Bioluminescence is an amazing thing. Many living creatures use it to “light up” so they can communicate with others, more easily find food, or defend themselves against predators. In the picture above, for example, there are millions of single-celled organisms (called “dinoflagellates”) in the water. When they are disturbed, they use bioluminescence to glow. They are glowing in the picture because the wave is disturbing them. This is actually a defense mechanism. If the water is disturbed by an animal that eats them (such as a manta ray), the dinoflagellates glow, and the light might attract a predator that will eat (or scare away) the manta ray.
E. A. Widder wrote a review1 of bioluminescence in the May 7th issue of the Journal Science, and it is fascinating. As Widder points out, there are over 700 genera (the classification level above species) of organisms that use bioluminescence, and most of them (about 80%) live in the ocean. The mechanisms by which this process works are elegant and amazing, and they certainly defy any coherent evolutionary explanation.