The role of symbiotic dinoflagellates in the temperature-induced bleaching response of Aiptasia pallida

Bleaching of reef corals and other cnidarians symbiotic with zooxanthellae can be attributed to the stress response of the host, algae or both. To determine if zooxanthellae are involved in the bleaching process, I infected a single strain of sea anemone, Aiptasia pallida with zooxanthellae from different hosts. I measured expulsion of the algae from the host during 24-hour incubations at 25, 32 and 34C, as well as photosynthetic rates at these temperatures. Photosynthesis and expulsion of zooxanthellae were inversely and directly proportional to elevated temperatures, respectively. Photosynthesis and expulsion of zooxanthellae isolated from Condylactis gigantea showed the greatest sensitivity to elevated temperature when compared to other zooxanthellae tested. These results suggest that zooxanthellae have a function in the bleaching process and that this function may be related to their photosynthetic response. Thus, the differential tolerance of zooxanthellae to stress could partly explain the spatial variability characteristic of coral-bleaching episodes.