This animation zooms into a coral reef to explore the tiny animals that build reefs, the photosynthetic algae inside their cells, and the damaging process of coral bleaching. Corals get much of their energy from symbiotic algae that live inside their cells. When ocean temperatures rise beyond a certain threshold, the algae’s photosynthetic machinery may be damaged and produce harmful reactive oxygen molecules. This animation shows how corals subsequently eject their algae in a process called coral bleaching, which causes the corals to turn white and often eventually die.