Standing at the helm of the Santa Maria off the coast of Bermuda in 1492, Christopher Columbus was captivated by a faint light “like the light of a wax candle moving up and down” in the water. At first, he mistook it for a sign of land, but it wasn’t: It was the unexplained phenomenon that sailors knew as “the burning of the sea.” It had been known for centuries—Greek sailors attributed odd twinkles and eerie glows to the powers of the god Poseidon or one of his nymphs—but it wasn’t until the 18th century and the advent of microscopes that the true source was identified.

La Jolla, via Phillip Colla

Today, we know the phenomenon as tiny planktonic creatures that, when a wave or boat or swimmer disturbs them, twinkle blue, thanks to the same bioluminescent enzymes that give fireflies their glow. In the depths of the ocean, the only light available is the one these creatures create themselves; they use it to communicate, to find food, to find love, and to warn off predators. For us, it provides a stunning shoreside glimpse into the oddities of our oceans.

Alamy

Dinoflagellates are one of the most common bioluminescent organisms found in shallower water. They light up when a boat cuts through the ocean—in the past their light has exposed submarines and torpedoes. Bioluminescence almost never occurs in fresh water, but it’s such an important function for marine animals that live deep in the ocean that it’s evolved independently at least 40 times. Australia’s Gippsland Lakes aren’t always salty enough, but when enough seawater seeps in, the dinoflagellate Noctiluca scintillans thrives. These feed on phytoplankton; other bioluminescent bacteria consume rotting wood or dead fish, which, left long enough, can also start to glow blue. Bioluminescence can be visible on the beach in Vaadhoo, in the Maldives‚ but only when a passing ship disturbs the water.

Vaadhoo, via Corbis