Deep-Sea Crabs Use Color Vision to Search Food

Crabs living in deep sea waters use color vision to find their food, finds a new study.

A team of researchers led by Tamara Frank, a biologist at Nova Southeastern University, studied the effect of bioluminescence on the bottom-dwelling species to understand how the species use the light to interact with their environment.

They studied three ocean-bottom sites near the Bahamas by taking videos and images in order to find how crustaceans react to the bioluminescent light emitted by other deep sea mammals, according to a news release from the Duke Univeristy.

Some of the sea water species are known to be bioluminescent, which means that they emit light on their own. Lanternfish are bioluminescent, wherein they have luminous patches that emit a glow naturally. Such species use their bioluminescence in order to find their prey.

It also helps other deep-sea mammals to use this property to find their food. Earlier studies have shown that southern elephant seals, which spend more time in the deep-sea waters, are sensitive to blue light emitted by the lanternfish and use it to feed on them. They also use it as a means to communicate with other members of their species.

For their new study, Frank and her colleagues recorded videos and captured images of deep-sea mammals emitting bioluminescent light. They caught eight species of crustaceans and examined their eyes. They flashed different colors and different intensities of light in order to record the eye responses using electrodes. They found that all the species were sensitive to blue light, while two particular species alone were sensitive to both ultraviolet and blue lights.

Surprisingly, experts also found that the two species were using two different light-sensing channels to detect and respond to the light. While sunlight can penetrate the surface waters, the deep-sea waters are pitch dark with no light reaching the bottom. In an earlier study, it has also been shown that some species of the deep-sea waters can see UV wavelengths in lightless areas.

"I personally think it's fascinating that there are animals that see UV in one of the most UV-poor habitats on the planet," BBC quoted Prof Sonke Johnsen, one of the study authors from Duke University.

According to the researchers, crabs belonging to the crustaceans species are one such deep-sea mammals that see both the UV light and the blue light which helps to grab their food.

The study suggested that the crabs are likely color-coding their food using the UV and blue light. Experts are further planning to catch more crabs and study their sensitivity to shorter wavelengths of light.

The findings of the study are published in the Sept. 6 online edition of The Journal of Experimental Biology.