Fluctuating algal symbiont communities in Acropora palifera (Scleractinia: Acroporidae) from Taiwan

Seasonal dynamics of algal symbiont communities from the reef flat-dwelling coral Acropora palifera was monitored from January 2000 to July 2001 at Tantzei Bay, Kenting National Park, southern Taiwan. Zooxanthellae density and pigment contents monitored throughout the 18 mo sampling period indicated that no significant bleaching occurred in A. palifera. Molecular phylotyping showed that 2 distinct symbionts, Phylotypes C and D, were associated with A. palifera, either individually or simultaneously. Population surveys throughout the bimonthly sampling period demonstrated that the symbiont community within A. palifera was highly dynamic with significant fluctuations; a drop in the Phylotype D percentage occurred in May, which was correlated with a rise in seawater temperature in the late spring/early summer at the sampled reef. Direct tracking of tagged corals provided evidence that seasonal fluctuations in the algal symbiont communities not only involve changes in zooxanthellae densities and pigment contents, but also a reshuffling of different Symbiodinium phylotypes. Our study highlights that stress tolerance among phylotypes urgently needs to be re-evaluated through a better understanding of the physiological traits of symbionts.