Key Facts

Elliott Key in Florida's Biscayne National Park is formed from an ancient coral reef. Living corals at the heart of the unique marine ecosystem of the Florida Keys are vulnerable to rising water temperatures, ocean acidification, and other effects of climate change.

• Even small increases in water temperature can cause coral bleaching, and if such stress continues, corals can die.^3,10,14
• The intensity and frequency of coral bleaching has increased significantly over the past 30 years, causing death or severe damage to one-third of the world's corals.^3,10
• If our carbon emissions continue to rise at current rates, scientists project that waters around the Florida Keys are likely to become too warm and too acidic to support coral reefs.^3,17,18

Details

The Florida Keys are the exposed portions of an ancient limestone or an old coral reef that forms a chain of islands extending from the tip of the Florida peninsula to Key West. Biscayne National Park encompasses the northernmost Florida Keys, including Elliott Key, and the beginning of the world's third-largest coral reef.²

Corals are marine animals. Their spectacular coloration comes from symbiotic algae, which also nourish them. Coral reefs provide food and habitat for other species, including a wide range of fish, and protect coastlines from large waves.³ Reefs such as the one in Biscayne National Park—visited by more than 400,000 people in 2009—also support tourism.⁴ More than 100 million people worldwide are directly economically dependent on coral reefs, according to estimates.⁶

Coral reefs are threatened by rising water temperatures, ocean acidification, and sea-level rise.^3,5 Coral reefs typically live within a specific range of temperature, light, and concentration of carbonate in seawater.⁶ When increases in ocean temperature or ultraviolet light stress the corals, they lose their colorful algae, leaving only transparent coral tissue covering their white calcium-carbonate skeletons.⁶ This phenomenon is called coral bleaching.

Even small increases in water temperature can cause coral bleaching. If such stress continues, the corals can die.^3,7 As corals die off, the number of marine species supported by the reef declines, and local extinctions can occur.^3,8

Since 1950, global mean sea surface temperatures have risen roughly 1o F (0.6o C).⁹ The intensity and frequency of coral bleaching have increased significantly during the past 30 years, causing death or severe damage to one-third of the world's corals. Corals are also becoming more diseased.^3,10 In 2005, a record-breaking hot year globally, the Florida Keys experienced bleaching in summer followed by disease in September.^3,10

Ocean acidification poses an added danger to corals and other sea animals that need calcium carbonate to build shells or skeletons.^3,11,12 As concentrations of carbon dioxide in Earth's atmosphere rise, the oceans absorb carbon dioxide and become more acidic. Ocean acidification means that less calcium carbonate is available for sea life such as corals to build their reefs.^3,13

What the Future Holds

Unless we make deep and swift cuts in our heat-trapping emissions, scientists project that corals risk ultimately being unable to build shells or skeletons as the oceans become so sour that the mineral comprising the reefs begins to dissolve.^3,10,14

Studies show that a doubling of atmospheric carbon dioxide is likely to reduce coral calcification more than 30 percent. And reefs are eroding faster than new corals can form, even at lower concentrations of CO2.^3,15 If corals do not have healthy reproduction or growth rates, they may be unable to build and keep pace with sea-level rise.⁶ In that case, scientists expect the Florida Keys, Puerto Rico, Hawaii, and the Pacific Islands risk losing their reefs.^3,16

Coral skeletons are composed of aragonite, or calcium carbonate in its crystalline form. If our carbon emissions—and ocean acidity—continue to rise at current rates, aragonite in the southern ocean could start to dissolve by 2060. Marine organisms that build their shells out of calcite, in contrast, might not begin dissolving until the end of the century.¹²

Scientists say that the waters around the Florida Keys are eventually unlikely to support coral reefs because of declining levels of carbonate in surface waters.^3,17,18 With snorkeling and scuba diving at risk, the future of tourism in Biscayne National Park is uncertain.

Credits

Endnotes

1. Photograph courtesy of John Brooks, National Park Service. ↑
2. National Park Service. Biscayne National Park: natural features and ecosystems. Online at http://www.nps.gov/ bisc/ naturescience/ naturalfeaturesandecosystems.htm. Accessed April 26, 2010. ↑
3. U.S. Global Change Research Program. 2009. Global climate change impacts in the United States. Edited by T.R. Karl, J.M. Melillo, and T.C. Peterson. Cambridge University Press. ↑
4. National Park Service. 2009. Ranking report for recreation visits. Online at http://www.nature.nps.gov/ stats/ viewReport.cfm. Accessed April 25, 2010. ↑
5. Frumhoff, P.C., J.J. McCarthy, J.M. Melillo, S.C. Moser, and D.J. Wuebbles. 2007. Confronting climate change in the U.S. Northeast: Science, impacts, and solutions. Synthesis report of the Northeast Climate Impacts Assessment. Cambridge, MA: Union of Concerned Scientists. ↑
6. Hoegh-Guldberg, O. 2005. Low coral cover in a high-CO2 world. Journal of Geophysical Research 110 (doi:10.1029/2004JC002528). ↑
7. Donner, S.D., W.J. Skirving, C.M. Little, M. Oppenheimer, and O. Hoegh-Guldberg. 2005. Global assessment of coral bleaching and required rates of adaptation under climate change. Global Change Biology 11(12):2251-2265. ↑
8. Graham, N.A.J., S.K. Wilson, S. Jennings, N.V.C. Polunin, J.P. Bijoux, and J. Robinson. 2006. Dynamic fragility of oceanic coral reef ecosystems. Proceedings of the National Academy of Sciences 103(22):8425-8429. ↑
9. Bindoff, N., J. Willebrand, V. Artale, A. Cazenave, J. Gregory, S. Gulev, K. Hanawa, C. LeQuéré, and co-authors. 2007. Observations: Oceanic climate change and sea level. In: Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H. L. Miller. Cambridge University Press, pp. 385-432. ↑
10. Janetos, A., L. Hansen, D. Inouye, B.P. Kelly, L. Meyerson, B. Peterson, and R. Shaw. 2008. Biodiversity. In: The effects of climate change on agriculture, land resources, water resources, and biodiversity in the United States. Edited by P. Backlund, A. Janetos, D. Schimel, J. Hatfield, K. Boote, P. Fay, L. Hahn, C. Izaurralde, B.A. Kimball, T. Mader, J. Morgan, D. Ort, W. Polley, A. Thomson, D. Wolfe, M.G. Ryan, S.R. Archer, R. Birdsey, C. Dahm, L. Heath, J. Hicke, D. Hollinger, T. Huxman, G. Okin, R. Oren, J. Randerson, W. Schlesinger, D. Lettenmaier, D. Major, L. Poff, S. Running, L. Hansen, D. Inouye, B.P. Kelly, L. Meyerson, B. Peterson, and R. Shaw. Synthesis and assessment product 4.3. Washington, DC: U.S. Department of Agriculture, pp. 151-181. ↑
11. Clarke, L., J. Edmonds, H. Jacoby, H. Pitcher, J. Reilly, and R. Richels. 2007. Scenarios of greenhouse gas emissions and atmospheric concentrations. Sub-report 2.1A of synthesis and assessment product 2.1. Washington, DC: Office of Biological and Environmental Research, U.S. Department of Energy. ↑
12. Orr, J.C., V.J. Fabry, O. Aumont, L. Bopp, S.C. Doney, R.A. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R.M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R.G. Najjar, G.-K. Plattner, K.B. Rodgers, C.L. Sabine, J.L. Sarmiento, R. Schlitzer, R.D. Slater, I.J. Totterdell, M.-F. Weirig, Y. Yamanaka, and A. Yool. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437(7059):681-686. ↑
13. Monaco declaration. 2009. Developed at the Second International Symposium on the Ocean in a High-CO2 World, Monaco, October 2008. Online at http://ioc3.unesco.org/ oanet/ Symposium2008/ MonacoDeclaration.pdf. ↑
14. Feely, R.A., C.L. Sabine, J.M. Hernandez-Ayon, D. Ianson, and B. Hales. 2008. Evidence for upwelling of corrosive "acidified" water onto the continental shelf. Science 320(5882):1490-1492. ↑
15. Royal Society. 2005. Ocean acidification due to increasing atmospheric carbon dioxide. Policy document 12/05. London: Royal Society. ↑
16. Carpenter, K.E., M. Abrar, G. Aeby, R.B. Aronson, S. Banks, A. Bruckner, A. Chiriboga, J. Cortés, J.C. Delbeek, L. DeVantier, G.J. Edgar, A.J. Edwards, D. Fenner, H.M. Guzmán, B.W. Hoeksema, G. Hodgson, O. Johan, W.Y. Licuanan, S.R. Livingstone, E.R. Lovell, J.A. Moore, D.O. Obura, D. Ochavillo, B.A. Polidoro, W.F. Precht, M.C. Quibilan, C. Reboton, Z.T. Richards, A.D. Rogers, J. Sanciangco, A. Sheppard, C. Sheppard, J. Smith, S. Stuart, E. Turak, J.E.N. Veron, C. Wallace, E. Weil, and E. Wood. 2008. One-third of reef-building corals face elevated extinction risk from climate change and local impacts. Science 321(5888):560-563. ↑
17. National Assessment Synthesis Team. 2001. Climate change impacts on the United States: The potential consequences of climate variability and change. Cambridge University Press. Online at http://www.usgcrp.gov/ usgcrp/ Library/ nationalassessment/. ↑
18. The high-emissions scenario referred to here is the path known as A1FI from the Intergovernmental Panel on Climate Change. ↑