Overexploitation of reef resources has several effects. Destructive fishing practices, such as dynamite or cyanide fishing and trawling in deeper waters, cause direct physical damage to corals. The indirect effects of overfishing appear to be more widespread, although poorly understood by scientists. At a minimum, overfishing results in shifts in fish size and species composition within reef communities, which may precipitate large-scale ecosystem changes [6].
In parts of the Caribbean, this process appears to have led to major changes in reef composition, particularly near Jamaica. Widespread overfishing in the region over many decades has led to very low levels of herbivorous fish, which normally play an important part in keeping algae from overgrowing reefs. In the absence of herbivorous fish, the role of keeping algae levels in check fell to a species of grazing sea urchin. When an epidemic nearly wiped out the beneficial urchins on Jamaican reefs in the early 1980s, algae quickly overgrew and killed the corals. Subsequently, hurricanes in the region reduced the now largely dead reef framework to rubble, with the result that living corals that used to cover half of the seafloor in the shallow nearshore waters off Jamaica now only cover 5 percent of the bottom [7]. Some scientists claim this is a harbinger of events to come as reefs around the world continue to be overfished. Others argue that these major ecosystem effects may be reversible [8].
Coastal development also gives rise to several harmful effects. Direct effects come from coral mining, shoreline filling for land reclamation, and harbor dredging. Indirect effects, however, are more pervasive. Algal blooms resulting from nutrient-laden sewage released nearshore can block sunlight in the water column, stunting coral growth and interfering with reproduction. Shoreline construction disturbs sediments, which smother corals. Warm water discharges from power plants and industrial effluents also take their toll [9].
Even tourism, where it is unregulated, can pose a threat. For example, recreational divers in the Gulf of Aqaba, a finger of the Red Sea, have caused considerable coral destruction through trampling and the dropping of dive-boat anchors [10].
The prospect of widespread reef losses is particularly worrisome given the critical role they play in fostering the productivity of the tropical oceans. Coral reefs are often compared with tropical rainforests in terms of their importance as habitat and the biological diversity they harbor. Some 4,000 species of fish and 800 species of reef-building coral have been described to date, but the total number of species associated with reefs is probably more than 1 million [11] [12].
Reefs are also an integral part of the livelihood and food supply of the human populations that live near them. It has been estimated that about one quarter of the potential fish harvests in developing countries come from coral reefs [13]. Properly managed, reefs can yield, on average, 15 tons of fish and other seafood per square kilometer each year [14]. Reefs yield tourist dollars as well. Caribbean countries, which attract millions of visitors annually to their beaches and reefs, derive one half of their gross national product (GNP) from the tourism industry, valued at US$8.9 billion in 1990 [15]. Reefs also provide essential services like coastal protection, buffering adjacent shorelines from erosive wave action and storm impacts.
Because reefs provide so many benefits, degrading them is costly. A recent study found that the costs of destroying just 1 kilometer of reef range from about US$137,000 to almost US$1.2 million over a 25-year period, just counting the economic value of fisheries, tourism, and shoreline protection [16].
The realization that reefs and their many benefits are increasingly in jeopardy has begun to prompt action at many levels. The International Coral Reef Initiative (ICRI), started in 1995, stresses the need for integrated coastal management to minimize the detrimental effects of coastal development. The ICRI now boasts the participation of more than 80 nations and includes a major effort to monitor global reef conditions (the International Coral Reef Monitoring Network) – an essential component of any effort to manage reef impacts [17].
At the national and local levels, a number of governments and communities have taken steps to protect and restore coral reefs. In general, these examples of good stewardship involve a combination of planning, management, law enforcement, environmental education, and legal protection. Approaches range from building sewage and industrial waste treatment facilities, to regulating access and use of reefs (for example, by establishing community ownership over reef fisheries), to restricting development in sensitive coastal areas [18].
Australia’s Great Barrier Reef, the largest reef in the world, illustrates the potential of careful reef management. The reef remains in good condition, although sedimentation from runoff is a threat in some localized areas. Careful zoning of the reef – 20 percent is protected, the rest is managed for multiple use—along with strict enforcement and environmental education has preserved this globally important resource [19].
References and notes
6. Op. cit. 4, p. 9.
7. Terrence P. Hughes, “Catastrophes, Phase Shifts, and Large- Scale Degradation of a Caribbean Coral Reef,” Science, Vol. 265 (September 9, 1994), p. 1547.
8. Op. cit. 3, pp. 491-493.
9. Robert H. Richmond, “Coral Reef Resources: Pollution’s Impacts,” Forum for Applied Research and Public Policy (Spring 1994), p. 55.
10. Global Environment Facility, “The Hashemite Kingdom of Jordan: Gulf of Aqaba Environmental Action Plan,” Project Document No. 15290JO, Global Environment Division, Environment Department (The World Bank, Washington, D.C., 1996), p. 3.
11. Gustav Paualy, “Diversity and Distribution of Reef Organisms,” in Life and Death of Coral Reefs, Charles Birkeland, ed. (Chapman and Hall, New York, 1997), pp. 302-304.
12. David Malakoff, “Extinction on the High Seas,” Science, Vol. 277 (July 25, 1997), p. 487.
13. Op. cit. 1, p. 24.
14. Herman Cesar, Economic Analysis of Indonesian Coral Reefs, (The World Bank, Washington, D.C., 1996), p. 16.
15. Op. cit. 1, p. 24.
16. Charles Barber and Vaughan R. Pratt, Sullied Seas: Strategies for Combating Cyanide Fishing in Southeast Asia and Beyond (World Resources Institute and International Marine Life Alliance, Washington, D.C., and Manila, 1997), p. 4.
17. Clive Wilkinson, Coordinator, Global Coral Reef Monitoring Network, Townsville MC, Australia, December 1997 (personal communication).
18. Op. cit. 4, p. 23.
19. Op. cit. 4, p. 25.
