Nearly one-fifth of the world’s coral reefs have already succumbed to the combined onslaught of global warming, water pollution, and overfishing. Without immediate measures to mitigate climate change and reduce the local pressures on reefs, the world is set to lose another 15% of coral reefs over the next 10−20 years and 20% over 20−40 years. Those are the main conclusions of a new report, produced jointly by a handful of government agencies and nongovernmental organizations from around the world, including the U.S. National Oceanic and Atmospheric Administration (NOAA).
Nearly one-fifth of the world’s coral reefs have already succumbed to the combined onslaught of global warming, water pollution, and overfishing. Without immediate measures to mitigate climate change and reduce the local pressures on reefs, the world is set to lose another 15% of coral reefs over the next 10−20 years and 20% over 20−40 years. Those are the main conclusions of a new report, produced jointly by a handful of government agencies and nongovernmental organizations from around the world, including the U.S. National Oceanic and Atmospheric Administration (NOAA).
The report brings some “sobering news,†said Clive Wilkinson, the report’s editor, as he introduced the study at a reception held at the National Aquarium in Washington, D.C., on December 9, 2008. “It is clear that human activities continue to degrade coral reefs.â€
However, not all coral reefs are doomed. The 372 coral reef scientists and managers from 96 countries who contributed to the report also conclude that 46% of the world’s coral reefs are beyond the reach of most threats, with the exception of climate change.
This past year, 2008, was the International Year of the Reef. The review is the latest in a series of scientific papers and agency reports that have documented the sad plight of corals in the past year. For nearly four decades, scientists have been documenting the health of corals. The recent flurry of studies is the result of collaborations among scientists, environmental advocates, and natural resource managers attempting to understand the issue on a global scale.
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An ecosystem fending off many blows
Climate change is threatening the survival of terrestrial and marine ecosystems alike. Like the bacteria we harbor in our guts, reef-building corals host certain microscopic algae in their bodies. The algae provide food to the corals, while the corals give the algae safe habitat. But, when waters become warmer, the algae lose some of their green pigments, and/or the heat-stressed corals rid themselves of the algae. The result: corals bleach, starve, and, in extreme cases, die off.
One of the best-known coral-bleaching events attributed to warmer sea surface temperatures happened in 2005, when reefs in large swaths of the Eastern Caribbean and tropical Atlantic bleached. In a paper published last year in the Proceedings of the National Academy of Sciences U.S.A., marine biologist Simon Donner of the University of British Columbia (Canada) and his colleagues used computer models to illustrate that the unusually warm summer of 2005 that caused the bleaching was unlikely to have been from natural climatic variations.
Increasing CO2 in the air also leads to more CO2 in the oceans. In water, the greenhouse gas reacts with water molecules to form carbonic acid. Too much acid wreaks havoc on marine life. The calcium carbonate in coral reefs, as well as in the shells of many marine animals, can dissolve in acidic waters. In another report on ocean acidification, released in November 2008, scientists at the environmental advocacy group Oceana predict widespread population crashes in marine ecosystems, including coral reefs, if we fail to reduce our carbon emissions over the next few decades.
“Somewhere around 480−500 parts per million [ppm] CO2 and about two degrees [Celsius] sea temperature rise is about all that reefs can handle,†notes Mark Eakin, coordinator of NOAA’s Coral Reef Watch. The current atmospheric concentration of CO2 is about 380 ppm. Eakin is referring to results from a 2007 paper that he and his colleagues published in Science. “Now, it doesn’t mean that they will instantly all keel over at that point,†he adds. Rather, it implies that if those thresholds are crossed, the reefs will be unable to deal with additional stressors such as sediment pollution and overfishing, he explains.
Nutrient and sediment pollution, toxic chemicals in water bodies, overfishing, and illegal fishing are the local and regional threats to the survival of coral reefs. The multiple blows from the local and global stressors are weakening these vibrant marine ecosystems, reducing their ability to survive in their rapidly changing environment.
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