More common in water than on land, bioluminescence has evolved multiple times in the ocean. Marine animals make use of a variety of light-emitting systems—from luminescence to fluorescence—that allow them to occupy different habitats and levels within the water column.
The Shimmering Surface: Step into a sheltered Caribbean bay on a dark night, and watch the water’s surface sparkle and glitter. Millions of tiny marine plankton called dinoflagellates flash on contact, creating a glowing halo around anything that moves through the waves.
Why the spectacular lightshow? Scientists theorize that the sudden flash both startles and exposes attacking predators and may cause a chemical reaction that acts as an antioxidant by removing toxic oxygen radicals.
Riveting Reefs: Along dark reefs below the surface of the Caribbean Sea, certain corals and sea anemones fluoresce in brilliant colors as if lit from within—but only when hit by certain wavelengths of light.
We can’t detect this 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. Fluorescent molecules may also also serve as sunscreen, protecting corals by filtering out harmful ultraviolet rays.