Coral are literally starving to death due to rising ocean temperatures and increased levels of acid in the ocean which are killing the algae; their food source. This combined with the heat, stresses the coral until it turns white and bleaches.
In December 2016, Australia must report back to UNESCO on the health of the Great Barrier Reef. Right now the outlook is bleak, but it doesn’t have to be. There is still time to save the Reef.