MEPS 158:51-59 (1997)  -  doi:10.3354/meps158051

Changes in zooxanthellar densities and chlorophyll concentrations in corals during and after a bleaching event

Ross J. Jones*

Department of Biochemistry, James Cook University, Townsville, Queensland 4811, Australia
*Present address: School of Biological Sciences, Building A08, University of Sydney, Sydney, New South Wales 2006, Australia. E-mail:

In January 1994 a coral bleaching event occurred on the reefs of Magnetic Island (Australia) immediately after a period of anomalously high air temperatures. Average daily water temperature increased by 2°C over 1 wk, reaching 34°C (reef flat) and 32°C (reef slope). Bleached corals were observed soon afterwards, suggesting the bleaching event was temperature related. Bleached (light tan coloured) and unbleached (dark brown coloured) colonies of staghorn coral Acroporaformosa sampled during and after the bleaching event had lower zooxanthellar densities and higher chlorophyll a (chl a) concentrations per zooxanthella than the same colonies sampled 10 mo after the bleaching event. Significant increases in zooxanthellar chl a concentrations were measured in 2 colonies which were sampled and found to be losing zooxanthellae during the event. Intrinsic differences in the densities, chlorophyll concentrations and zooxanthellar cell sizes between neighbouring colonies of the same species resulted in intraspecific variability in coral discolouration during the bleaching event.


Bleaching · Chlorophyll · Coral · Temperature · Zooxanthellae


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