The Impacts of Temperature Changes on the Coral Astrangia poculata

With fluctuating temperatures due to climate change, corals worldwide are experiencing massive coral bleaching events. Corals lose a symbiotic relationship they have with Symbiodinium sp. and eventually starve and die. Astrangia poculata can tolerate large temperature fluctuations unlike its tropical cousins and naturally exist in both symbiotic and aposymbiotic states. We analyzed physiological attributes of A. poculata at warm, cold, and changing temperatures to determine how it adapts to temperature fluctuations. We measured critical parameters (buoyant weight, photosynthetic yield, and density of symbionts) before and after a temperature change. We tested cold and warm temperature acclimation in corals that were held at constant cold or warm temperatures of 13ºC and 27ºC respectively, by moving corals from 27ºC down to 13ºC, and from 13ºC up to 27ºC. This experiment showed, despite exceptions, an overall decrease in the weight, photosynthetic yield, and symbiont density after a temperature change. Warming the corals had greater impact, with a mortality rate of 100% after 29 days. We used confocal microscopy imaging of the corals and isolated Symbiodinium sp. with a reactive oxygen species (ROS) sensitive dye to analyze the degree of stress on the corals. The greatest amount of ROS was in the warmer corals at 26ºC around the mouth and on the tentacles, however this may be due to autofluorescence. More experiments are needed to determine the source of the fluorescence. We also measured the photosynthetic yield of the symbionts over a 24 hour period at various temperatures. Overall, this experiment showed a cold shock at 13ºC to have the greatest impact on the symbionts, with a decrease in the photosynthetic yield over the 48 hours. This project will aid in understanding how A. poculata can withstand widely fluctuating temperatures, the role of host and symbiont in the response, and how temperature changes impact corals in general.