While it is known that most corals require a certain amount of sunlight in order to survive, in certain shallow reef ecosystems, light levels are often higher than required by corals. These higher light intensities can often be detrimental to the corals and algae in which the corals have a symbiotic relationship. Researchers with the University of Southampton have discovered how Acropora nobilis corals use their colors as sunscreen to protect themselves against harmful sunlight.
These corals have developed a sunscreen against these levels of light in the form of pigments of differing colors. With the Great Barrier Reef serving as the laboratory for their studies, the researchers created experimental evidence that showed the pink and purple chromoproteins act as sunscreens for the symbiotic algae in the corals by removing light that may be harmful to the corals.
Dr. Jörg Wiedenmann, head of the University of Southampton’s Coral Reef Laboratory and senior lecturer of biological oceanography says that these pigments, called chromoproteins, screen the corals from harmful light while also helping beneficial algae enter new tissues in the corals in which they are present.
“The beautiful pink and purple hues that are produced by the coral host are often evoked by chromoproteins; pigments that are biochemically related to the green fluorescent protein (GFP) of the jellyfish Aequorea victoria. In contrast to their green glowing counterpart, the chromoproteins take up substantial amounts of light, but they don’t re-emit light,” Wiedenmann said in a statement released by the university. “GFP-like proteins were suggested to contribute to the protection of corals and their symbionts from excess sunlight. This hypothesis has been controversially discussed as the mechanism as to how these pigments function remained unclear. At least for the chromoproteins we know now that they have indeed the capacity to fulfill this function.”
The researchers also say that the reason some corals build up high amounts of chromoproteins in areas of growth such as branch tips and spots where wounds have occurred is due to increased light intensities. The corals can switch on genes that produce the chromoproteins that act as sunscreens.
“These growing areas contain essentially no symbiotic algae, so much of the light is reflected by the white coral skeleton instead of being used by the algae” said Wiedenmann.