What causes waves to sometimes flash a blue-green light at night?

Tiny single-celled Noctiluca can appear by the millions in the sea and produce a beautiful, greenish-blue light.

Tiny single-celled Noctiluca can appear by the millions in the sea and produce a beautiful, greenish-blue light.

November 2003

This occasional and beautiful phenomenon is caused by very small living organisms called Noctiluca. The flash is most often seen at night when waves crash onshore. When Noctiluca are in the water and ride the waves to shore, even your footprints will flash as you walk along the water’s edge.

The brief flashes of light are known as bioluminescence. Other marine animals also produce light, but blue-green flashing waves indicate a mass of Noctiluca producing tiny pinpoints of light. The small, single-celled organisms live by the millions in the sea.

Noctiluca is Latin for “night light.” The minute organisms belong to a group of microscopic plants known as dinoflagellates, a unique group that possesses characteristics of both plants and animals. Noctiluca produce light when disturbed or agitated. Disturbances can include billowing swells, waves, sea spray, boats, fish, dolphins and the like.

When incoming waves scatter Noctiluca on shore, small, burrowing shore animals, such as mole crabs and coquinas twinkle, as they become awash with the glowing organisms.

The mechanisms behind bioluminescence are not completely understood; however, scientists know that a chemical process takes place and the eerie light is a byproduct. Luciferin and luciferase are the chemicals involved.

Other marine animals that can also produce light include certain types of worms, comb jellies, several mollusks, squid, crustaceans and some fishes. The light of some fishes and squids is produced by bacteria living in their organs. Deep water animals may use the light-producing organs as a means of communication, a method of attracting food, a defense mechanism, a mating behavior or all of these.