During recent research into how cuttlefish adopt camouflage positions, a common cuttlefish (left) raises two of its eight arms in apparent mimicry of artificial algae placed in its tank. The animal reacted similarly when shown a photo of green algae, said biologist Roger Hanlon.
But the recent lab experiments are the first to confirm that cuttlefish use visual information to determine those gestures, according to Hanlon, of the Marine Biological Laboratory in Woods Hole, Massachusetts.
"Camouflage is one of the least studied subjects in biology. It would be nice if our paper encourages folks to look at this behavior more carefully in other animals," said Hanlon, whose new study was published May 11 in the journal Proceedings of the Royal Society B: Biological Sciences.
Shown in the wild, a Caribbean reef squid—a cuttlefish cousin—raises its arms straight up, parallel to soft coral branches.
Some shape-shifting cephalopods—squid, octopuses, and cuttlefish—can hold their positions for as long as 40 minutes, Hanlon said. "It's not a temporary thing, when they want to go in there and look like a piece of the swaying soft coral."
In the case of Caribbean reef squid, long dark stripes add to the disguise. "It's a very elegant and sophisticated pattern," said Hanlon, whose research has received funding from the National Geographic Society's Committee for Research and Exploration. (The Society owns National Geographic News.)
Photograph courtesy Roger Hanlon, Marine Biological Laboratory
Cuttlefish Falls in Line
A common cuttlefish lifts its arms upright (left) and at an angle to match stripes in an aquarium.
The use of two-dimensional patterns allowed the researchers to precisely measure how well the arm positions corresponded to the backdrops—and to rule out the possibility that the animals were basing their configurations on touch, according to study co-author Hanlon.
And because the experiments were done in controlled aquariums, the researchers could be sure the cuttlefish weren't reacting to chemical cues.
Reaching about 17 inches (45 centimeters) long, the common cuttlefish changes its color and skin texture to evade predators, including marine mammals, fish, and seabirds.
"They have an enormous variety of predators, some of which have marvelously good visual capabilities," Hanlon said. "That's why the [cuttlefish] camouflage has to be so good."
A wild common cuttlefish in Turkey points its arms into the sand, mirroring algae branches nearby.
Found along shorelines in most parts of the world, but not in the Americas, these cephalopods can assume camouflage positions within seconds of entering a new environment when they sense danger is near.