I do a lot of scuba diving, and I love coral reefs. They are probably the most beautiful things you can see under water, and they are usually teeming with fish and other wildlife. While there are other wonderful things to see in the ocean, I can’t think of anything better than nearly depleting a tank of air while slowly swimming over and around a coral reef.
However, there are times when coral reefs aren’t so beautiful. Compare the picture above, for example, to the following picture:
What’s the difference? The coral pictured above has bleached.
Corals have an amazing mutualistic relationship with microscopic algae called zooxanthellae. The corals provide protection and certain necessary chemicals to the zooxanthellae. In exchange, the zooxanthellae make oxygen, sugar, and other chemicals for the corals, and they also help the corals remove waste. It is a relationship that works wonderfully for both of them. However, there are times when corals expel their zooxanthellae. This causes them to turn white (as shown in the picture above), which is why it is called “bleaching.”