PATTERNS OF CORAL BLEACHING - MODELING THE ADAPTIVE BLEACHING HYPOTHESIS

Bleaching - the loss of symbiotic dinoflagellates (zooxanthellae) from animals normally possessing them - can be induced by a variety of str esses, of which temperature has received the most attention. Bleaching is generally considered detrimental, but Buddemeier and Fautin have p roposed that bleaching is also adaptive, providing an opportunity for recombining hosts with alternative algal types to form symbioses that might be better adapted to altered circumstances. Our mathematical mod el of this ''adaptive bleaching hypothesis'' provides insight into how animal-algae symbioses might react under various circumstances. It em ulates many aspects of the coral bleaching phenomenon including: coral s bleaching in response to a temperature only slightly greater than th eir average local maximum temperature; background bleaching; bleaching events being followed by bleaching of lesser magnitude in the subsequ ent one to several years; higher thermal tolerance of corals subject t o environmental variability compared with those living under more cons tant conditions; patchiness in bleaching; and bleaching at temperature s that had not previously resulted in bleaching.