The health, diversity and extent of corals, and the geochemical makeup of their skeletons, record a variety of changes in the ocean surface water. Corals in coastal waters are susceptible to rapid changes in salinity and suspended matter concentrations and may be valuable indicators of the marine dispersion of agricultural, urban, mining and industrial pollutants through river systems, as well as the history of contamination from coastal settlements.
Corals respond to both natural changes in the marine environment and to anthropogenic pollution.
Annually or longer, depending on the record sought. The complexity of environmental correlations requires very careful sampling and a high degree of analytical expertise. They are an invaluable source of paleoenvironmental information for tropical coastal areas and the shallow marine realm. Threshold values are difficult to quantify, particularly when more than one property is changing, and may vary from site to site as a consequence of reef adaptation to local conditions. The timing of growth hiatuses within living colonies and of mass mortality events can, however, be useful in inferring past severe and catastrophic disturbances.