Videos featuring nighttime shores, where every footstep or water splash prompts a bright azure glow, resemble visuals from the movie “Avatar.” But this is an entirely earthly event—bioluminescence. We’ll explain why it happens and where one can witness it.
Most often, phytoplanktons, specifically dinoflagellates, are the cause of the spectacle. These are single-celled organisms whose bodies contain the substance luciferin. When it reacts with oxygen, an emission of cold light occurs.
The main query: why do they require this? After all, the luminescence makes them visible in the darkness. Scientists believe this is a clever defensive response, operating on the principle of an “alarm.”
When a small crustacean tries to consume plankton, the latter flashes. The vivid light in the dark frightens the predator. Furthermore, the flash functions as a beacon for larger fish: “Look, someone is feeding here, swim over!” Consequently, the large fish consumes the crustacean, and the plankton remains unharmed.
The illumination is activated precisely by mechanical impact. This is why the water shines when a wave breaks against it, when a boat maneuvers through it, or when you move your hand through it. The plankton perceives an assault and activates its defense.
Occasionally, larger creatures—like jellyfish or ctenophores—also illuminate. For deep-sea fish, light serves distinct purposes: luring prey—as with the anglerfish—or finding a mate in the gloom.
One can observe this marvel in numerous locations globally, from the Maldives to Crimea and Primorye, usually in late summer or early autumn when the water is warmest and plankton is rapidly multiplying.
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