According to researchers, Tamara Frank and Sönke Johnsen of Nova Southeastern and Duke universities, some Bahamian crab species would be able to distinguish blue, green and ultraviolet. In the great depths, the plankton produces, during a contact, a small light, it is the bioluminescence. Some emit a blue glow, others blue-green. Corals, for their part, diffuse a green halo.
Crabs, light and depth
These crabs live in the dark, at a depth of 800 meters. This ability allows them to distinguish the bioluminescence of the plankton they eat and thus differentiate it from the coral, sometimes toxic, on which they are living.
To identify the colors that the crustaceans could see, the researchers placed micro-electrodes on their eyes. Then they projected colorful flashes. All species of crab strongly reacted to blue, and 2 of them were also susceptible to ultraviolet.