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Fluorescent Corals

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Fluorescent coral images - stock photos & facts showing the amazing colors that coral displays in blacklight

Corals are marine invertebrates of the class Anthozoa. They are small polyps that excrete calcium carbonate to form a hard “skeleton”, and most typically clump together to form reefs. A coral head may contain as many as several thousand individual polyps. Corals obtain most of their nutrients from algae called zooxanthellae that live within the polyp. Zooxanthallae use photosynthesis to produce food from sunlight.

Many corals are intensely fluorescent under certain light wavelengths. Why some corals fluoresce is not fully known and is a subject of much study. In particular, shallow water reef-building corals that fluoresce seem to be more resistant to coral bleaching than other corals, and the higher the density of flurorescent 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.

Corals show an amazing diversity of colors most of which are visible in daylight, but the fluorescent colors are only visible with black light in the dark. The corals fluoresce all the time, but sunlight is so bright that it is not possible to see the fluorescence. Corals are suffering from coral bleaching due to global warming, and fluorescence may be important in reducing the bleaching.

Corals get most of their nutrients from zooxanthallae, which are a symbiotic algae living within the coral polyp. However they can also catch plankton using the stinging cells on their tentacles. Corals breed by spawning releasing gametes simultaneously over a period of several nights, usually around the time of a full moon.
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