How to survive in the dark: bioluminescence in the deep sea.

Bioluminescent tissues in marine organisms may take the form of point source emitters, internal or external glandular organs or glands containing bacterial symbionts. In many cases additional accessory optical structures have been evolved to increase the efficiency of emission, to restrict the angular direction, to focus or collimate the light, to alter its spectral distribution or to guide it from the source to a distant point of emission. This variety of structure is matched by a variety of locations of luminous tissues and organs over the body of different animals. The time course, intensity and spectral nature of bioluminescence are equally variable. Information can be encoded in the spatial pattern, time course and spectral characteristics of bioluminescent signals and the recognition of this information depends upon the visual abilities of the target organism. The known characteristics of the bioluminescence of certain marine organisms are compared with those that would be predicted for different functional interpretations. It is probable that each type of bioluminescent signal in deep-sea organisms is but one factor in the suite of activities which make up a particular behavioural pattern.