The Effect of Seasonal Temperature Changes on the Light-Use Efficiency of Two Coral Communities
Saraceno, Hannah McKenzie
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Saraceno, Hannah McKenzie
Coral reefs continue to decline due to threatening human-related activities. Despite a general awareness of mass coral bleaching, intervention efforts have not effectively targeted the causes of reef decline. In order to identify specific stressors on reefs, additional assessment methods are required. The proposed method in this study is determining coral condition through light-use efficiency (LUE). To develop this method for reefs and determine the effects of seasonal temperatures, two coral communities were collected from offshore Bermuda and placed in an indoor racetrack flume. The first community was collected in the summer and placed in 28°C seawater, while the second community was collected during fall and placed in 25°C seawater, the ambient temperatures of their environment. The daily LUE for each community was measured and compared to determine if seasonal temperatures affect LUE. Primary production and absorbed photosynthetically available radiation (APAR) were also measured in order to detect which component of LUE may have changed. The community in the 28°C seawater was found to have a significantly higher LUE than the community in the 25°C seawater (p<0.01). Primary productivity of the 28°C community was also an average of 1.5 times higher than the productivity of the 25°C community at the same levels of APAR. However, the LUE of the corals in 25°C had a significant linear increase over the eleven days they were studied (p=0.016), suggesting that the community was still acclimating to the flume. If the study had continued, it is possible there may not have been a significant difference in the LUE of the two communities. The results of this study suggested that temperature change from fall to summer increased the LUE and therefore influenced the primary productivity of the communities. It was hypothesized that this result only occurs until a threshold temperature is reached, at which point bleaching and coral mortality occurs. This has implications for projected temperature increases due to climate change and further studies can determine whether these changes will lead to coral bleaching or increased primary production. This study suggests that LUE has the potential for measuring the sub lethal effects of specific stressors on coral reefs in order to better target intervention efforts for impacts to coral reefs.