From Azimuth:

Global warming has been causing the "bleaching" of coral reefs. A bleached coral reef has lost its photosynthesizing symbiotic organisms, called zooxanthellae. It may look white as a ghost — as in the picture above — but it is not yet dead. If the zooxanthellae come back, the reef can recover.

With this year’s record high temperatures, many coral reefs are actually dying:

• Dan Charles, Massive coral die-off reported in Indonesia, Morning Edition, August 17, 2010.