Leather coral fluorescing underwater, photographed at night using blue coloured flashlight and a yellow filter. Blue light excites pigments within some underwater organisms such as this coral, causing them to emit a fluorescent glow. Corals harbour symbiotic algae which require light to photosynthesize and produce nutrients. It is thought that in shallower waters, the fluorescent pigments act as a sunscreen that prevents too much ultraviolet light damaging the algae. In deeper waters and lower light levels, it is thought that the fluorescent pigments absorb ultraviolet light and emit it at a wavelength which promotes photosynthesis in the symbiotic algae. Photographed in the Lembeh Strait, North Sulawesi, Indonesia.
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