In the past 20 years, nearly a third of the world's coral has been destroyed. Around 90 percent of the reefs off the coasts of Sri Lanka, Tanzania, Kenya, the Maldives and the Seychelles are at risk. If ocean temperatures rise by another 7ºF in the next three decades, as is predicted, 95 percent of the Great Barrier Reef will disappear. The primary cause of the die-off is coral bleaching. As temperatures rise, marine bacteria flourish and attack the algae that live symbiotically within every individual coral polyp. The algae photosynthesize sunlight into energy (in the form of sugars) for their hosts and give coral its color. When the algae dies, what's left is a ghostly white.