Acclimation to Thermal Stress in Reef-Building Corals

What was done
The authors collected branches of the reef-building coral Acropora aspera -- which contains the dinoflagellate symbiont Symbiodinium (clade C3) -- from three large colonies on the reef flat adjacent to the Heron Island Research Station at the southern end of Australia's Great Barrier Reef. Multiple upward-growing branch tips were placed on racks immersed in running seawater within four 750-liter tanks that were maintained at the mean local ambient temperature (27°C) and exposed to natural reef-flat summer daily light levels. Then, two weeks prior to a simulated bleaching event -- where water temperature was raised to a value of 34°C for a period of six days -- they boosted the water temperature in one of the tanks to 31°C for 48 hours, while in another tank they boosted it to 31°C for 48 hours one week before the simulated bleaching event. In the third tank they had no pre-heating treatment, while in the fourth tank they had no pre-heating nor any simulated bleaching event. At different points throughout the study, they measured photosystem II efficiency, xanthophyll and chlorophyll a concentrations, and Symbiodinium densities.
What was learned...[CO2 Science]