Coral reefs are among the most ancient of ecosystem types, dating back to the Mesozoic era some 225 million years ago. Modern reefs can be as much as 2.5 million years old.
Although they cover only a tiny fraction (less than 0.2%) of the ocean's bottom, coral reefs capture about half of all the calcium flowing into the ocean every year, fixing it into calcium carbonate rock at very high rates. Coral reefs release carbon dioxide to the atmosphere due to the chemistry of calcium carbonate precipitation. The release of carbon dioxide from coral reefs is very small (probably less than 100 million tons of carbon per year) relative to emissions due to fossil fuel combustion (about 5.7 billion tons of carbon per year).
Coral reefs store very little organic carbon and are not very effective "sinks" for carbon dioxide from the atmosphere. Forests are more effective sinks for atmospheric carbon because they convert carbon dioxide into long-lived structures: trees.
Biological And Economic Values
Coral reefs are among the most biologically diverse ecosystems on the planet. Although tropical rainforests contain more species than coral reefs, reefs contain more phyla than rainforests. Phyla are large groupings of organisms that are thought to be related. Covering less than 0.2% of the ocean floor, coral reefs contain perhaps 1/4 of all marine species. New studies indicate that biodiversity on coral reefs may be even higher.
Despite their limited area, coral reefs may be home to up to 25% of the fish catch of developing countries or 10% of the total amount of fish caught globally for human consumption as food. Reefs are also extremely valuable as breakwaters and draws for tourism.
Coral reefs are among the most endangered ecosystems on earth. Coral reefs in 93 of the 109 countries containing them have been damaged or destroyed by human activities. In addition, human impacts may have directly or indirectly caused the death of 5-10% of the world's living reefs, and if the pace of destruction is maintained, another 60% could be lost in the next 20-40 years.
The most important short-term threats to coral reefs are sedimentation (from poor land use such as clearcutting on steep slopes and other activities such as dredging without silt curtains), eutrophication (over-fertilization caused by excessive fertilizer use and sewage pollution), and overfishing. Destructive fishing techniques such as fine mesh nets, cyanide poisoning, and dynamiting are common in coral reefs, and have actually come to dominate fishing in parts of Indonesia and the Philippines. Physical damage to coral reefs by scuba divers and tourists would probably be a minor threat if the number of visitors to reefs were limited to moderate levels and if water quality was always high enough to support rapid recovery of corals. However, tourism often results in large numbers of visitors, which leads to extensive physical damage, sewage pollution, and other adverse water quality impacts which slow or eliminate recovery.
Coral reefs in every major tropical region of the world bleached white during the mass bleaching events of the 1980's. This bleaching depresses coral growth rates and in some cases results in mass coral mortality and enormous aquatic population loss, and can even contribute to potential species extinctions. Bleaching is caused by a variety of factors, including siltation and changes in salinity resulting from poor land use, pollution, and slight increases in temperature. Coral reefs may bleach even more extensively if global warming continues unabated.
The United Nations Framework Convention on Climate Change and the United Nations Convention on Biological Diversity, both signed at the 1992 Rio Earth Summit, seek to protect sensitive ecosystems from the effects of climate change and to enhance protection of areas of high biological diversity such as coral reefs.
A new focus by pharmaceutical firms and scientists on coral reefs as a source of new medicines may generate a new form of sustainable development in coral reef areas. This will be contingent upon the continued development of a trend toward contracts designed to compensate less developed countries, indigenous peoples and other affected parties for intellectual property and genetic resources used to develop medicines, thereby creating economic incentives to protect biological diversity.
Marine fisheries reserves have proven to be effective in restoring and maintaining fisheries resources. For example, the establishment of the Sumilon Island Reserve in the Philippines resulted in about twice the density of fish than in adjacent areas after 9 years of protection. The catch-per-unit-effort was also about twice as high while protective measures were in effect compared to a period when they were not. Small scale waste treatment systems, employing both biological and chemical methods, are available for cost-effective treatment of sewage that will protect water quality in coral reef areas. Other measures can also reduce nutrient pollution. For example, an ordinance restricting phosphate levels in detergents was adopted recently in the Florida Keys. It will likely result in a 50% reduction in phosphate pollution from septic tanks. Phosphate pollution contributes to algal blooms and coral death in many coral reefs.
Marine sanctuaries, such as Australia's Great Barrier Reef Marine Park and America's Florida Keys National Marine Sanctuary, can be effective management tools if properly implemented with the meaningful participation of resource users, citizens, scientists, and environmentalists. Sanctuaries need effective research, administration and enforcement to work.