Abstract: A previous study has demonstrated that short-term blue light exposure enhances thermal bleaching tolerance in Acropora tenuis from Sanya, Hainan. However, whether this effect is universally applicable to corals from different reef regions and whether it is modulated by other light spectra remain unclear. In this study, we used Acropora muricata from Weizhou Island to investigate the effects of acclimation under different light quality (white, red, and blue light) followed by thermal stress, analyzing changes in holobiont phenotype, photosynthetic physiology, and antioxidant activity.Results showed: (1) After 7 days of light acclimation, no significant differences were observed among treatments in zooxanthellae density, chlorophyll a, or carotenoid content. However, photosynthetic efficiency and oxidative stress levels differed markedly—compared to white light, blue light reduced maximum quantum yield (Fv/Fm) by 4.2%, zooxanthellae reactive oxygen species (ROS) release by 10.0%, and malondialdehyde (MDA) content by 15.7%, while red light showed opposite trends with Fv/Fm increasing by 1.4%, ROS release by 15.0%, and MDA content by 5.3%. (2) On day 7 of thermal stress (32°C) following acclimation, white and red light corals exhibited visible color changes (shifting from dark brown to pale yellow with partial tissue bleaching), whereas blue light corals maintained their appearance and higher Fv/Fm. Compared to white light, blue light treatment resulted in 9.3%, 13.9%, and 18.3% higher zooxanthellae density, chlorophyll a, and carotenoid content, respectively, while red light showed reductions of 10.7%, 10.4%, and 2.3%. (3) Throughout thermal stress, blue light corals maintained the highest antioxidant enzyme activity and exhibited the lowest ROS and MDA levels on day 7 at 32°C.These results demonstrate that short-term acclimation under different light spectra differentially modulates holobiont thermal stress responses. Blue light acclimation enhances thermal tolerance inA. muricata by downregulating basal metabolism, elevating antioxidant enzyme levels, and reducing ROS accumulation. This study provides mechanistic insights into light-mediated coral thermal adaptation and offers scientific evidence for coral conservation strategies through light environment manipulation.

Key words: Global warming, Weizhou Island, Acropora muricata, light quality acclimation, thermal tolerance