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Thursday, June 21, 2012

Octopus: master of disguise

As we saw yesterday, octopuses have an amazing ability to camouflage themselves. This is particularly remarkable when you consider that any predator the octopus would be hiding from would have a completely different vantage point. The octopus’s view of the sea floor  is entirely different from that of a fish hunting from above. If the target area is littered with many colors and textures, as in a coral reef, the octopus has to choose whether to mimic a specific item or to match the general appearance of the background. Noam Josef and Nadav Shashar of Ben-Gurion University of the Negev, and Piero Amodio and Graziano Fiorito of Stazione Zoologica Anton Dohm tested some octopuses to see which way they would blend.

The researchers used eleven images of Octopus cyanea and O. vulgaris, taken in the wild by SCUBA divers. Because of the way the sampling was done, the authors were confident that each image represented a different specimen. However, as the octopuses were not tagged (and were indistinguishable to human eyes), there is some chance that the same individual was photographed twice. For each picture, the appearance of the mantle (body of the octopus) was compared to that of the total background area and to specific objects within that field of view.

It turns out that octopuses mimic particular objects around them, and not the general appearance of a stretch of sea floor. In other words, an octopus will try to impersonate one rock rather than a rock-strewn field. This means that you can often see the octopus easily enough, you just didn’t realize that it was an octopus. If you watch yesterday’s video clip again, you can find examples of this.