ELSEVIER Ecological Modelling 84 (1996) 199-214 EI:OLOI;li'IIL mODELLInl] Patterns of coral bleaching: modeling the adaptive bleaching hypothesis John R. Ware a, *, Daphne Gail Fautin b, Robert W. Buddemeier c a Computer Sciences Corporation, 1301 Piccard Drive, Rockville, MD 20850, USA b Department of Systematics and Ecology, University of Kansas, Lawrence, KS 66045, USA c Kansas Geological Survey, University of Kansas, Campus West, 1930 Constant Avenue, Lawrence, KS 66047, USA Received 1 March 1994; accepted 24 August 1994 Abstract Bleaching - the loss of symbiotic dinoflagellates (zooxanthellae) from animals normally possessing them - can be induced by a variety of stresses, of which temperature has received the most attention. Bleaching is generally considered detrimental, but Buddemeier and Fautin have proposed 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 model of this "adaptive bleaching hypothesis" provides insight into how animal-algae symbioses might react under various circumstances. It emulates many aspects of the coral bleaching phenomenon including: corals bleaching in response to a temperature only slightly greater than their average local maximum temperature; background bleaching; bleaching events being followed by bleaching of lesser magnitude in the subsequent one to several years; higher thermal tolerance of corals subject to environmental variability compared with those living under more constant conditions; patchiness in bleaching; and bleaching at temperatures that had not previously resulted in bleaching. Keywords: Adaptation; Coral bleaching; Marine ecosystems; Temperature 1. Introduction Under normal conditions, most reef-building corals are various shades of green or brown, colors primarily due to the intracellular symbiotic dinoflagellates known as zooxanthellae. These al- gae of uncertain taxonomy (e.g., Taylor, 1974; * Corresponding author. Fax: 301-670-2381. Blank and Trench, 1985; Rowan and Powers, 1991) provide metabolic benefits to their hosts (e.g., Land et al., 1975; Gattuso and Jaubert, 1990; Muscatine, 1990) and enhance coral calcifi- cation (e.g., Goreau and Goreau, 1959; Yonge, 1973; Vandermeulen and Muscatine, 1974). A coral is said to have bleached when the density of zooxanthellae declines so the white coral skeleton is visible through the coral tissue. (Reduced con- centration of algal chlorophyll can also produce 0304-3800/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 0304-3800(94)00132-4