Why do so many marine animals have bright fluorescent pigments?
Fluorescence is a process where high-energy light temporarily excites electrons in a molecule. When the molecule relaxes, the energy is re-emitted as a lower-energy photon with a longer wavelength. For example, blue or violet light is often used to excite green, yellow, or red fluorescent emission. Fluorescence is a passive physical property of many molecules, and unlike bioluminescence, it is not something that animals can actively turn on and off.
To test how animals might use fluorescence we conducted predator-prey experiments with the flower-hat jellyfish. We found that the fluorescent tentacle tips, when excited by ambient blue light from the environment, were an irresistible attractant to potential prey. We also found evidence for fluorescent structures in a range of other predators.
For this video, we filmed the fluorescence of animals by shining a blue light on them and putting a yellow filter in front of the lens. The filter blocks out the excitation light but lets the fluorescent light be recorded. You can try it at home with a piece of yellow plastic and a blue LED flashlight. You might be surprised by what you find!
