June 1, 2012 | 2
The octopus is an amazing master of disguise. It can essentially vanish, right before your eyes, into a complex scene of colorful coral or a clump of kelp waving in the currents.
For a view of this phenomenon in reverse, check out this now-viral video shot by Woods Hole Marine Biology Laboratory senior scientist Roger Hanlon. The clip reveals how entirely the octopus was camouflaged before it was startled into jetting away—to the inevitable oohs and ahhs of the audience.
How do these invertebrates manage this quick-change feat? Small pigment-filled cells, called chromatophores, and reflective ones called iridophores and leucophores, in the skin of most octopuses allow them to create nuanced patterns of color, luminosity and even harness polarized light to fool other ocean life. But the information they use to craft the overall effect has been debated. Do they survey the whole area in their proximity and incorporate the general hues and patterns into their skin display, or do they pick out just a few nearby landmarks for a more precise match?
A new paper, published online last month in PLoS ONE, suggests that octopuses do focus on a limited selection of nearby objects in order to determine their disguise.
The researchers studied digital underwater photos of the common octopus (Octopus vulgaris) and the day octopus (Octopus cyanea) camouflaging in their natural habitats. They then ran those images through a software program that uses algorithms to pick out clusters of similar colors, lights and patterns. The almost-invisible octopuses in the images most closely “matched distinct landmarks such as corals, noticeable rocks, patches of unevenly colored sand, or an algae patch whose appearance different from that of its surroundings,” rather than the larger field of view, the researchers wrote.
“By reproducing key features of well-chosen objects, the octopus can produce an effective camouflage that may fool a wide range of potential predators,” Noam Josef, of Ben-Gurion University in Israel and co-author of the study, said in a prepared statement. This “point of view predicament,” as Josef and his colleagues describe it, is especially important in the ocean, where a predator could be a far-away finfish swimming in the water column or a lurking nearby eel—and potential prey could be skittering right by on the rock an inch away. So if an animal looks more like a specific object to animals both near and far, it is more likely to escape notice than if it averages out the appearance of an entire area.
The new paper does not, however, solve the debate about how these color-blind animals can create such a stunning, full-color display on their skins. The discovery of light-sensing cells (opsins) in their skin suggests that they might be able to detect and react to local color and light conditions locally. But so far, only one hue of these cells has been discovered, so scientists are still searching for more clues about how these crazy cephalopods pick their wild disguises.
Illustration courtesy of Ivan Phillipsen