Study Finds Deep-sea Crabs Locate Food With Ultraviolet Vision

Posted on September 6, 2012

Researchers have discovered that some deep-sea crabs use ultraviolet vision to find food. The Nova Southeastern University research study found that the crabs have eyes sensitive to ultraviolet light, which they can use to find plankton, grab it with their claws and stuff it into their mouths.

Tamara Frank, Ph.D., a marine biologist and associate professor at Nova Southeastern University's Oceanographic Center, and principal investigator of the study, said crabs living in the deep-sea zone may be using bioluminescence to help find their food. This region of the sea is pitch dark.

Study collaborator Sonke Johnsen, Ph.D., Duke University, says the crabs may use their vision sensitivity to distinguish plankton from the corals they are sitting on. The researchers say this coral is probably toxic. The toxic corals glow blue-green and green, while the plankton the crabs eat glows blue.

Johnson said in the announcement, "Call it color-coding your food." Johnson says these crabs 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 scientists studied deep-sea crabs found at sites near the Bahamas. They flashed different colors and intensities of light at the crabs and studied their reactions. The researchers found that all the deep-sea crab species are very sensitive to blue light and two species are very sensitive to both blue light and ultraviolet light. The researchers also used a special digital camera to capture true-color images of the bioluminescence of the coral and plankton at these same sites and found the coral glows a greenish color and the plankton glows blue. The researchers say their idea is still at the hypothesis stage.

The research was published here in the Journal of Experimental Biology.

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