Coral Bleaching

Coral bleaching occurs when the densities of zooxanthellae decline in response to a stress (Kleppel et al. 1989). When corals bleach they commonly lose 60-90% of their zooxanthellae and each zooxanthella may lose 50-80% of its photosynthetic pigments (Glynn 1996). If the stress is removed then the zooxanthellae will be regained; bringing the colour back to the coral. However if the stress is prolonged then the coral host will die.

Coral bleaching in the Great Barrier Reef (Photo by Ray Burkelmans - AIMS, 2006.).

The main anthropogenic stress that causes bleaching is temperature change. This can occur naturally by seasonal variation and El Niño (Brown et al., 1995.) or by anthropogenic influences such as global warming (Hoegh-Guldberg, 1999.). Other stresses include UV irradiation (Brown et al., 1994), bacterial infection (Kushmaro et al., 1996), and lowered salinity and pollution (Glynn, 1993).

Most of the recent scientific literature suggests that global warming has increased mass coral bleaching on a global scale in the last few decades (Hoegh-Guldberg, 1999.). In order to reduce CFC’s (the main cause of global warming) the United Nations Framework Convention on Climate Change (UNFCCC) was put in place. This included 180 countries willing to reduce their CFC emissions (UNFCCC, 2006.). To prevent other anthropogenic influences to coral bleaching, Chapter 17, of Agenda 21 was put in place by the UN (Dight, & Scherl, 1997.).