Temperature-induced bleaching of corals begins with impairment of the CO2 fixation mechanism in zooxanthellae. Plant Cell Environ

The early effects of heat stress on the photosynthesis of symbiotic dinoflagellates (zooxanthellae) within the tis-sues of a reef-building coral were examined using pulse-amplitude-modulated (PAM) chlorophyll fluorescence and photorespirometry. Exposure of Stylophora pistillata to 33 and 34 oC for 4 h resulted in (1) the development of strong non-photochemical quenching (qN) of the chloro-phyll fluorescence signal, (2) marked decreases in photo-synthetic oxygen evolution, and (3) decreases in optimal quantum yield (FJF,) of photosystem II (PSII). Quantum yield decreased to a greater extent on the illu-minated surfaces of coral branches than on lower (shaded) surfaces, and also when high irradiance intensi-ties were combined with elevated temperature (33 “C a