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What is the "milky sea" phenomenon?

Behind the Milky Sea Mystery

After they determined the milky sea wasn't merely a creation of sailors with overactive imaginations, scientists' task was to figure out what was causing it. They had help in the form of water samples collected from the western Arabian Sea in 1985 during a three-day milky sea event. These samples indicated the presence of a type of bioluminescent bacteria in the water, known as Vibrio harveyi.

Luminous bacteria differ from the more commonly known bioluminescent dinoflagellates, which are responsible for the glow occasionally produced in ships' wakes or in waves crashing on the shore during a red tide bloom. Dinoflagellates emit short flashes of light, while bioluminescent bacteria produce a faint, sustained glow. The bacteria use two substances in a chemical reaction to produce light -- a luciferin, or light-producing substance, and a luciferase. This second substance is an enzyme that catalyzes the oxidation of the luciferin, creating light as a byproduct [source: Miller].

Unlike dinoflagellates, which commonly use their bright light to ward off predators, bioluminescent bacteria may actually use light to attract fish. They want to be ingested because their favorite place to live is inside a fish's gut. Since these tiny bacteria only emit a very faint light on their own, they have to gather together to make much of an impact. Their collective glow can grow to massive, milky sea proportions when their numbers swell to a huge amount -- think 40 billion trillion [source: ScienceDaily].

Dr. Miller and his colleagues haven't determined exactly what causes the bacteria to gather in such enormous numbers, but he hypothesizes that the bacteria may congregate to colonize organic material in the water. In the case of the 1985 samples of Vibrio harveyi, scientists found the bacteria colonizing the brown/green algae Phaeocystis.

Now, with the aid of satellite systems such as the DMSP, scientists plan to continue their study of the milky sea phenomenon. They hope to get more definitive answers about the science behind this strange and ethereal sight.