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Coral Reefs
Related Links
IPCC Working
Group II, Fourth Assessment Report, Chapter 6, Coastal Systems and Low-Lying Areas, 2007 
[PDF, 43 pp., 1.94 MB, About PDF]
Coral reefs provide our oceans with the highest biodiversity of any marine ecosystem. Corals are formed from the skeletons of plants and animals that secrete limestone (calcium carbonate), and harbor more than 25 percent of all known ocean fish. Just as fish find refuge in the reefs, many marine organisms live inside the corals, adding up to nearly a million species of fish or other marine life that make up a coral reef ecosystem.
Coral reefs are also a significant food source for many coastal communities, and serve important functions as atoll island foundations, coastal protection structures, and sources of beach sand. They have economic value for recreation and tourism and support emerging opportunities in biotechnology.
Climate change is one cause of coral reef degradation. Many coral reefs are surviving at or close to their temperature tolerance levels, so rising sea surface temperatures are creating more hostile conditions for the corals. As temperatures rise, corals expel the colorful organisms that live inside them and appear “bleached.” Although these organisms re-colonize the corals once temperatures return to a more tolerable range, repeated or prolonged bleachings have proven to be fatal for some reefs, primarily due to the loss of nutrients that the organisms provide for the coral.
Atmospheric carbon dioxide (CO2) reacts with seawater to form carbonic acid, leading to increased acidity in the oceans. This higher acidity—or more accurately, reduced alkalinity, because the oceans are unlikely to ever become truly acidic—hampers the ability of corals to build their calcium carbonate skeletons, slowing or in some cases even halting their growth. More acidic waters may also weaken existing coral structures, leading to erosion of reefs (IPCC, 2007a, Kleypas et al., 2006).
Since the beginning of the Industrial Revolution, the ocean's surface has become more acidic—by about 0.1 pH unit—and since 1980 about one-third of all human emissions of CO2 have been stored in the oceans. The current rate of oceanic CO2 uptake far exceeds the rate at which nature can restore the system to normal conditions. Researchers project that over the next few centuries, ocean pH will decline faster and to a lower (more acidic) value than any experienced in the last several hundred million years (IPCC, 2007b , Kleypas et al., 2006).
A doubling of atmospheric CO2 concentrations above pre-industrial levels is expected to reduce calcium carbonate formation in some coral species by 20-60 percent, and many reefs could reach critical states by 2070 (IPCC, 2007a).
References
- IPCC, 2007a: Climate Change 2007: Impacts, Adaptation, and Vulnerability . Contribution of Working Group II to the Third Assessment Report of the
Intergovernmental
Panel on Climate Change [Parry, Martin L., Canziani, Osvaldo F., Palutikof, Jean P., van der Linden, Paul J., and Hanson, Clair E. (eds.)]. Cambridge University Press, Cambridge, United Kingdom, 1000 pp.
- IPCC, 2007b: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning (eds.)]
- Kleypas, J.A., R.A. Feely, V.J. Fabry, C. Langdon, C.L. Sabine, and L.L. Robbins, 2006. Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A Guide for Future Research , report of a workshop held 18-20 April 2005, St. Petersburg , FL , sponsored by NSF, NOAA, and the U.S. Geological Survey, 88 pp.