Coral reefs under threat.

About one-fifth of the world's coral reefs have already been lost or severely damaged, while another 35 percent could be lost within 10-40 years, according to the latest review by the Global Coral Reef Monitoring Network. The number of coral reefs considered at low risk stood at 46 percent, up from' 30 percent only four years ago, but the number of effectively lost reefs remained constant during the period--although this figure was double the 10 percent lost or severely damaged in the first global estimate in 1992. However, the recent estimates do not take into account risks from climate change; when these are included, all coral reefs are in danger and widespread mortality is predicted.

Coral reefs in Asia and the Indian Ocean are most at risk, with 54 percent either lost or critically threatened and another 25 percent moderately threatened. Southeast Asia, which contains the highest biodiversity of all coral reefs as well some of the world's highest human population densities, has already lost 40 percent of its reefs (36,680 square kilometers).

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In the Caribbean region, 38 percent of coral reefs are either lost or critically threatened and 24 percent are moderately threatened. The Middle East region contains one of the areas with the lowest-risk reefs (in the Red Sea), as well as the area with the largest percentage of lost reefs, the Persian Gulf, Arabian Sea, and Gulf of Oman.

Coral reefs in the Pacific Ocean are by far in the best shape, with only 11 percent lost or critically threatened, 16 percent moderately threatened, and 72 percent considered at low risk.

There are roughly 284,000 square kilometers of coral reefs in the world, covering less than 0.1 percent of the world's oceans--equal to about 0.6 percent of the world's agricultural lands. But, though relatively rare, coral reefs support more than a quarter of all known fish species and more species per unit area than any other ecosystem. Coral reefs directly supply about 2-5 percent of the global fisheries harvest and are an important protein and income source, especially in developing countries. They provide resources and food for about 500 million people across the globe, including 30 million people who are almost completely dependent on reefs and associated coral resources. The associated goods and services are worth an estimated US$30 billion per year.

Many of the ongoing threats to coral reefs can be linked to human activities, including overfishing and destructive fishing practices such as using explosives and cyanide poison. Another threat is coastal development, which leads to lower water quality, increased sedimentation, and more pollution. These threats are expected to worsen: At least 39 percent of the world lives within 100 kilometers of an ocean, and projections indicate that population density will continue to grow in these coastal areas.

Climate change is arguably the most important factor for the future of coral reefs. Coral reefs are particularly susceptible to warming sea-surface temperatures, which over the last few decades have raised the frequency and intensity of coral bleaching events that can reduce coral growth and reproductive capacity, change reef fish species composition, and make the reefs vulnerable to disease and mortality. In 1998 (the second warmest year on record), the largest documented bleaching event killed 16 percent of the world's corals.

Another worrying climate change factor for coral reefs is increasing ocean acidity due to higher atmospheric carbon dioxide concentrations, which can decrease coral calcification and growth and lead to weaker structures and slowed reproduction. Ocean acidity has already increased by 30 percent.

Most approaches to coral reef protection rely on some degree of improved management. For example, socioeconomic modeling looks at how local peoples perceive threats to coral reefs as a way to help inform local management approaches. A revision to the monumental Reefs at Risk survey coordinated by the World Resources Institute is under way--relying on improved modeling and data and looking specifically at climate change threats--to offer a new look at coral reef threats that can be used in management decisions.

Vital Signs are adapted from Vital Signs Online, which contain additional data and more in-depth analyses.

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