Crabs living half-a-mile down in the ocean, beyond the reach of sunlight, have a sort of color vision combining sensitivity to blue and ultraviolet light. Their detection of shorter wavelengths may give the crabs a way to ensure they grab healthy grub, not poison. "Call it color-coding your food," said Duke biologist Sonke Johnsen. He explained that the animals might be using their ultraviolet and blue-light sensitivity to "sort out the likely toxic corals they're sitting on, which glow, or bioluminesce, blue-green and green, from the plankton they eat, which glow blue." The discovery explains what some deep-sea animals use their eyes for and how their sensitivity to light shapes their interactions with their environment.
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