Coral Reefs

            Coral bleaching is the whitening of coral colonies due to the loss of symbiotic zooxanthellae from the tissues of polyps (Guilcher 1988). This loss exposes the white calcium carbonate skeletons of the coral, yet coral naturally lose about 0.1% of their zooxanthellae during regulation and replacement processes. However, adverse changes, such as increased temperatures, disease, excess shade, pollution, salinity changes, increased levels of ultraviolet radiation, and sedimentation, can cause an increase in the number of zooxathellae lost. Although the exact mechanism by which corals bleach is unknown, there are a number of hypotheses that attempt to answer the question. It is thought that there is an imbalance between the coral and algae plants that live inside the coral tissue. Thus the coral reacts expelling the algae and eventually lose its color, appearing "bleached".
             Coral reefs are extremely sensitive, slight changes in the reef environment may have detrimental effects on the health of the coral polyps. There are numerous changes, but they generally fall into two categories: natural disturbances and anthropogenic disturbances (Guilcher 1988). Of these two categories anthropogenic disturbances are avoidable and are linked to the vast majority of decreases in the coral health. Threats such as human expansion, development, fishing techniques, erosion, and pesticide use, all interfere with the growth of healthy coral polyps and are classified into the latter category. .
             Oceanographers say that the El Nino weather pattern of 1998, which led to a rise in water temperature by up to six degrees Fahrenheit, did enormous damage to the reefs (Anon). It is estimated that in another twenty years, water temperatures are likely to rise to the point where coral will be unable to survive. 1998 was the warmest year on record and brought the most devastating coral bleaching to date, every reef system in the world was affected.