Coral Bleaching

Coral reefs owe their brilliant colours to tiny algae that live inside the coral's tissue. These algae photosynthesize and pass most of the resulting energy to their host, while the coral offers shelter and nutrients in return. When the surrounding water grows too warm, this partnership breaks down: the stressed coral expels its algae and turns a ghostly white, an event known as bleaching. A bleached coral is not yet dead, but it is starving, since it has lost its main food source. If cooler conditions return quickly, the algae can recolonize the tissue and the coral may recover. Prolonged heat, however, leaves the coral too weak to feed, and large stretches of reef can perish. Because reefs shelter a quarter of all marine species, their loss ripples outward through entire ocean ecosystems.