments—coral reefs and kelp forests—where patterns of light and color vary more than even in tropical rainforests. But Hanlon suspects that their abilities evolved not because they have so much to hide against but because there’s so much to hide from.
“Cephalopods, being soft-bodied and nutritious, occupy that point in the food web that’s right in the middle,” says Hanlon. The creatures find themselves on the menu of virtually every ocean predator: birds, fish, dolphins, and plenty of others. And each of these predators has different visual powers. Some see ultraviolet light. Others detect polarized light. Still others have flawless nighttime vision. Cephalopods effectively have to hide from the most sophisticated eyes in the world. “We’re not looking at something humdrum that works against one or two predators in one or two habitats,” says Hanlon. Instead, cephalopods are wielders of über-camouflage: an omni-disguise that’s evolved to fool every possible prying eye.
Speed also matters. In just over two seconds, an octopus can completely transform from the stony, rugged hues of a rock to a smooth, ghostly white. But how does it access such a wide palette? The trick is in the skin: An octopus can expand and contract sacs of red and yellow pigments called chromatophores, which are dotted across its body but have uninterrupted nerve connections to its brain. Upon receiving a signal from those nerves, radial muscles pull outward on a sac, stretching from an inconspicuous speck to a flat, colorful disc. Meanwhile, underlying cells called iridophores have the ability to reflect cooler blues and greens from ambient light. Between these layers, the animals have the entire spectrum covered.
But camouflage for a cephalopod is about more than just a color scheme—the creatures can change shape too. Cuttlefish splay and ruche their arms, protruding small studs from their skin, until they resemble floating algae. Some octopuses transform themselves into rolling rocks or coconuts by walking on two arms while wrapping the others around themselves. And the most talented charlatan of them all, the mimic octopus, seems to imitate an entire toxic menagerie. Pulling its arms back into a flat leaf, it suddenly resembles a flounder. By hiding six arms and its head in a burrow, it passes for a sea snake.
The cephalopods are so good at hiding that Hanlon’s first challenge is finding them. Throughout the years, he’s perfected the art. He tracks some species by looking for the graveyards of their prey. “Octopuses are litterbugs,” he says. “They’ll gather crabs and clams and leave the shells around.” Once he’s marked a den, Hanlon will pull an early shift, staking out the territory until the owner comes back. “It’s very labor-intensive. I’ve gone through a lot of volunteer divers who spend their morning watching a stupid rock.”
Yet for Hanlon, the work is gratifying. He knows cephalopods could be the key to understanding camouflage in all species. And the creatures themselves still dazzle him. “They’re charismatic, interesting, and colorful, and they do things we don’t expect. That’s fun science.”
Finding a Pattern
Back in the lab, Hanlon and his team have placed cuttlefish on checkerboards, sand beds, and other surfaces of different patterns and colors, conducting plenty of analysis along the way. But of all the cephalopods’ abilities, Hanlon thinks that replicating background is the most important. While many visual predators have poor color vision, almost all of them are good at detecting mismatched patterns.
And for all the astonishingly varied backgrounds that cephalopods can mimic, Hanlon believes that their disguises come in just a few basic types. In 1998, he accumulated hundreds of cuttlefish photos and started sorting them into piles based on pattern. “Much to my surprise, I came up with just a few piles,” he says. More than a decade, thousands of photos, and several quantitative measurements later, “the same three pattern templates hold,” he says. In uniform mode, the animal’s entire body takes on the same uniform brightness, like a sandy floor. In mottled mode, the body displays small repetitive patches of light and dark, like a gravel bed. And in disruptive mode, it has bigger patches that sharply contrast with each other, presented in different scales, shapes, and orientations. This variation helps to break up the animal’s recognizable outline. Of course, there are plenty of minor differences, but it’s the low total number of patterns that intrigues him. “I don’t care if it’s two or 10, but I’m sure it’s not 55 or 1,000. That’s already a counterintuitive notion.”
Hanlon’s three-pattern hypothesis also explains how cephalopods can disappear from view within tenths of a second without needing “a brain the size of a Volkswagen,” since the animals can simply rely on one rule for each pattern type. For example, Hanlon’s team has shown that a cuttlefish will don its disruptive suit if it sees a light patch that’s sharply contrasted to the darkness around it. Rather than parsing through all the visual information surrounding it, the cuttlefish susses out a few key clues to determine the dress code.
But perhaps the strangest thing about their ability is that, while cephalopods can mimic the entire spectrum of colors, they themselves are color-blind. In 2008, Hanlon, along with fellow researchers Lydia Mathger and Steven Roberts, found a big clue: light-sensitive pigments called opsins dotted all over the creatures’ skin. Opsins are typically found in eyes and are essential for vision. The discovery raises the tantalizing possibility that these animals could sense light in a novel way. “Maybe there’s sensing going on in the skin, independently of the central nervous system,” says Hanlon.
As Hanlon probes these skin pigments further, his collaborators will take the biological principles and give them an engineering spin. Their plan is to develop materials that can sense light and change color with the same speed and efficiency as a living cephalopod—by using distributed light sensors that can coordinate brightness and color without needing a central “brain,” or processing unit. Understanding how the living animals do it will be critical. “The engineers are invariably astounded by the weirdness of it all, but once they get some numbers, they’re impressed by how efficient [the ability] is,” Hanlon says.
The potential applications are as diverse as they are exciting. “Think about townships with water towers or industrial plants with chemicals in holding tanks,” says Hanlon. “When they heat up or become too cold, they become a problem.” A light-sensitive coating that could change color to control how much heat it absorbs would solve that problem. Our favorite gizmos could benefit too. A squid’s skin is just as vibrant and dynamic as an iPhone but runs on far less energy. “If we work out how biological systems handle light and add that to our technology,” says Hanlon, “the efficiency’s going to go right up.”