Coral Bleaching
The biggest threat to coral reefs is coral bleaching from rising ocean temperatures.
When water gets even 1-2 degrees above normal for too long, stressed coral expels its zooxanthellae algae. Without the colorful algae, coral turns ghostly white — bleaching.
Bleached coral is not dead yet but is starving without its algae food source. If temperatures return to normal quickly, algae can return and coral recovers. But prolonged heat kills the coral.
In 2016-2017, the Great Barrier Reef lost about 50% of its coral to back-to-back bleaching events. Similar events have hit reefs worldwide with increasing frequency.
Scientists predict that if temperatures rise more than 2 degrees Celsius, over 99% of reefs could be lost.
**Important:** Bleaching is a warning sign — if we act to reduce warming, many reefs can still be saved.