Quorum sensing on a global scale: massive numbers of bioluminescent bacteria make milky seas.

Many in the field would not have believed that luminous bacteria could be responsible for continuous and substantial light emission from the surface of the ocean extending over an area as large as the state of Connecticut and detectable from space. But in a recent paper in the Proceedings of the National Academy of Sciences, Steve Miller and colleagues report such a luminescence event detected by a satellite sensor system (25); this event persisted for three consecutive nights in the northwestern Indian Ocean near Somalia in 1995 (see cover), and they judged it to be due to light-emitting bacteria. How did the authors uncover this remarkable display? As Miller tells it, during a lunchtime chat with his colleagues Tom Lee and Carl Schueler at an American Meteorology Society Conference held in Seattle in 2003 the question was raised as to whether bioluminescence might be detected by satellite sensors. No one thought that the well-known and readily observed dinoflagellate emission would be detectable from space, but Miller kept wondering if there might be some other kind of bioluminescence that could be. On returning to his home base at the Naval Research Laboratory in Monterey, Calif., he searched the World Wide Web and found descriptions of so-called milky seas. Although this phenomenon is not often mentioned in the scientific literature (15, 27), there have been hundreds of strikingly similar reports by mariners over the last several hundred years of eerie displays dubbed milky seas consisting of continuous and widespread luminescence from the surface of the ocean, many of which are recorded in logs of merchant ships (19, 33). In searching these reports, Miller found a reference to a likely and ultimately fruitful milky sea sighting logged by the S.S. Lima, transiting an area on the night of 25 January 1995, which reported that, “At . . . (2200 local time) on a clear moonless night a whitish glow was observed on the horizon and, after 15 min of steaming, the ship was completely surrounded by a sea of milky-white color with a fairly uniform luminescence. The bioluminescence appeared to cover the entire sea area, from horizon to horizon . . . and it appeared as though the ship was sailing over a field of snow or gliding over the clouds.. The bow waves and the wake appeared blackish in color . . .” The Internet also led him to the bioluminescence web page of the University of California, Santa Barbara, and ultimately to Steve Haddock, a specialist in bioluminescence at the nearby Monterey Bay Aquarium Research Institute in Moss Landing. They enlisted the help of Chris Elvidge of the National Geophysical Data Center in Boulder, CO, to retrieve archival data acquired at that time from the U.S. Defense Meteorological Satellite Program constellation of satellites. Miller and Haddock independently saw a faint feature in the raw data in the vicinity of the area described in the ship report. When they enhanced the imagery in that area and overlaid the ship coordinates, there was a eureka moment. The agreement with the coordinates of the S.S. Lima was exact! Icing on the cake came when Miller discovered that milky seas were described in a discussion between two crew members in Jules Verne’s classic Twenty Thousand Leagues under the Sea at a level which indicated that Verne used actual ship logs for some of his raw material. Curiously, the “milk sea” described by Verne (32) occurred on the same day of January as the third night of the satellite imaging.