Once vibrantly colored and teeming with life, many coral reefs around the planet are now bleached and barren, thanks to a condition called coral bleaching. Their color drained, bleached reefs stand like skeletons along the world’s coastlines, from Australia and Madagascar to the Persian Gulf and the Caribbean Sea.

But coral bleaching is much more than an aesthetic loss. It is an environmental indicator: an omen of starving animals, a failing ocean ecosystem and a devastating change in global climate. Rising ocean temperatures are the fundamental cause. But before we can understand why these beautiful coral ecosystems are now at risk, we have to understand how they got their radiant color in the first place…

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