MEPS prepress abstract  -  doi: 10.3354/meps07372

ABSTRACT: The objective of this study was to examine seasonal fluctuations of the maximum quantum yield (F_v/F_m), algal density and genotypic clade composition of zooxanthellae simultaneously in the sympatric corals Pavona divaricata and P. decussata at high latitude. The two species showed different responses to seasonal changes of light and seawater temperature. Pavona decussata was associated only with clade C zooxanthellae irrespective of sampling time while genotypic clade composition fluctuated in P. divaricata. Three colonies of P. divaricata harbored clade D throughout the year and other seven colonies changed clade type from C to D or vice versa, or contained a mixture of both clades of zooxanthellae at some sampling time. Though both corals did not suffer bleaching during the experimental period, P. decussata and P. divaricata harboring clade C showed a decrease in F_v/F_m during cold and warm seasons, while the F_v/F_m of P. divaricata harboring clade D was stable. When exposed to low or high temperature under normal or high light, P. divaricata harboring clade D showed less damage and faster recovery in photosystem II than P. decussata harboring clade C. These results suggest that the sympatric congeneric corals show different flexibilities with symbionts types and this difference might account for the observed difference in stress susceptibility between the two species. This study also shows that, in high-latitude reefs, both winter low temperatures and summer high temperatures may present potential stresses which cause coral bleaching at least to corals with high fidelity to clade C zooxanthellae.