Bioluminescence

Abstract

In the early days of marine biology, a century ago, when many new species were being discovered, scientists were puzzled by strange organs that some of these animals possessed. Various functions were ascribed to them, such as pressurereceptors, infra-red detectors and accessory eyes. It is now known that many of these puzzling organs are photophores or light-organs. Deep-sea animals possess the same sensory modalities as surface and shallowwater species—smell, sight, hearing, vibrational sense, touch. Sensory organs may be accentuated or specialized in certain ways to make them more efficient in the peculiar conditions obtaining in deep waters. Signals which animals emit are sounds, low-frequency vibrations, odours and light. In an environment where perceptible daylight is wanting, light is produced by the animals themselves. Very many deep-sea animals have well-developed eyes: to function these eyes need light, and the light is provided by luminescence. It is now apparent that luminescence is a wide-spread and common phenomenon in the deep sea. The abundance, complexity and wide distribution of light-organs among bathypelagic animals attest to this. In an intensive investigation of a small area near Bermuda, Beebe (1937) found that two-thirds of the species of deep-sea fish captured below 700 m were luminous; reckoned as individuals, over ninetenths were luminous. This high proportion of luminous fish was due to the numerical abundance of cyclothonids and myctophids in the catches.