Hakai Magazine

Coastal science and societies

Hiding in Plain Light

A natural phenomenon of light and waves helps prey fish use stealth when running from predators.

Authored by

by Katrina Pyne and Amorina Kingdon

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It’s one of those things that everyone recognizes, but no one really knows the name for: the quivering light cast by sunlight through waves that makes a netlike pattern on the bottom of lakes, oceans, or swimming pools. The phenomenon is called water caustics, and it may help some fish on coral reefs escape predators.

Reefs are hotbeds of biodiversity, which means lots of species and lots of hunting. Naturally, prey fish have developed diverse strategies to flee, fight, or freeze when faced with predators, and, with their study of caustics, researchers may have found one more. The phenomenon seems to obscure prey fish from predators, delaying attacks and buying prey precious seconds to get away. Here’s how some reef fish might use these wavering lines of light for protection.