What causes coral bleaching in the Great Barrier Reef?

The primary cause of coral bleaching in the Great Barrier Reef is elevated seawater temperatures, often exacerbated by El Niño events. This heat stress causes corals to expel their symbiotic algae, known as zooxanthellae, which provide them with color and nutrients through photosynthesis.1234

Other contributing factors to coral bleaching include:
* Changes in seawater chemistry, such as ocean acidification due to increased carbon dioxide absorption.315
* Increased levels of sediment or pollution in the water.31
* Exposure to ultraviolet radiation.31
* Chemicals from sunscreens and personal care products.3

When zooxanthellae are absent for extended periods, corals can die, leading to a decline in reef biodiversity. Climate change is identified as a major threat to coral reefs worldwide due to its role in rising ocean temperatures and acidification.32