Ammonia, and phosphates are provided by the planktonic animals, on which the coral feeds, and is supplied to the algae as waste products. In return the algae produces oxygen, glucose, glycerol and alanine to the coral by photosynthetic processes. These chemical compounds are then used by the coral for metabolism, and the production of carbohydrate, lipids and protein. The relationship also enables the coral to synthesise and deposit its calcium carbonate skeleton. The cause of the loss of photosynthetic zooxanthellae and the resultant coral bleaching is unknown at present but thought to be due to an increase in ocean temperatures.
Coral polyps are only able to tolerate a small temperature range.
A 1oC rise in sea temperature can cause bleaching. If the Earth s temperatures are rising, the ocean will also become warmer. Sea temperatures are also thought to rise due to the El Nino Southern Oscillation, which occurs when the trade winds weaken. Stochastic events are the random, unusual weather conditions such as wind direction and speed. But, this is probably unlikely to contribute to ocean warming without the influence of other factors.