3.1Physiological response
The physiological response of Turbinaria peltata to MHWs stress was remarkable (Fig. 2). After the first MHWs, the density of zooxanthellae reduced about 79.44 % compared to the control group, and the concentration of Chl a decreased about 33.67 %. While, the levels of GST, Caspase-3, SOD, and CAT showed a significant increase. The effect of the second MHWs was less intense, as indicated by the slight decrease in density of zooxanthellae and concentration of Chl a , which showed about 69.71% and 17.63% decrease compared to the control group, respectively. Although there was an increase in levels of GST, Caspase-3, SOD, and CAT, it was not as high as those of the first heat stress. Compared to the first heat stress, the levels of GST and Caspase-3 exhibited a significant decrease (p < 0.05), and the levels of CAT and SOD also decreased although it’s not significant.
Fig. 2. Response of coral physiological indicators under different treatments. a: zooxanthellae, b: Chl a, c: GST, d: Caspase-3, e: CAT, f: SOD.