Fluorescent coral. Large-polyped Stony coral, Euphyllia paraglabrescens. Above photographed with daylight and bellow showing fluorescent colours photographed under special blue or ultraviolet light and filter. Many corals are intensely fluorescent under certain light wavelengths. Shallow water reef-building fluorescent corals seem to be more resistant to coral bleaching than other corals, and the higher the density of fluorescent pigments, the more likely to resist. This enables them to better protect the zooxanthellae that help sustain them. The pigments that fluoresce are photoproteins, and a current theory is that this acts as a type of sunscreen that prevents too much UV light damaging the zooxanthallae. These corals have the photoproteins above the zooxanthallae to protect them. Corals that grow in deeper water, where light is scarce, are using fluorescence to absorb UV light and reflect it back to the zooxanthallae to give them more light to turn into nutrients. These corals have the photoproteins below the zooxanthallae to reflect it back. Photographed in aquarium. Portugal