Coral reefs: Assessing the threat

Overview

Around the world, coral reefs are under assault from a multitude of sources. Depending on their location, reefs have been damaged directly through harmful practices such as coral mining, fishing with dynamite, or overfishing in general; haphazard coastal development; or even careless pleasure diving by tourists. Reefs have also suffered indirectly from sediment from inland deforestation and removal of coastal mangroves; from industrial pollution; and from nutrient pollution contributed by sewage, fertilizers, and urban runoff.

Just how much reefs have suffered from these depredations on a global basis is not yet clear. Both anecdotal and scientific reports of reef damage have increased over the past 20 years, and reef specialists agree there is a serious global decline [1]. In 1992, Australian reef ecologist Clive Wilkinson estimated that some 10 percent of the world’s reefs were already severely degraded; he predicted that figure would rise to 30 percent within the next two decades, with further losses continuing as populations in the coastal tropics surge [2] But these are just rough estimates, based on expert opinion. To date, no survey of reef conditions has been conducted worldwide, so scientists do not know the actual condition of the vast majority of the world’s reefs. In the Pacific, for example, 90 percent of coral reefs have yet to be assessed [3].

Although definitive data on reef conditions are some years off, a preliminary analysis of current reef threats indicates that a high percentage of the world’s coral reefs are at risk of degradation. The ongoing assessment, which is being conducted by the World Resources Institute, the International Centre for Living Marine Aquatic Resources, and the World Conservation Monitoring Centre, looks at four broad categories of potential threat to coral reefs: coastal development, overfishing and destructive fishing practices, land-based pollution (especially sediment) from deforestation and agriculture, and marine pollution from oil spills and the discharge of oily ballast water. The analysis, due to be published in June 1998, does not measure actual reef conditions but estimates the threat to reefs based on the proximity and intensity of known risk factors, such as ports, urban centers, coastal population density, and land use patterns [4]. (See More Than Half the World’s Reefs Are at Risk from Human Activities.)

Key findings include the following:

• Globally, 58 percent of the world’s reefs are at risk from human activities, with about 27 percent of reefs at high or very high risk.
• Significant regional differences exist regarding the degree of risk that coral reefs face. The reefs of Southeast Asia, which are the most species-diverse in the world, are also the most threatened, with more than 80 percent at risk, including 55 percent at high or very high risk. On the other hand, the reefs in the Pacific region, which contains more reef area than any other region, face comparatively less risk. Forty-one percent of Pacific reefs were classified as threatened, and just 10 percent face a high risk.

This ongoing assessment suggests that overexploitation (overfishing and destructive fishing practices) and coastal development pose the greatest potential threat to reefs, with each of these threats affecting about one third of all reefs [5]. (See Reef Threats Are Extensive.)

More Than Half of World Reefs Are at Risk fro Human Activities Coral Reef Area, by Region, Classified by Risk Category Source: Lauretta Burke et al., Reefs at Risk: A Map-Based Indicator of Potential Threats to The World’s Coral Reefs, (World Resources Institute, Washington, D.C., 1998). Note: Reefs classified as low risk are not considered in imminent danger.	Reef Threats Are Extensive Percentage of Reefs at Risk from Individual Threat Factors Source: Lauretta Burke et al., Reefs at Risk: A Map-Based Indicator of Potential Threats to The World’s Coral Reefs, (World Resources Institute, Washington, D.C., 1998).

References and notes

1. Stephen C. Jameson et al., State of the Reefs: Regional and Global Perspectives, Background Paper, Executive Secretariat, International Coral Reef Initiative (U.S. National Oceanic and Atmospheric Administration, Washington, D.C., 1995), p. 24.

2. Clive Wilkinson, “Coral Reefs of the World Are Facing Widespread Devastation: Can We Prevent This Through Sustainable Management Practices?,” in Proceedings of the 7th International Coral Reef Symposium, Vol. 1 (University of Guam, Guam, 1993), pp. 11-21.

3. Elizabeth Pennisi, “Brighter Prospects for the World’s Coral Reefs?,” Science, Vol. 277 (July 25, 1997), p. 492.

4. Lauretta Burke et al., Reefs at Risk: A Map-Based Indicator of Potential Threats to the World’s Coral Reefs, draft report (World Resources Institute, Washington, D.C., 1998), pp. 3-11.

5. Ibid., p. 2.