Climate Change

Monday, August 14, 2006

CORAL REEF BLEACHING

Coral reefs are one of the most industrious and sensitive ecosystems on Earth. They provide services in form of fisheries, shoreline protection, tourism and they have assisted us with medicine (Union of Concerned Scientists 2005, Bureau of Oceans and International Environmental and Scientific Affairs 1999). As global temperatures are expected to increase and already it is, enormous pressure is exerted on reefs as a slight increase of temperature can cause coral to lose their symbiotic algae. Corals develop effectively where the water is between 26° and 30°C (Merle 2006). Above 30°C pending on species or ecotype, corals become separated from the symbiotic algae which are the crucial partners of their survival (Buddemeier and Fautin 1993). These algae are responsible for the feeding and colour of corals. When the algae die, corals turn whitish and are said to be “bleached”. According to Buddemeier and Fautin (1993) bleaching appears to be a basic physiological attribute of many, if not all, organisms having zooxanthellae, both in response to stress and in the absence of stress. Keep in mind that this is a natural occurring event.
Since the 1970 and 1980, a strong correlation existed between the increase water temperature and coral bleaching. These data were based on the El Nino that raised the water temperature of the Pacific near Tahiti resulting in over 500 kilometres of reefs that have been bleached. Similar results were observed for the reefs near the Caribbean Islands but on a lesser scale. During the mentioned above years the El Nino-effect raised the sea surface temperature with 4°C above normal, but global warming pose are far greater problem, as the El Nino occurs approximately every ten years, while global warming will kind of give a permanent increase of temperature (Union of Concerned Scientists 2005). Thus it is possible to associate coral bleaching to increase sea surface temperature due to global warming caused by anthropogenic activities.

Global warming will provide coral reefs with plenty of stress. Apart from the increase of temperature on the surface of the sea, humans will always increase their resources due to the ever increasing human population.
Thus mass bleaching events will become more frequent and widespread. Increasing human stresses such as pollution, overfishing, soil erosion, and physical damage from boats and other recreational activities will also weaken corals (Union of Concerned Scientists 2005, Bureau of Oceans and International Environmental and Scientific Affairs 1999). The time for coral to regenerate take several decades and the stresses mention above, will slow down their adaptation to the most important change, that of climate change.

Coral bleaching is not just an isolated case, but it is happening all over the ocean within the suitable climatic regions (tropical, warm temperatures), and several coral reefs in 60 countries in the Pacific Ocean, Indian Ocean, Red Sea, Persian Gulf, Mediterranean and Caribbean have been reported. It is appearing not only at shallow depth but also deeper down (Union of Concerned Scientists 2005).
Furthermore, as ocean warming coincides with sea-level rise and perhaps more frequent tropical storms and El Ninos, reefs are likely to experience greater coastal erosion, sedimentation, and turbidity, which would add to their demise.

Reference:

Union of Concerned Scientists. Climate change: Early Warning Signs- Coral Bleaching; 2005 October. [Cited 2006 Aug 10]. Available from: http://www.ucsusa.org/global_warming/science/early-warning-signs-of-global-warming-coral-reef-bleaching.html

Bureau of Oceans and International Environmental and Scientific Affairs. Coral Bleaching, Coral Mortality, and Global Climate Change; 1999 March. [Cited 2006 Aug 10]. Available from: http://yosemite.epa.gov/oar/globalwarming.nsf/content/ImpactsFisheries.html

Merle J. South Pacific Climate Variability and its Impact on Low-Lying Islands;
Date Unknown; [Cited 2006 Aug 10]. Available from: http://www.unesco.org.uy/phi/libros/enso/merle.html

Buddemeier RW & Fautin DG. 1993. Coral Bleaching as an Adaptive Mechanism: A testable hypothesis. Bioscience 43 (5): 320-326.



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