Phosphorescence of the Sea

a phenomenon observed at night as a result of the bioluminescence of organisms in the surface layers of the sea. The luminescence of these organisms is stimulated by mechanical irritation, such as movement of the waters at current intersections, the action of waves or the wake of a ship, or the collisions of the organisms with each other, or it may arise as a reaction to a flash of light produced by nearby organisms.

Phosphorescence of the sea is observed everywhere, except in waters of very low salinity, and is especially frequent in certain tropical and temperate regions, for instance, the Gulf of Aden, the Bay of Biscay, and off the coasts of India and North Africa. The phenomenon may extend up to hundreds of square kilometers in area, or it may be seen as individual spots or bands. Distinctions are made between the milky phosphorescence produced mainly by bacteria, the flashing phosphorescence originating from accumulations of small planktons, such as per-idiniums and various crustaceans, and the pulsating phosphorescence produced by relatively large animals, such as jellyfish, ctenophores, and pyrosomes. The intensity of the light may reach 0.1–0.3 candela/m².

Phosphorescence of the sea is important in marine navigation, since it makes the shoreline and shoals visible; however, it may also create the false impression of shallow-water surf. In fishing, the phosphorescence helps in detecting concentrations of fish, and in naval operations it makes submarines, torpedoes, and ships visible.