Coral reefs have been in existence for many thousands of years and have survived and evolved through massive climate changes. Climate change (specifically global warming), by itself is therefore unlikely to result in the global elimination of coral reefs and there are few instances where such changes on their own have led to reef destruction. It is likely, however, to result in changes to reefs which will adversely affect local communities dependent on reefs for their livelihood.
Unfortunately global warming is not the only factor currently causing stress to coral reefs. Many reefs are being degraded or destroyed by pollution and sedimentation, over-exploitation of fish and other species and physical destruction. The worry is that these chronic and acute stresses to which coral reefs are not well adapted may act synergistically with climate change and threaten the existence of coral reefs in many parts of the world. Stressed reefs lose their natural ability to recover from disturbances such as cyclones and increased water temperature, both of which could increase in frequency as a result of global climate change.
Specific climate-change threats to reefs identified in a recent report on the implications of climate change on coral reefs (Wilkinson and Buddemeier, 1994) include the following:
(a) Although rising sea levels will not threaten most coral reefs themselves, since they can grow upwards, low-lying islands associated with reefs would be affected. In the Maldives, the government is already seriously considering the implications.
(b) Frequent episodes of temperature extremes, caused by climate change, will cause coral bleaching (see below), loss of coral cover and a lessening of the ability to withstand other stresses.
(c) As concentrations of CO2 in the atmosphere increase, so more CO2 will dissolve in the surface layers of the sea. The resulting increase in acidity may slow down the rate at which corals and coralline algae can deposit calcium carbonate. In contrast, an increase in the concentration of CO2 stimulates the growth of algae which might then out-compete the corals. Overfishing and nutrient pollution will exacerbate the latter effect.
(d) Reefs adjacent to land masses will be affected by increases or changes in rainfall and runoff. Greater sediment loads and an increase in both pollutants and nutrients in coastal water could damage reefs.
(e) Shifts in current patterns could have serious impacts on reefs.
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