| Summary: | 碩士 === 國立東華大學 === 海洋生物科技研究所 === 98 === Coral bleaching has been studied for decades. The breakdown of endosymbiosis between cnidarian hosts and their symbionts (Symbiodinium) is commonly triggered by environmental stress, and elevated water temperature is the first-order threat to coral reefs. Under stress conditions, different corals may display different bleaching levels. Recent studies have found that coral bleaching is triggered by the dysfunctional algae. In this study, we used flow-cytometry and pulse-amplitude-modulated (PAM) fluorometry to compare the responses of two clades of Symbiodinium exposed to various temperatures.
We found that the percentage of clade A Symbiodinium cells in G2/M phase at 18°C is significantly lower than that at 24°C in 2 continuous L/D cycles. At higher temperature (i.e. 28 and 32°C), the percentage of clade A cells in G2/M phase remained the same. Clade B Symbiodinium, however, had a lower percentage in the first L/D cycle at 18°C but recovered in the second cycle. At 28°C, the percentage of cells in G2/M was significantly higher in both cycles. At an even higher temperature (32°C), clade B cells had much lower percentage of cells in G2/M phase. In addition, the photosynthesis capacity, as measured by Fv/Fm, of both clade A and B correlated to the changes in percentage of cells in G2/M phase in response to changes in temperature.
The decreased photosynthetic capacity may play an important role in the response of Symbiodinium cell proliferation at low temperature. However, at elevated temperatures, there are other factors contributing to Symbiodinium cell proliferation.
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