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. Other possible causes of coral bleaching include increased solar radiation, decreased salinity, sedimentation due to coastal development and run-off, and exposure to air at low tides or low sea level. It is also possible that pollution by copper, herbicides and oil can contribute to the bleaching as the pollutants can make the coral increasingly vunerable. Their studies have shown that the incidence of bacterial diseases correlates with changes of season and temperatures. Some coral species tend to grow fast and have high metabolic rates.