The effects of thermal anomalies on tropical coral endosymbiosis can be mediated by a range of environmental factors, which in turn ultimately influence coral health and survival. One such factor is the water flow conditions over coral reefs and corals. Although the physiological benefits of living under high water flow are well known, there remains a lack of conclusive experimental evidence characterizing how flow mitigates thermal stress responses in corals. Here we use in situ measurements of flow in a variety of reef habitats to constrain the importance of flow speeds on the endosymbiosis of an important reef building species under different thermal regimes. Under high flow speeds (0.15 m s−1) and thermal stress, coral endosymbionts retained photosynthetic function and recovery capacity for longer compared to low flow conditions (0.03 m s−1). We hypothesize that this may be due to increased rates of mass transfer of key metabolites under higher flow, putatively allowing corals to maintain photosynthetic efficiency for longer. We also identified a positive interactive effect between high flow and a pre-stress, sub-lethal pulse in temperature. While higher flow may delay the onset of photosynthetic stress, it does not appear to confer long-term protection; sustained exposure to thermal stress (eDHW accumulation equivalent to 4.9°C weeks) eventually overwhelmed the coral meta-organism as evidenced by eventual declines in photo-physiological function and endosymbiont densities. Investigating flow patterns at the scale of metres within the context of these physiological impacts can reveal interesting avenues for coral reef management. This study increases our understanding of the effects of water flow on coral reef health in an era of climate change and highlights the potential to learn from existing beneficial bio-physical interactions for the effective preservation of coral reefs into the future.

中文翻译：

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高流量条件介导亚致死热应激对珊瑚内共生藻类的破坏性影响

热异常对热带珊瑚内共生的影响可以由一系列环境因素介导，这反过来最终影响珊瑚的健康和生存。其中一个因素是珊瑚礁和珊瑚上的水流条件。尽管生活在高水流下的生理益处是众所周知的，但仍然缺乏确凿的实验证据来描述水流如何减轻珊瑚的热应激反应。在这里，我们使用各种珊瑚礁栖息地中的流量的原位测量来限制流速对不同热状态下重要的珊瑚礁建造物种的内共生的重要性。在高流速（0.15 ms-1）和热应力下，与低流速条件（0.03 ms-1）相比，珊瑚内共生体保留光合功能和恢复能力的时间更长。我们假设这可能是由于在较高流量下关键代谢物的传质速率增加，假定珊瑚可以更长时间地保持光合效率。我们还确定了高流量和预应力、亚致死温度脉冲之间的积极交互作用。虽然较高的流量可能会延迟光合胁迫的发生，但它似乎并不能提供长期保护；持续暴露于热应力（eDHW 积累相当于 4.9°C 周）最终压倒了珊瑚元生物，光生理功能和内共生体密度的最终下降就是证明。在这些生理影响的背景下研究米级的流动模式可以揭示珊瑚礁管理的有趣途径。