What is Coral Bleaching?

Coral reefs are famous for their brilliant colors. What many people don’t realize is that the coral themselves are white. They get those fabulous colors via a symbiotic relationship with tiny plants called zooxanthellae that usually live inside the coral. Like all plants, zooxanthellae use photosynthesis to turn light to chlorophyll, which is responsible for coral’s green and brown colors. This process also produces carbohydrates (which the coral uses as food) and oxygen. The brighter the coral, the more oxygen is being produced.

Coral also produces protein pigments referred to as “chromoproteins”. These pigments can be red, purple, or blue, and are often what’s responsible for making the white corals appear colorful. These pigments play a major role in the health and resilience of the corals by protecting them from excessive stress. There are also fluorescent pigments in cyan, green, yellow or red, that glow when viewed with certain types of lights.

The problem is that coral are picky. They’ve evolved to live in a very specific environment, especially when it comes to water temperature. Not all coral are the same, and they can survive some temperature fluctuations. However, it’s safe to say that they do best in water temperatures between 20–32° C (68–90° F).