Bleaching Resistance and the Role of Algal Endosymbionts

Abstract

Scleractinian corals and octocorals form mutualistic endosymbioses with singlecelled dinoflagellate algae in the genus Symbiodinium. This association is obligate in most coral species, with the coral host capable of deriving over 90% of its energy budget from its algal endosymbionts (Muscatine and Porter 1977), although nutritional dependence on Symbiodinium is generally lower in octocorals (Fabricius and Klumpp 1995). These endosymbionts also play a vital role in the light-enhanced calcification of scleractinian corals (Barnes and Chalker 1990; Moya et al. 2006). In healthy corals, Symbiodinium typically occur at extremely high densities (>106 cells per cm2 coral tissue). During bleaching events, symbiont photosynthetic pathways become impaired (Chap. 8), leading to a breakdown in the symbiosis resulting in the...