Corals are to the oceans what tropical rainforests are to land. Known as Neptune's goblets, they are a vital link in the marine ecosystem and, in fact, store more biodiversity than the rainforests. But human activity is gobbling them up. And global warming is making matters worse. Bleaching and coral disease outbreaks are increasing in frequency, intensity and range. And reefs in the Indian Ocean are said to be the worst-affected. Are corals dying to tell us something?