Certain wavelengths of light from the sun will penetrate deeper into the ocean than others. On a coral reef, it is the red wavelengths which are filtered out by the water. The coloration is bluish-green at depths greater than 30 feet.
But a recent study headed by Professor Michiels from the University of Tübingen in Germany has revealed that red as a color is still highly significant to many of the reef’s inhabitants. Michiels’ team has discovered that at least 32 reef fish, representing some 16 different genera and 5 separate families, all possess the ability to give off red light. The resulting pattern of red fluorescence is very distinctive, sometimes being restricted to specific parts of the body, often in the vicinity of the head.
The fish which can fluoresce generally proved to be smaller species such as gobies, which frequently occur in pairs. They are not powerful swimmers and tend to hide away. This biofluorescence allows individual fish to recognize and communicate with other members of their species. They are able to see this distinctive light, which we can only pick up using a special filter.
Their fluorescent patterning then stands out, being as distinctive as ordinary red markings would be in sunlight. In some cases only small areas of the body, such as rings around the eyes or areas of the fins, are illuminated, which may afford some protection against predators.
Nor is it just fish that possess an ability to communicate in this way. Many reef invertebrates also glow red in this environment. This applies to a number of different corals, various sponges, feather stars and polychaete worms.
Video courtesy © Michiels et al. BMC Ecology 2008
To read the full study, click here.