Many species of coral produce fluorescent pigments that light up in a dazzling display of neon colours when exposed to UV light.
Fluorescence is the phenomenon whereby a substance absorbs electromagnetic radiation (such as light) and emits it at a lower energy level. In this case, the corals’ fluorescent proteins absorb invisible high energy UV light and emits visible light, which has longer wavelengths and lower energy.
Scientists have hypothesised several reasons for fluorescence in corals.
Corals form symbiotic relationships with algae called zooxanthellae, which they house in their polyps. The algae photosynthesise and provide nutrients for the coral. However, the algae are not able to process UV light. Through fluorescence, the corals may be able to turn the UV light into wavelengths that are useful to the algae for photosynthesis, especially in darker environments.
It has also been suggested that the fluorescence provides protection against UV rays, notably in shallow water. UV rays are mutagenic and are capable of damaging cells in both the coral and symbiotic algae. Fluorescence may be a means to convert UV light into harmless lower energy wavelengths in order to protect both the coral and algal cells.
Studies have shown that corals with higher concentrations of fluorescent proteins are more resistant to bleaching.
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