Australia's magnificent Great Barrier Reef relies entirely on a highly unstable microscopic alliance where starving coral polyps enslave photosynthetic algae called zooxanthellae…

A closer look

A beautiful tropical reef isn't a peaceful paradise; it is a ruthless microscopic hostage situation. Tropical ocean waters are essentially biological deserts lacking raw nutrients. To survive, the coral animal physically ingests millions of tiny dinoflagellates called zooxanthellae and houses them inside its own transparent tissue. The algae get a safe fortress and carbon dioxide, while the coral heavily taxes them for the sugars they produce from the sun. The moment the water gets slightly too hot, this tense alliance collapses, the coral violently ejects the algae, and the reef bleaches pure white.