Coral reefs are the marine versions of tropical forests. They are the world’s most biologically diverse marine ecosystems. Of all the vital coastal ecosystems under threat, it is coral reefs which are being decimated faster than any other marine resource. It is possible that they are being extinguished more rapidly than rainforests. Although there are estimated to be 600,000 sq km of coral reefs in the world, with 30 percent concentrated in Southeast Asian seas, their condition is thought to be deteriorating nearly everywhere, but more particularly around the shores of developing countries. Wherever coral reef surveys were carried out in the recent years, the results have been disheartening. According to some estimates, 58 percent of earth’s coral reefs are at high or moderate risk from overexploitation, coastal development, and pollution (National Ocean Service 47).
Coral reefs rival tropical rainforests in species richness and diversity. These spectacular living systems are a very important aspect of the marine environment (Ravilious, Spalding 9). The 150-km long barrier-reef surrounding Palau in the Pacific, for example, has nine species of seagrasses, more than 300 species of coral, and 2,000 varieties of fish. The Great Barrier Reef of Australia has 400 species of coral providing habitat for over 1,500 species of fish and 4,000 different kinds of mollusks. Nearly one-third of all fish species live on coral reefs, while others are dependent on reefs and seagrass beds for various stages in their life cycles.
Coral reefs are among the oldest living communities of plants and animals on earth, having evolved about 450 million years ago. That is why their destruction is all the more tragic. Most modern coral reefs are between 5,000 and 10,000 years old, many of them forming thin layers over older, much thicker reef structures dating several million years. Most of the reef colony is actually dead, a skeleton framework. Only the upper layer is covered by a thin changeable living skin of coral. Coral polyps — the animals that build reefs — are the master builders of the sea, constructing their homes upon the remains of their predecessors.
Although estimates as to the amount of fish that can be harvested from reefs varies from 1-30 tons per sq km per year, a sustainable harvest of some 15 tons per sq km of fish, mollusks and crustaceans should be possible. Almost 90 percent of all fish caught by artisanal fishermen in Indonesia are reef-dependent, as are some 55 percent of the fish consumed by Filipinos. The potential yield of fish from coral reef waters is estimated to be in the region of 9 million tons — more than 10 percent of the global level (Crump 66). Coral reefs provide protection to the coast and abundant resources for the people who live near them.
Having survived hundreds of millions of years, coral-reef ecosystems are clearly robust (Birkeland 355). Yet in our age of heavy environmental degradation, their fragility is exposed. Indeed, when it comes to coping with change, reefs are fragile environments that cannot tolerate a wide range in conditions. Turbidity, temperature, and water depth have to be controlled tightly in order to support healthy reefs. Many environmental factors can lead to their demise. They are facing great problems rising from human activity. Chemical pollution, organic pollution, thermal pollution, turbidity, and physical destruction are some of the sources. Some of the byproducts of the increase in coastal development are having negative impacts on coral reefs. Pollution from human waste disposal, global warming, and other natural hazards are all causing problems for these reefs.
Fringing and barrier reefs tend to be most vulnerable to human impact because of their proximity to land. Atolls typically have little or no population on or near them. There are, however, human generated problems on atolls. One of the most well known is the nuclear bomb test in the southwest Pacific by France and the United States. French tests have continued in the face of widespread protests from other countries and various environmental groups. Military activities in general have been a severe problem for atoll reefs because of the widespread operations on them.
Mining activities have also been conducted on reefs. The coral, sand, and gravel have been taken for various uses, especially for construction. The blasting that is frequently used also kills many of the fish. In some of the island reef areas dynamite is actually used as a means of fishing. Coral mining and blast fishing are particularly destructive since most coral species grow very slowly. Coral reefs are like oases in the desert; once destroyed, the habitat reverts to “desert”, where only a tiny fraction of their former inhabitants can survive. Another destructive activity is the collection of corals for sale to tourists.
The biggest problem for reefs come from the water and its contents. Because reefs require warm, clear, pure seawater, any deviation form this high quality may cause problems. Suspended sediment can be a problem for all filter feeders on the reef and can reduce light penetration for photosynthesis. This may be caused by dredging nearby. Another source of turbid water that might influence reef environments is runoff from the adjacent mainland. Rainfall in the tropics is generally high and summer or monsoonal rains can cause tremendous amounts of runoff that carries large quantities of sediment. Much of the sediment will be in suspension as it moves into the shallow marine environment and will cause serious problems for reefs.
A combination of improper land management, especially deforestation of coasts and uplands, and outright destruction through coral mining and blast fishing are devastating the delicate coral ecosystems. As forests are cut down for timber and to make room for more agricultural land, huge quantities of erosion sediment can be flushed off the land and into shallow coastal waters. Without mangrove forests to trap the sediment, it is often transported to coral colonies, where it suffocates the living polyps. Sedimentation of reefs can transform thriving communities into dead ones. When forests are converted to farmland, the run-off of nutrients is greatly accelerated. Nitrogen and phosphorus poison corals and reduce their ability to compete with other organisms, such as algae.
Chemical pollutants can be a major limiting factor in reef distribution and can kill existing reefs. Nutrients can be a limiting factor if present in large quantities. There is a concern about reefs in the Florida Keys, for example, because of the ever-increasing domestic sewage causing nutrients to be dumped into the marine environment. The same situation exists on some heavily developed areas of island as Tahiti. Other types of chemical pollution include various types of industrial waste that is accidentally or purposely released into the near-shore environment where reefs are present.
Overfishing can also lead to outbreaks of coral predators, resulting in the massive mortality of corals. Over the past four daces, there have been several outbreak of the coral-eating crown-of-thorns sea star in the western Pacific Ocean. In places, coral mortality adjacent to aggregations of the sea stars approached 100 percent.
Due to environmental havoc happening in our day, previously unknown coral diseases, such as black-band disease and white-band disease, have also been plaguing coral reefs on a global scale (Sumich, Morrissey 267). Further, the phenomenon of coral bleaching, which refers to loss of color due to the expulsion of symbiotic unicellular algae, can be caused because of global warming and a wide variety of other reasons. Coral bleaching is increasingly being associated with coral destruction since the 1980’s. In the near future, the rise of sea-levels due to global are expected to present a grave problem to the coral communities, as the rise in water level would affect the penetration of light vital to coral health.
There is much that can be done to slow or end the global destruction of coral reefs that we are experiencing today. However, efforts to manage and protect the coral wealth of our beleaguered planet are woefully inadequate and significantly under-resourced. The U.S. government has to take the initiative, make coral management a top priority, and establish more coral reef marine protected areas with no-take reserves. In June 1998, President Clinton signed the Coral Reef Protection Executive Order to preserve and protect U.S. coral reef ecosystems. However, the U.S has yet to develop a coordinated national strategy to protect and restore coral reef ecosystems from the effects of human activities and environmental stressors. Effective, long-term action on the part of the governments and intergovernmental bodies of the world must be based on high-quality scientific evidence and analysis, since coral systems are extremely fragile.
The decline in the quality and quantity of reef resources has serious consequences for tens of millions of dependent people, particularly those who fish on coral reefs. Beyond the economic dimension, however, the loss of coral reefs can have immeasurable environmental consequences for future generations.
Birkeland, Charles E. “Life and Death of Coral Reefs.” New York : Chapman & Hall, 1997
Crump, Andy. “Dictionary of Environment and Development: People, Places, Ideas, and Organizations.” Cambridge, MA : The MIT Press, 1993.
National Ocean Service. “Trends and Future Challenges for U.S. National Ocean and Coastal Policy.” Washington D.C : NOAA. August 1999.
Ravilious, Corinna; Spalding, Mark D. “World Atlas of Coral Reefs.” Berkeley, CA : University of California Press, 2001
Sumich, James L., Morrissey, John Francis. “Introduction to the Biology of Marine Life.”
Sudbury, MA : Jones and Bartlett Publishers, 2004