Bioluminescence in plankton and nekton

Bioluminescence is the capacity of living organisms to emit visible light. In so doing they utilise a variety of chemiluminescent reaction systems. It has been historically confused with phosphorescence and the latter term is still frequently (and erroneously) used to describe marine bioluminescence. Some terrestrial species (e.g. fireflies) have the same ability but this adaptation has been most extensively developed in the oceans. Bioluminescent species occur in only 5 terrestrial phyla, and only in one of these (Arthropoda, which includes the insects) are there many examples. In contrast, bioluminescence occurs in 14 marine phyla, many of which include numerous luminescent species (Table 1). All oceanic habitats, shallow and deep, pelagic and benthic, include bioluminescent species, but the phenomenon is commonest in the upper 1000m of the pelagic environment.