As coral reefs are put under increasing stress from rising sea temperatures, some believe that a potential refuge could be the ‘deep blue sea’. However, scientists have now discovered that to thrive under those conditions, corals must possess a fluorescing ability which allows them to seemingly produce their own sunlight.
It is well known that many shallow reef corals fluoresce in sunlight for protection against harmful UV radiation. As symbiotic organisms, most corals need microscopic algae to survive. This algae, also known as zooxanthellae, consumes the waste products from the coral whilst providing the coral with most of its nutrients through photosynthesis. Too much UV radiation can damage the algae, starving the corals from nutrients. Fluorescence produces certain proteins which protect their algae friends from the sun.
Researchers from the University of Southampton were therefore surprised to see that deep-sea corals fluoresce for the opposite reason to shallow reef corals. Using deep-sea coral samples, the team found that when they fluoresce the colour red, they have a better survival rate. Red light promotes photosynthesis as the algae can absorb it more effectively, explaining why they convert deep-water blue light into this red light. This red fluorescence is then dispersed in the coral and reflected by the calcium skeleton, making it look like they are creating their own sunlight. They essentially amplify the little sunlight they have access to, by using this ability to fluoresce.
Published in Proceedings of the Royal Society B, this study sheds important light on coral biology. There are many coral reefs around the world that are seriously endangered due to rising temperatures as a result of climate change. It has been thought that the ‘deep blue sea’ could be a sanctuary for these struggling species. However, unless they can adapt their fluorescing ability to dark waters, it seems this might not be a viable option. It gives further incentive to find other innovative ways of protecting their shallow water homes.
Sarah Barfield Marks is studying for an MSc in Science Communication
Banner image: coral colony, Sanakaaa