Underwater Vision
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.
