Why does the ocean glow at night?

A nighttime cruise in the ocean can be a magical experience. Sometimes, sparkling lights in the water seem to outshine the stars in the sky.

The ocean itself doesn’t actually glow, but plenty of things that live in it do. The light they emit is called bioluminescence, and there are hundreds of different kinds of organisms on Earth that create it. Most of them live in the sea.

One kind of bioluminescence that many people are familiar with appears as sparkling streaks of light at the bow and in the wake of a moving boat in the ocean at night. The light comes from tiny, single-celled algae called dinoflagellates that live in seawater.

Water agitation prompts the light-giving chemical reaction in the dinoflagellates. Most light comes off as bluish, but different chemicals produce different colors. In the case of dinoflagellates, the intensity of light depends on the concentration of algae in the water. In some places, like the Indian Ocean, sailors have reported a soft white glow on the surface of the water — a “milky sea” that stretches as far as they can see.

Other types of bioluminescent organisms include fireflies, centipedes, fungi, squid, jellyfish, worms, and some fish.

For more information:

Bioluminescence web page (Univerity of California Santa Barbara)

Harbor Branch Oceanographic Institute’s bioluminescence page

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