Deep-sea Camouflage Tactics Revealed 61
Honken writes "A recent study by scientists at Duke University has found that transparent deep-sea octopuses turn red when exposed to blue light similar to what predators emit, allowing them to hide using both transparency and by absorbing the wavelengths of the blueish light emitted by deep-sea predators. The Register quickly made the not-so-obvious connection to Kindles and squid video playback, whereas Discovery News reports on slightly more useful yet exotic applications, such as fishing nets that are invisible only to the species that it intends to catch."
Squid are doing it for themselves (Score:5, Informative)
These two species aren't the only squid or octopuses (or cuttlefish for that matter) that have amazing abilities in their skin.
The Caribbean Reef Squid is able to flicker it's chromatophores and photophores on and off at greater than 120Hz, meaning that the squid are able to replicate the patterns of light and shadow against the sand and rock substrate caused by the waves in the water. It wasn't until we had some footage from The Discovery Channel taken with an HD high speed camera in an underwater housing that we realized that our original estimation of 30Hz for squid skin color change was way off. What we were seeing was the pattern as interpreted by our brain's somewhat limited image processing abilities.
This really didn't come as a surprise as squid have optic lobes in their brains that dominate all other parts, and their optic nerves are absolutely massive, easily 100 times larger than the comparable neurons in mammals.
Shallower and warmer water species of squid, octopus, and cuttlefish also have an ability that was touched on in the article, which is counter-shading their undersides to break up any silhouette they would create when seen from below. This is accomplished by photophores that emit light in similar frequency ranges as the sun after it passes through a few feet of water.
Squid also use their skin's full-motion video ability for mating displays and communication, but I think I've already babbled on about squids enough.
Re:Squid are doing it for themselves (Score:5, Informative)
It depends on what you're asking.
Their camo is for defensive purposes only.* They get off kind of light as far as skin goes. They use kinesthetics to fool predators but tend to remain in a default black and white coloration. Most fish, and I would guess that enough animals that are predators of the mimic are color-blind. Most octopuses and squid are as well. Instead of color vision though their eyes filter the different polarizations of light and the guess is that they process the difference in polarization the same way we'd process a difference in color. So, instead of matching a background color, a mimic gets away with matching a background tone and then altering its body postures to produce a convincing enough silhouette.
The black and dark colors are made by chromatophores, the white is make by leukophores.
One interesting and thoroughly unscientific experiment I did involved altering the polarization of light my eyes were receiving, and then looking at squid and their predators while diving. I got a pair of welding goggles with replaceable lenses then ordered some circles of polarized glass. I got two lenses that only allowed vertical or horizontal light (depending on the angle of the channels to your eye) and glued them in to the goggles with some reference marks.
With both lenses vertical I saw a lot of amazing stuff. The scales on fish were a lot less fuzzy and I could make out parts of the squid displays with more clarity. With both lenses horizontal, the scales on fish that normally looked silver would appear black at some angles. When I did one lens H and one lens V, I got a massive headache but my ability to pick out the details of fish and animal movement was increased by quite a bit. At the same time, the squid and the displays on their skin were brought in to sharp focus in some directions and very very confusing waviness in others.
There was much mind blowing and Advil taking that day. However, that was exceptionally unscientific of me, and is presented as "hey, isn't that cool" only.
*that we've observed in the wild. To my knowledge, no one has had observed mimic octopuses mating.
Re:Squid are doing it for themselves (Score:5, Informative)
I still eat squid, but I can't eat octopus for the reason you cite.
I eat squid because everything eats squid, including other squid. Most of the calamari you get in restaurants is either California Market Squid or one of the more common species of Loligo, (which just had a taxonomy change and I can't remember the new genus) and they are, to use a scientific term, dumb as posts.
That's how I rationalize it anyway.
Re:Squid are doing it for themselves (Score:4, Informative)
YES! Finally! The one thing I can actually post intelligently about!
Feels good man.