The role of symbiotic dinoflagellates in the temperature-induced bleachingresponse of the subtropical sea anemone Aiptasia pallida

Coral bleaching involves the loss of symbiotic dinoflagellates (zooxanthell ae) from reef corals and other cnidarians and may be a stress response of t he host, algae or both. To determine the role of zooxanthellae in the bleac hing process, aposymbiotic sea anemones from Bermuda (Aiptasia pallida) wer e infected with symbionts from other sea anemones (Aiptasia pallida from Fl orida, Bartholomea annulata and Condylactis gigantea). The expulsion of alg ae was measured during 24-h incubations at 25, 32 and 34 degreesC. Photosyn thetic rates of freshly isolated zooxanthellae were also measured at these temperatures. The C. gigantea (Cg) symbionts were expelled in higher number s than the other algae at 32 degreesC. Photosynthesis by the Cg algae was c ompletely inhibited at this temperature, in contrast to the other symbionts . At 34 degrees all of the symbionts had increased expulsion rates, and at this temperature only the symbionts from Florida A. pallida exhibited any p hotosynthesis. These results provide the first evidence that the differenti al release of symbionts from the same host species is related to decreased photosynthesis at elevated temperatures, and support other findings suggest ing that zooxanthellae are directly affected by elevated temperatures durin g bleaching events. (C) 2001 Elsevier Science BN. All rights reserved.