Animals in the lower mesopelagic zone (600–1,000 meters depth) of the oceans have converged on 2 major strategies for camouflage: transparency and red or black pigmentation. ~ American biologist Sarah Zielinski & Sönke Johnsen
Hiding in the ocean depths is not as easy as it might seem. Cephalopods illustrate the camouflage conundrum.
Some of their predators, like hatchet fish, hunt by diving deep and looking up for silhouettes of potential food. To avoid being seen, it helps to be transparent and so not cast a shadow.
Other predators, like deep-sea dragonfish, patrol using bioluminescent searchlights that reflect off clear flesh. In the presence of these glowing adversaries it’s safer to be as dark as the surrounding water.
The common clubhook squid and the Japetella octopus independently evolved a nifty solution to this dilemma: instantly switch disguise.
To alternate camouflage, the 2 cephalopods have distributed sacs of black pigment which they can twitch-switch. When it’s dark and the cephalopods want to be transparent, the sacs form compact spheres, letting the creatures’ glassy flesh show. When a light appears, the sacs flatten and stretch toward one another, shrouding the cephalopods in pigment.
In less than a second, it’s on and off. ~ Sarah Zielinski