THE EFFECTS OF ELEVATED-TEMPERATURE ON THE PHOTOSYNTHETIC EFFICIENCY OF ZOOXANTHELLAE IN HOSPITE FROM 4 DIFFERENT SPECIES OF REEF CORAL - ANOVEL-APPROACH

Bleaching of reef corals is a phenomenon linked to temperature stress which involves loss of the symbiotic algae of the coral, which are kno wn as zooxanthellae, and/or loss of algal pigments, The photosynthetic efficiency of zooxanthellae within the corals Montastrea annularis, A garicia lamarki, Agaricia agaricites and Siderastrea radians was exami ned by pulse-amplitude modulation fluorometry (PAM) during exposure to elevated temperatures (30-36 degrees C). Zooxanthellae within M. annu laris and A. lamarki were found to be more sensitive to elevated tempe rature, virtually complete disruption of photosynthesis being noted du ring exposure to temperatures of 32 and 34 degrees C. The photosynthet ic efficiency of zooxanthellae within S. radians and A. agaricites dec reased to a lesser extent, Differences in the loss of algal cells on a n aerial basis and in the cellular chlorophyll concentration were also found between these species. By combining the noninvasive PAM techniq ue with whole-cell fluorescence of freshly isolated zooxanthellae, we have identified fundamental differences in the physiology of the symbi onts within different species of coral. Zooxanthellae within M. annula ris appear to be more susceptible to heat-induced damage at or near th e reaction centre of Photosystem II, while zooxanthellae living in S. radians remain capable of dissipating excess excitation energy through non-photochemical pathways, thereby protecting the photosystem from d amage during heat exposure.