4.1 Physiological Adaptation of Turbinaria peltata to marine heatwaves
Recent studies have provided increasing evidence for the adaptive capacity of corals to heat stress (Yu et al., 2020; Hackerott et al., 2021; Schoepf et al., 2022). This adaptability primarily relies on the thermal tolerance of their symbiotic algae, with susceptible populations being expelled while those remaining show enhanced metabolic activity and photosynthetic efficiency to cope with high temperatures (Perniceet al., 2012; Arandia-Gorostidi et al., 2017; Stanley and van de Schootbrugge, 2018). In our study, the initial exposure to MHWs resulted in a significant decrease in the density of diatoms (p < 0.05). However, the second exposure to MHWs provided relief from this impact. Furthermore, corals regulate the synthesis and activity of antioxidant enzymes, such as superoxide SOD, CAT, and GST, as well as apoptotic proteases like Caspase-3, to counteract acute heat stress (Bhagooli and Hidaka, 2004; Lesser, 2006; Thummasan et al., 2021). The initial exposure to MHWs led to a significant increase (p < 0.05) in the levels of GST, Caspase-3, SOD, and CAT. However, the effects were alleviated upon subsequent exposure to MHWs. This regulatory process helps in clearing excessive reactive oxygen species (ROS), thereby maintaining normal cellular function and physiological state. Consequently, repetitive exposure to heatwaves imposes less physiological stress on corals compared to their initial exposure (Xu et al., 2021), indicating potential physiological adaptations ofTurbinaria peltata to withstand MHWs.