Squid use polarization vision for survival

By Environmental News Network staff

Squids developed polarization vision to help detect plankton and other organisms whose transparent bodies might make them otherwise invisible.

Sport fishermen wear polarized sunglasses to enhance their vision of trout swimming in a stream and thus increase their chances of hooking the fish. Squid, researchers found, have long used polarization vision for their survival.

Squids are voracious predators who feed on a variety of marine organisms, including plankton. Plankton, in the co-evolutionary arms race for survival, have evolved a transparent body to protect themselves from predators, such as squid.

However, determined not to lose the arms race, squid, it turns out, have developed a visual system that enables them to see through this camouflage of transparency.

Scientists at the Marine Biological Laboratory in Woods Hole, Mass., conducted a series of experiments to determine the role that polarization vision plays in the life of squids.

It turns out that they developed polarization vision to help detect plankton and other organisms whose transparent bodies might make them otherwise invisible.

Polarization vision works by enhancing the contrast of transparent prey, thus making the invisible visible. The result is increased predation and feeding success by the squids, and perhaps even the assurance of long-term survival-at least until the no-longer invisible plankton evolve a more effective means of hiding from their savvy predators.

This enhancement in prey detection achieved by the squid is identical to that which the researchers achieved a few years ago while using an artificial camera designed for polarized light imaging. Hence squid have long ago developed a visual system that is equal or even better than current state-of-the-art imaging systems.

In addition to detecting prey, polarization vision seems to be used by squid, and other cephalopods, to display unique patterns that are invisible to some of their predators, as well as to humans. Decoding this potential secret language, and understanding other functions of polarization vision, is the focus of on-going research at the MBL's Marine Resources Center.

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