Florida International University
Photosynthetic symbionts that inhabit coral tissues in great abundance may become damaged during periods of severe thermal stress. These situations lead to mass coral bleaching events often resulting in the mortality of numerous corals and subsequent degradation of the entire ecosystem they support. The discovery that some corals can harbor different species of symbiont with differing thermal sensitivity has led to the hypothesis that such variability could provide an axis for acclimatization or adaptation to climate change if corals can host thermally tolerant algae. In particular, it is thought that zooxanthellae (algae in the genus Symbiodinium) within the "D" lineage may serve this role, yet knowledge of the ecological distribution and physiological detail of this and other groups of zooxanthellae is largely incomplete. The eastern Pacific provides an excellent venue to test ideas of symbiont change and resilience, as it encompasses regions that have been differentially impacted by bleaching and has coral species known to harbor D-type zooxanthellae. Drs. Warner and LaJeunesse will investigate the distribution of different zooxanthellae within and between several populations of ecologically important reef-building corals in three regions of western Mexico with historical differences in bleaching frequency and severity. Genetic surveys at multiple temporal and spatial scales will utilize new methods for algal detection to characterize the full complement of zooxanthellae within chosen corals. The short and long-term impacts of thermal exposure on the photosynthetic activity and calcification of corals known to harbor multiple or single symbionts will be assessed, as will the potential for recovery from thermal stress via symbiont change. Lastly, fitness will be evaluated by investigating the growth and reproductive output of coral-algal combinations. The outcome of this research should provide much needed knowledge toward the question of how (or if) zooxanthellae and reef corals can survive future environmental disturbance based on predicted increases in sea water temperature. The proposed work represents a collaborative effort between U.S. and Mexican scientists and includes the training of two PhD students and several undergraduate students from the collaborating investigators' home institutions.
