The ability to produce light is widespread in marine organisms, but nowhere is it more
prominent than in the twilight regions of the midwater zone. In fact, at depths between
500 and 1,500 meters, it is more surprising to find an organism that is not
bioluminescent than one that is.
In the sea, luminescence occurs in everything from single-celled radiolarians and
bacteria to urochordates and fish. It has evolved independently many times, and this
convergence indicates that light-production must convey a strong selective advantage to a
variety of organisms.
Despite its widespread occurrence, many fundamental questions have not been completely