Coral turns pale when the colourful algae living inside its tissues are expelled during warm spells.

The longer version

Warmth damages the working partnership between coral and the pigmented algae living inside its tissue. Those algae supply much of the host's food through photosynthesis, and their pigments give the colony its colour. Heat disrupts their machinery, so the host expels them, and pale limestone shows through transparent flesh.

Bleached coral is alive but starving, and it recovers if temperatures drop soon enough. Prolonged heat kills tissue outright. Sensitivity varies by species, depth and current, and colonies that have weathered past warm spells often cope better than those meeting heat for the first time. Recovery also depends on clear water and on grazers keeping seaweed from covering bare skeleton.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.