Why did the symbiotic algae leave home?

The algae called zooxanthellae living in the coral polyps were even fussier about their living conditions than scientists had expected.

Scientist thought there was a problem when the coral polyps lost their colour. The actual colour of a polyp is white. It is the zooxanthellae that make coral colourful.

Scientist discovered the white coral polyps had lost most of their zooxanthellae. Some zooxanthellae were left behind. These did not appear healthy as they were not very interested in producing food.

When the polyps turned white, the sea temperature was warmer than normal so scientists investigated if there was a link. They found that only a small increase of seawater temperature above normal caused coral to loose its colour. After more investigation they found when the temperature increased the coral polyp seemed to go into panic mode and expelled most of the zooxanthellae.

Are the coral polyps trying to commit suicide by throwing out their zooxanthellae or is there a deeper problem?

Sick Coral

Sick coral