New York Times
OBSERVATORY
By HENRY FOUNTAIN
Published: August 31, 2004
Destroying Coral's Color
Bleaching of coral reefs has become a worldwide problem, and it is often linked to rising ocean temperatures. A local increase of as little as 3 degrees Fahrenheit can cause the death of symbiotic algae that, among other things, give the coral its color.
While it is known that higher temperatures disturb photosynthesis in the algae, resulting in an increase in peroxide, carboxyl radicals and other reactive molecules that can kill cells, the exact mechanism by which this happens has been unclear.
But new work by Paul G. Falkowski and others at Rutgers University shows what is going on. Higher temperatures, they report in The Proceedings of the National Academy of Sciences, damage thylakoid membranes, components at the heart of the photosynthetic process.
Thylakoid membranes are thin structures, composed primarily of fats, that are stacked in the algae's chloroplasts. Within the membranes are the chlorophyll and other compounds responsible for photosynthetic reactions, including the stripping of water to create electrons, hydrogen ions and oxygen.
In their experiments, the researchers found that heat affected the ordered stacking of the membranes, which is crucial for efficient energy transfer among the different parts of the process. The membranes were still capable of splitting water, but the transfer of the electrons was disrupted. This eventually resulted in the production of lethal amounts of reactive oxygen molecules.
The researchers found that those membranes that were sensitive to heat had a different composition of fats from those that could tolerate higher temperatures. So they say that analyzing the fat content of membranes may be a way to determine whether certain reefs will be susceptible to bleaching.
