What causes coral bleaching?

Coral bleaching primarily occurs due to rising sea temperatures, a phenomenon closely linked to climate change. Corals have a symbiotic relationship with tiny algae known as zooxanthellae, which live within their tissues and provide them with food through photosynthesis. When sea temperatures rise beyond the normal range, corals expel these algae to protect themselves from stress, leading to a loss of color and essential nutrients — this is what we refer to as coral bleaching.

This response to thermal stress is harmful because without the zooxanthellae, corals not only lose their vibrant colors but also become more susceptible to disease and mortality. When prolonged, this situation can lead to widespread coral death, severely impacting marine ecosystems as well as the benefits these reefs provide to human communities, such as coastal protection and tourism.

While pollution, overfishing, and coastal development can negatively affect coral reefs, their direct impact in causing coral bleaching is less pronounced compared to the significant effects of rising sea temperatures. Each of these factors contributes to reef degradation or inhibits recovery, but the immediate trigger for the bleaching phenomenon itself is predominantly the increase in water temperature.