As published in the SeaWeb Ocean Update March 23, 2011, Vol. 16, No. 3A new, comprehensive analysis has found that local and global pressures are threatening 75 percent of the world's coral reefs. The analysis incorporates impacts from climate change, including warming seas and rising ocean acidification but concludes that local pressures-such as overfishing, coastal development, and pollution-pose the most immediate and direct risks.
"Reefs at Risk Revisited," published by the World Resources Institute (WRI) in conjunction with 30 other organizations, including SeaWeb, is an update of a 1998 WRI publication and takes advantage of the latest data and satellite information to map coral reefs to a resolution 64 times higher than the original report. It concludes that more than 60 percent of the world's reefs are under immediate and direct threat from one or more local sources-such as overfishing and destructive fishing, coastal development, watershed-based pollution, or marine-based pollution and damage. That figure rises to 75 percent when local threats are combined with thermal stress caused by rising ocean temperatures, which are linked to the widespread weakening and mortality of corals from mass coral bleaching.
The percent of reefs rated as threatened has increased by 30 percent in the more than 10 years since the first "Reefs at Risk" analysis, with increases being noted in all local threat categories and in all regions. The main cause of greater pressure on reefs since 1998 has been an 80 percent increase in the damage caused by overfishing and destructive fishing, most significantly in the Pacific and Indian Ocean regions, a change that is largely due to the growth in coastal populations living near reefs. Pressure on reefs from coastal development, watershed-based pollution, and marine-based pollution and damage has also increased dramatically from 1998 levels.
Pressures will increase as global threats continue to develop, the report says. The analysis projects that during the 2030s, roughly half of reefs globally will experience sufficient thermal stress to induce severe bleaching in most years. During the 2050s, this percentage is expected to grow to more than 95 percent. At the same time, rising levels of carbon dioxide in seawater are altering the chemistry, and increasing the acidity, of the ocean, reducing the saturation level of aragonite, a compound corals need to build their skeletons. By 2030, fewer than half the world's reefs are projected to be in areas where aragonite levels are ideal for coral growth, suggesting that coral growth rates could be dramatically reduced. By 2050, only about 15 percent of reefs will be in areas where aragonite levels are adequate for coral growth. The combined impacts of ocean warming and acidification will increase the threat levels on more than half of all reefs by 2030, pushing the percentage of threatened reefs to more than 90 percent by 2030.
Added to the problem, the report finds that just 27 percent of the world's reefs are located within marine protected areas (MPAs), and that this proportion drops to 16 percent for reefs outside Australia. Furthermore, given that quality of management varies from one MPA to another, the reports calculates that only 6 percent of the world's reefs are located in reefs that are managed effectively.
"Well-managed marine protected areas are one of the best tools to safeguard reefs," said Mark Spalding, senior marine scientist at The Nature Conservancy and a lead author of the report. Although local protective measures will not in themselves counter the impacts of global threats arising from climate change and ocean acidification, a growing body of evidence has shown that reducing local threats such as overfishing and nutrient and sediment pollution may allow reefs to recover more quickly from coral bleaching. Strategic planning to enhance local-scale reef resilience should target critical areas, building networks of protected areas that include and replicate different parts of the reef system as well as incorporate areas critical for future reef replenishment.
"Coral reefs are valuable resources for millions of people worldwide. Despite the dire situation for many reefs, there is reason for hope," said Lauretta Burke, senior associate at WRI and a lead author of the report. "Reefs are resilient, and by reducing the local pressures we can buy time as we find global solutions to preserve reefs for future generations."