A Guide To Protecting Coral Reefs

By Rodney M. Fujita and Mark S. Epstein, Environmental Defense Fund;
Thomas J. Goreau, Global Coral Reef Alliance;
Kristina Gjerde, Environmental Solutions International

Originally published November 1992

Coral reef ecosystems deserve special attention within the scope of global efforts to protect our natural heritage. They play an important role in sustaining biological diversity, global biogeochemical cycles, and the economies of many countries. Despite these values, many coral reefs around the world are being rapidly degraded.

While the biological and economic importance of coral reefs is fairly well documented, scant attention has been paid to them by policy makers at any level of political organization until recently. The degradation and destruction of coral reefs have such varied sources and widespread environmental and economic impacts, and funding for conservation is so limited, that coral reef protection must be addressed not only at the local, but at the regional and global levels as well.

Local threats to coral reefs, such as sewage pollution, overfishing, and deforestation, must be addressed primarily by countries containing coral reefs, supplemented when appropriate by international financial and technical assistance. Regional problems, such as the transport of water and air pollution across national boundaries, must be addressed through regional legal instruments, again with international assistance to implement regional policies. Finally, the threats posed to coral reefs by global warming, ozone depletion, and international trade in coral reef organisms and natural products can only be reduced through international accords.

Indeed, truly comprehensive environmental protection must include long term environmental monitoring, integrated coastal management, effective marine sanctuaries, appropriate technologies for pollution prevention, and environmentally sensitive ways to utilize reef resources. These can only be implemented with substantial international economic and technical assistance. Thus, measures to ensure international assistance and cooperation in ameliorating the many threats to coral reefs must be included in all pertinent international agreements. The Framework Convention on Climate Change, the Convention on Biological Diversity, and Agenda 21, which were negotiated during the United Nations Conference on Environment and Development and signed in Rio de Janeiro, address this to some degree. However, firm commitments to alleviate environmental threats and implement environmentally sensitive development with new enforceable policies and funding are lacking.

To enable the reader to understand the requirements for coral reef ecological integrity, this paper first provides a brief overview of the structure and function of coral reef ecosystems and their interrelationships with other ecosystems. It next describes some of the many direct and indirect benefits humankind currently (and may in the future) reaps from reef ecosystems, and the anthropogenic stresses that are undermining many reef ecosystems. This section also describes domestic and international measures needed to protect coral reefs and provide a framework for environmentally sensitive development.

Coral reefs are among the ocean's most complex, biologically diverse, and beautiful marine ecosystems. They occur around the world in shallow (less than 100 m depth), clear tropical waters. Their range is restricted to between 30 ° N and 30 ° S of the equator Coral reefs occupy approximately 600,000 sq. km, or only about 0.2% of the ocean's surface. Some coral reefs, such as the Great Barrier Reef of Australia, the Barrier Reef of Belize, and the Florida Reef Tract of the United States of America, are enormous and stretch over hundreds of kilometers. One hundred and nine countries have coral reefs in their waters.

Massive reef structures are built over thousands of years by tiny coral polyps aided by minute dinoflagellate algae (zooxanthellae) that live in their tissues, calcifying algae, and other organisms that secrete calcium carbonate and adhesives. The production of calcium carbonate, or limestone, is called calcification. The complex, rock-like reef framework provides a living sheltering place and feeding ground for the multitudes of organisms that inhabit the reef. The process of reef formation is heavily dependent upon photosynthesis by reef-building organisms; hence, phytoplankton blooms, sediment and other factors that decrease the amount of light available to corals and calcifying algae are inimical to reef growth.

Because of their high rates of calcification, coral reefs play a major role in the global calcium cycle despite their limited areal extent, fixing about half of all the calcium entering the sea into calcium carbonate. Their role in the earth's carbon cycle and other geochemical cycles is presently under investigation. Models and limited field data indicate that coral reefs, counter-intuitively, appear to be very small net sources of carbon dioxide (less than 0.1 billion tons of carbon per year, as compared to about 6 billion tons of carbon annually from fossil fuel combustion) to the atmosphere on decadal time scales. This is due to the release of carbon dioxide during calcification, which involves the precipitation of calcium carbonate from bicarbonate and calcium in seawater. In addition, while coral reefs absorb large amounts of carbon dioxide (per unit area) during photosynthesis, they generally release almost equivalent amounts via respiration, resulting in little net storage.

Calcification by corals make reefs among the best recorders of marine environmental conditions such as sea level, siltation, and temperature over a variety of time scales, ranging from one year to thousands of years. Growth rate and environmental conditions are recorded in daily and annual growth bands, elemental ratios, and isotopic signatures, offering high resolution historical records. These records can be used to infer past sea levels, growing conditions, the effects of environmental management, and other important phenomena.

Coral reefs in general achieve high rates of gross productivity; i.e., they rapidly convert carbon and nutrients into food through photosynthesis. This is due in part to the many ways in which they capture and recycle nutrients from the environment, providing the symbiosis (biological partnership) between coral polyps and algae with sufficient nutrients to grow rapidly. Some reef organisms transform biologically unavailable atmospheric nitrogen gas into a form useful for coral and plant growth. Reefs capture nutrients from the sea and from groundwater, storing them in the myriad organisms living on reefs and sediments and recycling them tightly within and between these organisms.

Coral reefs often occur near land, and exchange energy and materials (e.g., nutrients and carbon) with mangrove forests and seagrass meadows. The health of coral reefs is affected by the quality of surface waters, groundwater, and air for miles around. Pollutants migrate in coastal currents, air flow patterns, rivers, and underground aquifers. Activities throughout the airshed and watershed, including those which destroy or degrade mangrove forests and seagrass meadows, further threaten the integrity of reefs. Coastal forests retain soil and capture nutrients originating from natural processes, atmospheric deposition (due to fossil fuel combustion and animal husbandry), domestic wastewater, and agricultural fertilizer applications. These forests also regulate fresh water flows into coastal waters, reducing their volume through evapotranspiration and discharging freshwater over long time periods, moderating sudden changes in salinity that are harmful to coral reefs and perhaps seagrasses. Closer to the coast, mangrove forests retain sediments, transform nutrients into organic matter, and harbor diverse and productive forms of life.

Seagrass meadows, often occurring in nearshore waters containing coral reefs and mangroves, retain fine sediments and provide food for many of the fishes and invertebrates that shelter in coral reefs; these organisms transport energy and materials between coral reefs and seagrass meadows. Seagrasses and mangroves also export dissolved organic materials and provide shelter and nursery grounds for myriad organisms that move between the three marine habitats, enriching coral reef productivity. Coral reefs dissipate wave energy, allowing mangroves and seagrass meadows to flourish. Reefs also produce calcareous sediment which provides substrate for seagrasses and mangroves to grow.

Reef development requires a minimum average temperature of about 20° C. Lethal maximum temperatures for corals range from 30 to 35° C, depending on location and species. Low salinities (less than 25-30 %) and high salinities (50-70 %) also limit reef development. The relatively narrow physiological limits of reef-building corals and other reef organisms make coral reefs sensitive to changes in environmental conditions induced by climate change, disturbance of watersheds, pollution, and other factors. Temperature is affected by water circulation, light levels, and regional temperature trends. Therefore, changes associated with global warming (shifts in circulation patterns, increased air temperature, changes in cloudiness, etc.) would be expected to have major impacts on coral reef ecology.

While coral reefs are sensitive to environmental changes, they appear to be able to recover effectively from physical disturbance or temporary pollution events provided that water quality is generally high. For example, the corals in Kaneohe Bay, Hawaii, for the most part recovered from severe overgrowth by algae after sewage inputs were diverted away from the Bay. However, community composition has not returned to conditions observed prior to sewage input due to the long lives of some key organisms, the lingering effects of nutrients and organic matter stored in sediments, and remaining nonpoint pollution. Damaged coral populations in Broward County, Florida (USA) recovered after water conservation efforts resulted in the abatement of the discharge of water draining the Everglades. Many reefs are buffeted by hurricanes, volcanoes, and other natural disturbances periodically, yet recover their high productivity and biological diversity. However, reefs that live in polluted water appear not to recover well from physical damage; coral growth is inhibited by algal blooms and other factors, and the settlement of new corals may be inhibited by encrusting organisms that thrive on sewage. This appears to be the case in some parts of the Florida Reef Tract and the Great Barrier Reef.

Since coral reefs depend on photosynthesis for survival, relatively clear water is needed for optimal coral reef development. Waters in and around coral reefs are characteristically very low in nutrients such as nitrogen and phosphorus. Low nutrient conditions are needed to prevent the excessive growth and accumulation of phytoplankton and seaweeds. Phytoplankton blooms resulting from excessive nutrient inputs decrease the light available for coral growth. Seaweed populations stimulated by excessive nutrient levels tend to overgrow corals and other organisms on reefs. Nutrients are delivered by ground and surface water loadings, atmospheric deposition, migrations of organisms, nitrogen fixation, upwelling, and horizontal advection.

Diverse and abundant populations of grazing fish (such as blue tangs) and invertebrates (such as sea urchins) are also required to prevent algae (seaweed and phytoplankton) from accumulating. Excessive seaweed growth is known to decrease coral vitality and diversity. Natural predators of grazers help keep their numbers within sustainable limits. Selective removal of grazers through fishing or disease probably exacerbates or causes blooms of algae. Innumerable intricate relationships exist between coral reef organisms, some of which are no doubt crucial to the viability of the ecosystem; however, few have been elucidated. Excessive harvest of species or large reductions in populations by any mechanism may therefore threaten the ecological integrity of coral reefs in currently unknown ways.

The reef's framework of coral and algae is ideal habitat for fish, lobsters, crabs and many other invertebrates. Hawksbill turtles and dolphins frequent nearby waters; conch, dugongs, rays, turtles, and other species find both feeding grounds and habitat in surrounding sand flats and seagrass meadows.

The extraordinary biological diversity of reefs makes them biologically important. Like rainforests, reefs have provided valuable scientific insights into the nature of symbiosis, ecological competition, evolution, and animal behavior. The numerous species residing and depending on coral reefs represent a bank containing the genetic diversity necessary for adaptation to changes in the environment, both anthropogenic and natural. While most corals and large reef organisms have been described, the taxonomy of some is uncertain and many other organisms have yet to be described.

A few principles governing patterns of diversity have emerged, however. Large reefs tend to be more diverse than small, isolated reefs. The most diverse reefs occur in seas north of Australia, such as the Java Sea, the waters of Indonesia, Papua New Guinea, the Phillipines, and the South China Sea. Although many coral reef species appear to be widely distributed, some have restricted ranges. These species would be especially vulnerable to local extirpation or extinction. For example, a newly discovered species of fire coral apparently restricted to the Gulf of Chiriqui, Panama, probably became extinct as a result of prolonged high temperatures during the 1982-1983 E1 Nino event. Two other fire coral species in the area suffered extreme reductions in range. A species of Acropora coral may have been extirpated from the eastern Pacific, and a Tubastraea species may have become extinct as well. The taxonomy of some coral reef organisms is in a state of flux; corals, sponges, and other species exhibit a great deal of variation of form and color with environmental variation. An adequate understanding of the degree of endemism, the range of species, the number of species, and thus the risks of extirpation and extinction in coral reefs will require further research.

Title: "A Guide to Protecting Coral Reefs"
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