Marine mammals are able to see well underwater if conditions are right, but even in the clearest water, the range is severely limited compared with that in air. Cetaceans and pinnipeds such as the California Sea lion and the Bottlenose dolphin have evolved visual systems that are adapted to the different way in which light travels through water. Long wavelengths such as red and orange light are absorbed quickly by water and therefore don’t travel far; whereas green, blue and particularly ultraviolet light penetrates much further. Sea lions and dolphins have lost the ability to see red, orange and yellow light but are very proficient at discriminating between blues, greens and grey colours. They can also see exceptionally well in dim light and an interesting physical system in their eyes enables them to quickly adapt to very bright light when they come to the surface.

While light levels generally decrease rapidly the deeper you go in water, there are surprising sources of light even at extreme ocean depths that include bioluminescence whereby organisms produce light via a biochemical process (similar to fireflies on land), and also fluorescence where light falling on an organism is changed to a longer wavelength and the organism appears to glow.

Corals are among the most common fluorescent organisms in our ecosystem. Corals thrive in shallow tropical waters and are therefore exposed to intense solar radiation including ultraviolet light which causes serious damage to unprotected biological systems. However, it has been speculated that corals are able to absorb some of this harmful ultraviolet radiation with the help of fluorescent pigments in their soft tissues and convert it into less damaging visible light.

Many different marine organisms, for example, marine algae, shrimps, anemones and fish also fluoresce and this is a property of their biochemical composition. (This phenomenon is not limited to marine organisms and living organisms as diverse as mushrooms, humans (for example, our teeth), and common household items such as peanut oil also  fluoresce!)

 In addition to studying the visual ability of some marine mammals, MMRL has identified this new research area of fluorescence in marine organisms as a fascinating topic well worth further investigation. Using equipment purchased from NightSea, we have, within the broader topic of underwater vision, conducted pilot studies of underwater fluorescence and collected data from Singapore, Malaysia, Indonesia and the Maldives. The aims of this new and exciting research area are as follows:

• To study the occurrence and spectral characteristics of underwater fluorescence

• Understand the biological importance of the phenomenon

• Develop improved methods of assessing the health of marine ecosystems based on fluorescence as an additional indicator

• Investigate how fluorescence might help behavioural scientists study the behaviour of marine animals.