Scientists from the University of Miami have discovered that coral bleaching makes the corals more susceptible to disease, and the diseases in turn make the coral more susceptible to bleaching.
Publishing their results in the latest issue of the journal Ecology, Marilyn Brandt and John McManus intensively monitored two patches of coral reefs in the Florida Keys for a period of 18 months for their study.
The period included a sustained spell of coral bleaching that was triggered by elevated water temperatures during August"November 2005.
The authors found that the prevalence of white plague disease in Montastraea faveolata increased during the bleaching event, a phenomenon they attributed to the decreased disease resistance brought about by the coral bleaching.
In colonies of Siderastrea siderea corals the authors found that those already infected with dark spot disease suffered more extensive bleaching than healthy coral.
It is thought that the fungus thought to be responsible for dark spot disease physiologically affects the coral to the point that they lose their zooxanthellae and bleach more readily when temperatures are high.
According to the authors, their results have ...provided greater insight into linkages between physiological responses of reef-building corals to thermal stress, and shed light on how bleaching and disease may interact during future anomalous thermal events.
For more information, see the paper: Brandt, ME and JW McManus (2009) Disease incidence is related to bleaching extent in reef-building corals. Ecology 90, pp. 2859"2867.