When normally colorful coral reefs turn white, it's a sign of stress in the ocean environment. But over the past fifteen years, in many of the world's major coral reefs, scientists have seen some of this color disappear. But over the past fifteen years, in many of the world's major coral reefs, scientists have seen some of this color disappear. Most reef-building corals are clear with white skeletons. The colors come from tiny, single-celled algae that live in a coral polyp's cells.
Corals provide shelter and nutrients for the algae.
In return, the algae convert sunlight to chemical energy for the corals. Photo courtesy of Craig Quirolo, Reef Relief. So what do bleached corals have to say about possible upcoming climate changes. More on that subject tomorrow. We have more on coral bleaching .