Percent of Reefs at Risk by Marine Ecoregion

Nov 15, 2011 (Last modified Jan 13, 2016)
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Percent of coral reefs at risk, by marine ecoregion.

The original Reefs at Risk indicator was devised by Bryant et al. (1998) with considerable expert consultation and utilized multiple global data layers to develop separate threat layers measuring coastal development, marine-based pollution, overexploitation and destructive fishing, and inland pollution and erosion. There are areas where particular elements of the model were not as effective, but it has proved a valuable generic tool that has led to further regional studies for Southeast Asia and for the Caribbean that followed the same basic principles, with only minor amendments to the model.

Bryant et al. (1998) used the combined threat layers to derive a simple three-point threat index (low, medium, or high) for each reef pixel (4 × 4 km). In the present map, we used these to generate the proportion of reefs threatened (medium or high threat) by ecoregion.

Although data were available for a few ecoregions in temperate ecoregions and in West Africa, these were deliberately excluded because these are not true coral reefs and the findings would be misleading. Being based on proportions, the map gives equal weighting to regions with very few reefs and those where reefs are dominant ecosystems. For example, around the Gulf of Aden and much of the Indian subcontinent, coral reefs are relatively rare habitats. These are indeed areas of grave concern, but the relatively low total area of reefs in these regions makes them a marginally lower point of concern than the extensive and diverse areas that are singled out in the text.

These data were derived by The Nature Conservancy, and were displayed in a map published in The Atlas of Global Conservation (Hoekstra et al., University of California Press, 2010). More information at

Data derived from:
Bryant, D., L. Burke, J. McManus, and M. Spalding. 1998. Reefs at Risk: A Map-Based Indicator of Threats to the World’s Coral Reefs. Washington, DC: World Resources Institute, International Center for Living Aquatic Resources Management, UNEP World Conservation Monitoring Centre and United Nations Environment Programme.
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The Nature Conservancy
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Hoekstra, J. M., J. L. Molnar, M. Jennings, C. Revenga, M. D. Spalding, T. M. Boucher, J. C. Robertson, T. J. Heibel, with K. Ellison. 2010. The Atlas of Global Conservation: Changes, Challenges, and Opportunities to Make a Difference. Ed. J. L. Molnar. Berkeley: University of California Press.

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