Oxygen is a critical resource that mediates a multitude of essential processes and interactions at multiple scales on coral reefs. In adult corals, it can directly or indirectly impact physiological processes, such as photosynthesis, respiration, and calcification. Moreover, many corals bleach as a consequence of being exposed to low oxygen. The sessile adult phase of corals makes habitat selection crucial for post-settlement survival and thus their pelagic larvae use a diverse array of cues to determine a suitable spot for settlement. However, the effects of oxygen on the early life stages of corals are still poorly known. This study investigated the importance of oxygen as a potential settlement cue and its effect on swimming and settlement behavior of coral larvae of two Acropora species. Two experiments were performed, one investigating coral larval swimming behavior under different oxygen conditions and the other studying coral larval settlement along an oxygen gradient. Bottom exploration, expressed as the percent of A. cytherea and A. pulchra larvae in the bottom section of experimental cylinders, was reduced by 96% and 100%, respectively, in hypoxic water compared to normoxic water. When offered the choice to settle on an otherwise preferred settlement substrate ( Titanoderma prototypum ) along an oxygen gradient, larvae of both coral species settled almost exclusively on T. prototypum fragments placed in well-oxygenated environments, with settlement rates increasing nonlinearly with oxygen concentrations. These results suggest that low-oxygen areas can negatively influence the settlement success of coral larvae and that oxygen concentration may be used as a cue for coral larval swimming and settlement behavior.

中文翻译：

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珊瑚幼虫避免在低氧环境中探索和沉降

氧气是一种关键资源，可以在珊瑚礁的多个尺度上调节多种基本过程和相互作用。在成年珊瑚中，它可以直接或间接影响生理过程，如光合作用、呼吸作用和钙化。此外，许多珊瑚因暴露于低氧环境而漂白。珊瑚的无柄成虫阶段使得栖息地选择对定居后的生存至关重要，因此它们的远洋幼虫使用多种线索来确定适合定居的地点。然而，氧气对珊瑚早期生命阶段的影响仍然知之甚少。本研究调查了氧气作为潜在沉降线索的重要性及其对两种鹿角珊瑚物种的珊瑚幼虫游泳和沉降行为的影响。进行了两次实验，一个研究珊瑚幼虫在不同氧气条件下的游泳行为，另一个研究沿着氧气梯度的珊瑚幼虫沉降。与常氧水相比，在低氧水中，以 A. cytherea 和 A. pulchra 幼虫在实验缸底部的百分比表示的底部探索分别减少了 96% 和 100%。当可以选择沿着氧梯度在其他首选的沉降基质（ Titanoderma prototypum ）上定居时，两种珊瑚物种的幼虫几乎完全定居在放置在充氧环境中的 T. prototypum 碎片上，沉降率随氧浓度呈非线性增加。