School of Health and Human Sciences, Southern Cross University, Gold Coast, QLD, 4225, Australia; Marine Ecology Research Centre, Southern Cross University, Lismore, NSW, 2480, Australia.
Université Pierre et Marie Curie, Paris, 75005, France.
Mar Environ Res. 2020 Jun;158:104947. doi: 10.1016/j.marenvres.2020.104947. Epub 2020 Mar 12.
Heat stress is an environmental factor that regularly challenges the well-being of living organisms. This study aims to examine the physiological changes happening in two reef-building coral species exposed to thermal stress under various light conditions. The two ecologically relevant heatwave scenarios were applied under ambient lights (high irradiance) and reduced light conditions (250 and < 10 μmol photons m s). Corals were exposed to elevated temperatures of 32°C (plus 6°) for a period of 1 up to 5 days corresponding to heatwaves reported on the Great Barrier Reef (GBR) that were associated with coral bleaching. We monitored changes in the physiological performance of these two coral species by measuring symbionts and corals' physiological parameters including symbiont density, levels of multiple algal pigments (chlorophyll a and peridinin), as well as the changes in the host protein concentration. During the short-term heat stress, both species were with stable physiological performance with the only exception of Stylophora pistillata under ambient lights. These results show that S. pistillata was negatively influenced by a synergistic effect of temperature and high irradiance resulting in the first signs of bleaching after only 24h of thermal stress. Exposure to prolonged thermal stress, characterised with a slower rate of temperature increase, affected both coral species investigated and resulted in bleaching mainly by day 5. Interestingly, severe light reduction (<10 μmol photons m s) made Acropora millepora corals more thermally sensitive and resulted in earlier signs of bleaching (on day 3). These findings indicate that there was a synergistic effect of very low lights and thermal stress that caused higher levels of bleaching in A. millepora. Our results revealed differential thermal sensitivity for two branching corals exposed to different thermal stress scenarios under various light irradiance conditions, naturally found in their existing habitats. Consequently, global warming may have a differential impact on coral reef biodiversity depending on light availability.
热应激是一种经常挑战生物生存福祉的环境因素。本研究旨在研究两种造礁珊瑚在不同光照条件下暴露于热应激时发生的生理变化。在环境光（高辐照度）和低光条件（250 和 <10 μmol 光子 m s）下应用了两种具有生态相关性的热浪情景。珊瑚暴露在 32°C（升高 6°C）的高温下长达 1 至 5 天，对应于大堡礁报告的与珊瑚白化相关的热浪。我们通过测量共生体和珊瑚的生理参数来监测这两种珊瑚物种的生理性能变化，包括共生体密度、多种藻类色素（叶绿素 a 和 peridinin）水平，以及宿主蛋白浓度的变化。在短期热应激期间，除了在环境光下的 Stylophora pistillata 外，两种珊瑚的生理性能都很稳定。这些结果表明，S. pistillata 受到温度和高光辐照度协同效应的负面影响，在热应激仅 24 小时后就出现了首次白化迹象。暴露于延长的热应激中，其特征是温度上升速度较慢，这两种研究的珊瑚物种都受到影响，并在第 5 天主要导致白化。有趣的是，严重的光照减少（<10 μmol 光子 m s）使 Acropora millepora 珊瑚对热更敏感，并导致更早出现白化迹象（第 3 天）。这些发现表明，在非常低的光照和热应激下存在协同效应，导致 A. millepora 白化程度更高。我们的研究结果表明，两种分枝珊瑚在不同光照辐照度条件下暴露于不同的热应激情景下，表现出不同的热敏感性，这与它们现有的栖息地中自然存在的情况一致。因此，全球变暖可能会根据光照条件对珊瑚礁生物多样性产生不同的影响。
