Laboratoire de Biologie Marine, Université Libre de Bruxelles, Avenue F.D. Roosevelt 50, CP160/15, 1050, Bruxelles, Belgium.
Laboratoire de Biologie Marine, Université Libre de Bruxelles, Avenue F.D. Roosevelt 50, CP160/15, 1050, Bruxelles, Belgium.
Mar Environ Res. 2023 Feb;184:105851. doi: 10.1016/j.marenvres.2022.105851. Epub 2022 Dec 23.
Local thermal environment has a strong influence on the physiology of marine ectotherms. This is particularly relevant for tropical organisms living close to their thermal optimum, well exemplified by the increasing frequency of bleaching occurrence in shallow-water corals. Mesophotic Coral Ecosystems (MCEs) were suggested as potential oases, especially when they are submitted to internal waves inducing short-term cooling events. Indeed, probability of bleaching occurrence in scleractinians was reported to decrease with depth in Mo'orea as temperature variability increases. However, ecophysiological data are currently lacking to understand the cause of lower susceptibility/increased plasticity of deeper corals. A growing interest has been devoted the last decade to MCEs, but our understanding of the physiological performance of benthic organisms living in this environment remains relatively unexplored. To tackle that question, we first compared the metabolic responses (dark respiration, net photosynthesis and photosynthetic efficiency) of the depth-generalist scleractinian Pachyseris speciosa from two heterogeneous thermal environment (25 and 85 m depths) to acute heat stress to determine if the local thermal environment could predict coral response to warming. Then, we tested the thermal performance of two sympatric species (the scleractinian P. speciosa and the antipatharian Stichopathes sp.) to determine if there are inter-species differences in performances in species experiencing identical levels of temperature variability, at mesophotic depths (85 m). Results revealed broader thermal performances in the mesophotic P. speciosa compared to mid-depth ones, and constrained performances in the mesophotic antipatharian compared to the scleractinian species. We hypothesize that the high fluctuations in temperature due to internal waves in deeper areas contribute to the broader thermal performances of mesophotic P. speciosa. However, the constrained performances of the mesophotic antipatharian compared to P. speciosa suggests that other processes than the symbiosis with zooxanthellae also influence thermal performances of these mesophotic organisms. Our results supported that Stichopathes sp. lives close to its thermal optimum, suggesting a (relatively) cold thermal specialist strategy. In this context, composition of MCEs in the future is unlikely to shift to antipatharian-dominated landscape and will remain coral-dominated landscape.
局部热环境对海洋变温动物的生理有很强的影响。这对于生活在接近热最佳点的热带生物尤其重要，浅水珊瑚中漂白现象发生频率的增加就是很好的例证。中深层珊瑚礁生态系统（MCEs）被认为是潜在的绿洲，尤其是当它们受到内部波引起的短期冷却事件的影响时。事实上，在莫雷阿岛，随着温度变异性的增加，石珊瑚发生漂白的概率随着深度的增加而降低。然而，目前缺乏关于更深层次珊瑚较低易感性/更高可塑性的生态生理学数据。过去十年中，人们对 MCEs 的兴趣日益浓厚，但我们对生活在这种环境中的底栖生物的生理表现的理解仍然相对未知。为了解决这个问题，我们首先比较了两种异质热环境（25 和 85 米深度）下深度通用石珊瑚 Pachyseris speciosa 的代谢反应（黑暗呼吸、净光合作用和光合作用效率）对急性热应激的反应，以确定局部热环境是否可以预测珊瑚对变暖的反应。然后，我们测试了两种共生种（石珊瑚 P. speciosa 和 antipatharian Stichopathes sp.）的热性能，以确定在中深层（85 米）经历相同温度变异性水平的物种中，是否存在种间差异的性能。结果表明，与中深层的相比，中深层的 P. speciosa 具有更广泛的热性能，而中深层的 antipatharian 的性能受到限制。我们假设，由于内部波在更深的区域导致温度的高波动，这有助于中深层 P. speciosa 更广泛的热性能。然而，与石珊瑚物种相比，中深层 antipatharian 的受限性能表明，除了与虫黄藻共生之外，其他过程也会影响这些中深层生物的热性能。我们的结果支持 Stichopathes sp. 生活在接近热最佳点的假设，表明了一种（相对）冷的热专家策略。在这种情况下，未来 MCEs 的组成不太可能向 antipatharian 主导的景观转变，而将保持珊瑚主导的景观。
