The function of bioluminescence has been investigation for many years. Its abundance in the marine environment and the number of organisms that have retained functional eyes in an environment usually devoid of natural light, suggests that it is of high importance (Widder 1999).
Whilst its importance is easy to deduce, its behavioural functions are much harder to identify due to the requirement of constant observation. To many of us, the conditions which organisms in the deep-sea (>200m (Gage & Tyler 1991)) face would seem very extreme with low light, little food and low temperatures. However, to the organisms that live in these conditions this is normal and they are adapted to cope with life in this environment. Such conditions make observing specimens in situ for any significant period of time impossible. Expeditions can be made to considerable depths in specialised submersibles; these are expensive and can only be for limited periods of time. Much knowledge has been gained from such expeditions, e.g. what species are present in the deep sea, what conditions are like and even some observations of inter and intraspecific interactions. Bringing specimens to the surface has provided some information on species anatomy, physiology and behaviour; however the change in pressure often leads to deformation reducing the reliability of any observations.
From observations of closely related species found in shallower waters, in situ or in vitro (Herring 1990) and a few terrestrial species, such as the firefly’s, three behavioural functions have been identified (Young 1983, Morin 1983):-