Most laboratory experiments examining the effect of ocean acidification on marine organisms use stable pH/pCO2 treatments based on average projections for the open ocean. However, pH/pCO2 levels vary spatially and temporally in marine environments, and this variation can affect organism responses to pH/pCO2. On coral reefs, diel pH/pCO2 variability at the individual reef scale has been reported in a few studies, but variation among microhabitats within a reef remains poorly understood. This study determined the pH/pCO2 variability of three different reefs, and three contrasting coral reef microhabitats (dominated by hard coral, soft coral, or open substrate) within each reef. Three SeaFET pH loggers were deployed simultaneously at the three microhabitats within a reef over a 9-day period. This was repeated at three different reefs around the Lizard Island lagoon. The loggers recorded pHT and temperature every 5 min. Water samples were collected from each microhabitat during four points of the tidal cycle (high, low, rising, and falling) and analysed for total alkalinity and dissolved inorganic carbon. The data show a clear diel pCO2 cycle, increasing overnight and decreasing during the day, in association with photosynthesis and respiration cycles. Diel pCO2 differed more between reefs than between microhabitats within reefs. Variation between reefs was most likely influenced by water flow, with the more protected (low flow) reefs experiencing a greater range in pCO2 (Δ 250 μatm) than the exposed (high flow) reefs (Δ 116 μatm). These results add to a growing body of the literature on the diel variation of pCO2 of shallow, nearshore environments and suggest that when projecting future pCO2 levels, it is important to consider reef metabolism as well as physical and hydrodynamic factors.

中文翻译：

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大堡礁蜥蜴岛珊瑚礁和微生境的 Diel pCO2 变化

大多数检查海洋酸化对海洋生物影响的实验室实验使用基于公海平均预测的稳定 pH/pCO2 处理。然而，海洋环境中的 pH/pCO2 水平随空间和时间而变化，这种变化会影响生物体对 pH/pCO2 的反应。在珊瑚礁上，一些研究报告了单个珊瑚礁规模的 diel pH/pCO2 变化，但对珊瑚礁内微生境之间的变化知之甚少。这项研究确定了三个不同珊瑚礁的 pH/pCO2 变异性，以及每个珊瑚礁内三个对比鲜明的珊瑚礁微生境（以硬珊瑚、软珊瑚或开放基质为主）。在 9 天的时间里，三个 SeaFET pH 记录仪同时部署在珊瑚礁内的三个微生境中。这在蜥蜴岛泻湖周围的三个不同珊瑚礁上重复进行。记录器每 5 分钟记录一次 pHT 和温度。在潮汐循环的四个点（高、低、上升和下降）从每个微生境收集水样，并分析总碱度和溶解的无机碳。数据显示了一个清晰的 diel pCO2 循环，夜间增加，白天减少，与光合作用和呼吸循环有关。Diel pCO2 在珊瑚礁之间的差异比在珊瑚礁内的微生境之间的差异更大。珊瑚礁之间的变化最有可能受到水流的影响，受保护的（低流量）珊瑚礁的 pCO2（Δ 250 μatm）范围比暴露（高流量）的珊瑚礁（Δ 116 μatm）更大。这些结果增加了越来越多关于浅层 pCO2 变化的文献，