Abstract：
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.
摘要：
局部热环境对海洋外温的生理影响很大。这对于生活在接近其最佳温度的热带生物尤其重要，在浅水珊瑚中漂白发生的频率越来越高。中观珊瑚生态系统（MCE）被认为是潜在的绿洲，特别是当它们被提交到内部波诱导短期冷却事件。的确,据报道，随着温度变化的增加，巩膜中漂白发生的可能性随着Mo\'orea深度的增加而降低。然而,目前缺乏生态生理数据来了解更深珊瑚的敏感性较低/可塑性增加的原因。在过去的十年里，越来越多的人对MCE感兴趣，但是我们对生活在这种环境中的底栖生物的生理表现的理解还没有被探索。为了解决这个问题，我们首先比较了代谢反应(黑暗呼吸，净光合作用和光合效率）从两个异质热环境（25和85m深度）到急性热胁迫的深度通才巩膜Pachyserisspeciosa，以确定局部热环境是否可以预测珊瑚对变暖的响应。然后，我们测试了两种同胞物种的热性能（巩膜虫P.speciosa和反patharianStichopathessp.)以确定经历相同温度变化水平的物种的表现是否存在物种间差异，在介观深度（85米）。结果表明，与中等深度的相比，中观speciosa的热性能更广泛，与巩膜物种相比，中隔抗病动物的表现受到限制。我们假设，由于较深区域的内部波引起的温度高波动会导致介孔P.speciosa的更广泛的热性能。然而,与P.speciosa相比，介孔抗病菌的受限性能表明，与虫黄藻共生以外的其他过程也会影响这些介孔生物的热性能。我们的结果支持Stichopathessp。寿命接近其热最佳值，建议(相对)冷热专家策略。在这种情况下，未来MCE的组成不太可能转向以反病态为主的景观，并将继续以珊瑚为主的景观。
