Some crabs on the sea floor can see UV light and use the
ability to select healthy food.
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."