Light is critical to coral growth through endosymbiont photosynthesis but can also act with elevated temperatures to cause coral bleaching. When more light is absorbed than can be used for photosynthesis, elevated irradiance can damage symbiont photosynthetic machinery. Hence, solar-radiation management through shading has been suggested to alleviate coral bleaching during marine heatwaves. Acropora divaricata and Acropora kenti were tested at two temperatures with 30% shading and an unshaded control to determine the relative impacts of light and temperature on coral bleaching severity. The coral bleaching response was assessed by photochemical (pulse amplitude modulated fluorometry), physiological (symbiont density, chlorophyll a concentration, catalase activity, and lipid peroxidation), and physical (mean intensity of grey or ‘percentage whiteness’) markers. Shading significantly reduced the bleaching response in A. divaricata, whilst for some parameters A. kenti responded negatively to shade. In A. divaricata, shading prevented photochemical collapse up to the experiment’s maximum 4.4 degree-heating weeks (DHW). Biomarkers of coral bleaching stress responded to shade and water temperature at 4.4 DHW; catalase activity was greatest in the shaded and ambient temperature treatment. Shading did not reduce the effects of bleaching in A. kenti; the mean intensity of grey and light saturation coefficient was greatest in the shaded treatment. Shading did, however, reduce lipid peroxidation at 3 DHW. Our results suggest shading during thermal stress may only protect some coral species, highlighting the need to consider species-specific responses when evaluating the potential efficacy of coral bleaching interventions.

中文翻译：

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热应激珊瑚的遮荫反应具有物种特异性


光通过内共生体光合作用对珊瑚生长至关重要，但也会在高温下导致珊瑚白化。当吸收的光多于可用于光合作用的光时，辐照度升高会损害共生体的光合作用机制。因此，有人建议通过遮阳进行太阳辐射管理，以减轻海洋热浪期间的珊瑚白化。在两种温度下对 Acropora divaricata 和 Acropora kenti 进行了测试，其中 30% 遮光和无遮光对照，以确定光和温度对珊瑚白化严重程度的相对影响。通过光化学（脉冲调幅荧光测定法）、生理学（共生体密度、叶绿素 a 浓度、过氧化氢酶活性和脂质过氧化）和物理（平均灰色强度或“白度百分比”）标记来评估珊瑚白化反应。遮荫显着降低了 A. divaricata 的漂白反应，而对于某些参数，A. kenti 对遮荫反应呈负面反应。在 A. divaricata 中，遮光可防止光化学崩溃，直至实验的最大 4.4 度加热周 (DHW)。珊瑚白化应激的生物标志物对 4.4 DHW 的遮荫和水温有反应；过氧化氢酶活性在遮荫和环境温度处理中最高。遮光并没有减少 A. kenti 的漂白效果；阴影处理的平均灰度强度和光饱和系数最大。然而，遮荫确实减少了 3 DHW 下的脂质过氧化。我们的结果表明，热应激期间的遮荫可能只能保护某些珊瑚物种，这凸显了在评估珊瑚白化干预措施的潜在功效时需要考虑物种特异性反应。