I saw a documentary on this. It seems that fertilizer used on farms, runs off the farm land and into the sea during the rainy season. This has caused an explosion of a certain kind of starfish that eats the live coral, leaving behind the bleached exoskeletons of the old coral.
Local problem with a local solution...but there is no money in that.
Here is a link to the story of the starfish, for those who are interested.
http://www.treehugger.com/files/2008/01/killer_starfish.php