Bleaching of corals on the Great Barrier Reef: differential susceptibilities among taxa

Large-scale coral bleaching episodes are potentially major disturbances to coral reef systems, yet a definitive picture of variation in assemblage res ponse and species susceptibilities is still being compiled. Here, we provid e a detailed analysis of the bleaching response of 4160 coral colonies, rep resenting 45 genera and 15 families, from two depths at four sites on reefs fringing inshore islands on the Great Barrier Reef. Six weeks after the on set of large-scale bleaching in 1998, between 11 and 83% of colonies along replicate transects were affected by bleaching, and mortality was 1 to 16%. There were significant differences in bleaching response between sites, de pths and taxa. Cyphastrea, Turbinaria and Galaxea were relatively unaffecte d by bleaching, while most acroporids and pocilloporids were highly suscept ible. The hydrocorals (Millepora spp.) were the most susceptible taxa, with 85% mortality. Spatial variation in assemblage response was linked to the taxonomic composition of reef sites and their bleaching history. We suggest , therefore, that much of the spatial variation in bleaching response was d ue to assemblage composition and thermal acclimation.