Corals Wear Fluorescent Sunscreen

Kevin Robinson

It may not be Coppertone, but it works. Scientists from the University of Sydney and the University of Copenhagen in Denmark have discovered that the fluorescent pigments in some corals protect them against sunlight and may help them survive the mass episodes of coral bleaching associated with global climate change.
Corals depend on a symbiotic relationship with dinoflagellate algae. They give the algae a home, and the algae reciprocate by providing nutrients. Stripped of their dinoflagellate roommates, the corals die.

The researchers, who published their findings in the Dec. 14, 2000, issue of Nature, studied the location of the fluorescent pigments in the corals, how fluorescence energy coupling and transformation work between them, how the concentration of pigments relates to corals' exposure to sunlight and how coral tissue scatters light. They also compared how well the fluorescent and nonfluorescent varieties of the same species can tolerate intense light.

Energy transfer

Some fluorescent corals house the pigments in layers above the dinoflagellates, where they can absorb excessive sunlight before it damages the symbionts, explained Sydney's Anya Salih, a postdoctoral fellow on the team. Once intercepted, the ultraviolet and blue light is converted through a fluorescence energy transfer chain to yellow and red wavelengths, which are less dangerous because they are not absorbed by the dinoflagellates' photosynthetic apparatuses. These corals, the researchers suggest, may be able to survive and repopulate reefs damaged by warming oceans and by the higher UV levels attributable to ozone depletion.

Salih and her colleagues Guy Cox and Anthony Larkum have begun a three-year project to explore the ability of corals to adjust to changes in the global climate.

"The question of whether corals have the potential to adapt to global climate change is of primary concern not only to scientists," she said, "but also to reef managers such as the Great Barrier Reef Marine Park, tourism and fisheries industries, and the general public."