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Why do dinoflagellates such as Noctiluca scintillans make seawater appear to glow?

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time-lapse photo of fireflies — Bioluminescence Time-lapse image of fireflies in the Catskill Mountains, New York. Firefly light is a cold light, with approximately 100 percent of the energy given off as light and only a minute amount as heat. Only light in the visible spectrum is emitted.

Dinoflagellates such as Noctiluca scintillans cause seawater to glow through a process called bioluminescence, which is a heatless light generated by a chemical reaction within the organism.1

This phenomenon occurs when a light-emitting pigment called luciferin is oxidized in the presence of an enzyme known as luciferase. In Noctiluca, these substances are contained within thousands of granules located in the organism's cytoplasmic strands.123

The glowing effect is typically triggered by mechanical stimulation, such as the agitation of water by waves or the movement of a swimmer. When the organism is disturbed, this chemical reaction produces a flash of blue-green light. Because this light falls near the point of maximum transmission for seawater, it is highly visible, creating the "sea sparkle" or "burning of the sea" effect often observed at night during population blooms.341