Coral Bleaching Case Study

by salbe1 on April 17, 2015 - 3:32pm

Case Study:

A case study was done by Depczynski et al. between 2010 and 2011 after a particularly strong La Nina even had occurred. It resulted in a notable movement of warm tropical waters to the Western Australian coastline which caused an increase of up to five degrees Celsius in sea water temperature.  There were two sites that were studied in the Bundegi fringing reef, in Ningaloo Marine Park. There were six, 30 meter transects that were surveyed at depths between two and five meters. The surveys were taken in January 2010 which was pre bleaching, January 2011 which was during bleaching, April 2011 which was directly after bleaching and July 2011  which was post beaching. There were ninety images taken at each sample site which were analyzed and used to classify each reefs condition. The reefs were classified as alive, bleached, injured or dead. The results of this study showed that there was a large decline (72-92%) of live coral in January 2011 and it was concluded that this was primarily due to the warmer than average sea water temperatures.

Depczynski, M, Gilmour JP, Ridgway, T, Barnes H, Heyward AJ, Holmes TH, et al. 2013. Bleaching, coral mortality and subsequent survivorship on a West Australian fringing reef. Coral Reefs 32:233-8.

Why is this important?

This case study is proof that there is a direct relationship between rising sea temperatures and coral bleaching which can lead to mortality. As mentioned in a previous post though, corals can bounce back from a bleaching event if water temperatures return to normal in a timely manor. How does it happen though? The main mechanism corals use to rebuild is through the process of multiplication of the few surviving zooxanthallae left in the corals tissues, once back to its normal stage corals may go about life. Although corals can survive bleaching there are consequences. Bleached corals have much lower reproduction rates, growth rates and immunity to pathogens than non-bleached corals. So, it is important that we stop bleaching from happening rather than waiting and trying to repair bleached reefs!

Marshall, PA, Schuttenburg, H. 2006. Coral Bleaching - A review of the Causes and Consequences. A reef manager's guide to coral bleaching. Great Barrier Reef Marine Park Authority.



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