Haha, this is really cool.
We all know how great cephalopods are at camouflage. An octopus can meld seamlessly into just about any realistic environment. Deep-sea squid are known to change the colour of the light they emit to match the colour of their surroundings.
Now here are a couple of cephalopods that switch from transparent to coloured and back in the blink of an eye. According to Zylinski and Johnsen (2011), this allows them to sort of have the cake and eat it in the very special habitat they share: the “twilight zone” of the ocean.
Twilight zone creatures, you see, face a dilemma. This is the depth at which some light from above may penetrate depending on the circumstances, but many organisms make their own light to hunt and communicate. The best way to stay hidden from the (mainly blue) headlights of deep-sea predators is to be red or black – but being dark means that the faint light from above exposes your silhouette to predators below you.
And the best way not to have a silhouette – i.e. letting ambient light through you – makes you positively shine in a strong, directed beam of blue light. No transparent animal is completely transparent, and much of the light you shine on them bounces straight back at the source – which is likely to be out for a nice juicy meal of octopus.
This challenge is a piece of cake for masters of camouflage like cephalopods, apparently. When simply swimming around in ambient light, the octopus Japetella heathi and the squid Onychoteuthis banksii are mostly transparent. Shine blue light on them, though, and they are covered in reddish spots faster than you can say “red” (red light and a variety of other stimuli don’t cause such a response). Just to be sure, the researchers also measured the animals’ reflectance – and sure enough, the dark versions reflected much less blue light than the “transparent” ones. The trick seems to work.
Like all cephalopod camouflage tricks, this one looks damned impressive. I don’t know if the videos uploaded with the article can be accessed without subscription, but if they can, they are well worth a look!
Also, Japetella is absolutely adorable 😀
Reference and image source:
Zylinski S and Johnsen S (2011) Mesopelagic cephalopods switch between transparency and pigmentation to optimize camouflage in the deep. Current Biology, in press