phosphorescence

phosphorescence, a faint blue-green light emitted from the sea at night, either as a continuous glow or a series of tiny flashes. This light is produced by the bioluminescence of living organisms ranging from bacteria to the many species of plankton, including phytoplankton, especially dinoflagellates. On moonless nights in late summer, flashes of light in the surf breaking on sandy beaches are often produced by the appropriately named dinoflagellate Noctiluca. Bioluminescence is produced by a chemical reaction and serves a wide range of functions. Deep in the ocean where there is little or no daylight, almost every species has some light-producing capability. The wavelength of the blue-green light emitted is the same as the residual daylight that penetrates to the greatest depths in the ocean. In a darkened environment signalling by light is an effective way of communicating with other animals of the same species, especially to confirm species identification during mating, or to indicate a readiness to mate. Lights are also used on lures to tempt prey within range. Bright flashes are used as a defence mechanism, startling the attacker. Glowing smoke screens or even phantom decoys are also used to avoid attack. In an environment where the brightest daylight comes from directly overhead, animals are particularly vulnerable to attack from below by predators that pick out their silhouettes. Lights arranged along the underside of fish and some Crustacea like prawns break up the silhouette, and act as a form of camouflage.

Some phosphorescent phenomena have a physical origin. During electrical storms structures like a ship's mast can become surrounded by a corona of electrical discharges giving an eerie bluish light called St Elmo's Fire.

Bibliography

Herring, P. , The Biology of the Deep Ocean (2002).

www.lifesci.ucsb.edu/~biolum/www.islandnet.com/~see/weather/elements/stelmo.htm

M. V. Angel