Deep-sea squid go from transparent to dark as fast as a Kindle
Amazing, living e-ink displays of the ocean
US-based scientists have left the tech world flabbergasted today with the discovery that living e-ink displays – very bit as responsive as those found in a Kindle or similar e-reader – have been found swimming about deep beneath the Pacific Ocean.
As the vid above shows, the remarkable Japetella heathi, a bulbous, short-armed, 3-inch octopus, and Onychoteuthis banksii, a 5-inch squid, are normally quite transparent. But when a certain shade of blue light is shone upon them, they almost instantly turn dark.
The cephalopods' abilities are a defence mechanism, apparently arising from the fact that they operate on the depth boundary between two main kinds of deep-sea predators who might fancy them for lunch.
Many of the hungry enemies of J heathi and O banksii spot prey by seeing its silhouette against the light waters above, illuminated by the sky. To avoid these, staying transparent is best. Those parts of the cephalopods which can't be fully see-through – for instance their guts, filled with food – are reflective, as that's the next best thing.
Deeper down, however, many ocean hunters use bioluminescent lighting of their own to illuminate prey. The transparent condition, used against these, would be a bad idea as the predators would easily detect the cephalopods' reflective innards. Thus, when J heathi and O banksii notice that they are being illuminated strongly by certain wavelengths of light – blue is favoured by ocean creatures as it penetrates water better, as any diver will know - they swiftly turn themselves dark.
The cunning creatures apparently move to different depths as they age, and so adapt their active-sensing defence response, increasing the number of e-ink style chromatophores in their bodies.
"Smaller young animals are found higher in the water column and have fewer chromatophores, so they are more reliant on transparency, which makes sense because there won't be predators using searchlights there," says postdoctoral researcher Sarah Zylinski, one of the creatures' discoverers. Zylinski spent a good deal time at sea in the Pacific last year lighting up squid and octopi with different wavelengths in order to do so.
Swift as the remarkable seagoing display creatures are, it seems plain that they would be incapable of showing video at any appreciable frame rate. Perhaps, however, still speedier squid are yet to be found capable of colour and reasonable levels of animation.
Zylinski's paper Mesopelagic Cephalopods Switch between Transparency and Pigmentation to Optimize Camouflage in the Deep is published  in the journal Current Biology. ®