Unlike fireflies, glowworms, and other bioluminescent creatures, these brilliant corals don’t glow on their own. Instead, they absorb one color of light, and emit light of another color—a process known as fluorescence.
Fluorescent objects absorb light at certain wavelengths, then re-emit it. In the process, some energy is lost as heat. So the outgoing light has less energy—and a longer wavelength—than the light coming in. The change in wavelength means a change in color.
Fluorescent compounds may help corals survive, but the role they play is not yet well understood. Researchers are still studying these animals to find out more, but have suggested a few intriguing possibilities:
- Fluorescent molecules may serve as a sunscreen, protecting corals and the dinoflagellates that live inside them by filtering out harmful ultraviolet rays.
- Injured corals often form colorful patches. These colorful spots are also areas where the coral is making fluorescent molecules that act as antioxidants, capturing toxic oxygen radicals that threaten to damage cells.
- Corals glow by absorbing and re-emitting light from the Sun. We can’t detect their fluorescence in bright sunlight, but it’s possible that some animals can. Many corals glow around the mouth and tentacles, and might use their light to attract prey.
This mural—presented as a life-sized, interactive exhibit in Creatures of Light—captures a slice of life on Bloody Bay Wall, off Little Cayman Island in the Caribbean Sea.
In daylight, creatures on this coral wall can be seen in fine detail. The same areas look very different at night, when lit by high-energy spotlights.
The brilliant patches of red, green and orange come from corals, fishes and sea anemones. These vivid colors come from fluorescence, not bioluminescence. They only appear when the animals are illuminated by specific wavelengths of light.