Corals and the Threat of Global Climate Change

It now appears that corals are threatened by global climate change. These threats are outlined in a recent report by the World Wildlife Fund (WWF) entitled "Coral Reefs and Climate Change". According to an earlier report, "Reefs at Risk" (a joint publication of the United Nations Environment Programme (UNEP), Intergovernmental Oceanographic Commission (IOC), World Meteorological Organization (WMO) , International Union for the Conservation of Nature (IUCN), and WWF), global climate change is expected to lead to the following changes over the next century:

Photo courtesy of the National Oceanic and Atmospheric Administration (NOAA), International Year of the Reef, Reporter's Tip Sheet #17.

 

We may already be seeing the negative impact of increased sea surface temperatures on the health of corals. The most visible symptom of declining coral health is coral bleaching . Because many corals live in water which is already near their upper temperature limit, a water temperature increase of only a few degrees can be deadly. As water temperatures rise, corals become increasingly stressed. When stress levels get too high, corals expel the symbiotic algae, or zooxanthellae (tiny one-celled plants) which live within the thin layer of live coral tissue. Zooxanthellae are important because they turn sunlight into food for their coral hosts. They also facilitate the formation of the coral skeleton -- the main structural component of coral reefs. Because zooxanthellae give corals their various rich colors, a coral without zooxanthellae appears bleached. Corals can not thrive without zooxanthellae. For coral reefs that are already stressed due to poor water quality, destructive fishing, or frequent interactions with irresponsible divers and snorkellers, increased water temperatures could become the proverbial straw that breaks the camel's back.

Other Threats to Coral Reefs

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Coral Paleoclimatology website by Heather Benway, NOAA Office of Global Programs, hosted by the NOAA Paleoclimatology Program. Please contact us if you have any comments and/or suggestions.