| Summary: | Most laboratory experiments examining the effect of ocean acidification on marine organisms use stable pH/pCO(2)treatments based on average projections for the open ocean. However, pH/pCO(2)levels vary spatially and temporally in marine environments, and this variation can affect organism responses to pH/pCO(2). On coral reefs, diel pH/pCO(2)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/pCO(2)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 pH(T)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 dielpCO(2)cycle, increasing overnight and decreasing during the day, in association with photosynthesis and respiration cycles. DielpCO(2)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 inpCO(2)(Delta 250 mu atm) than the exposed (high flow) reefs (Delta 116 mu atm). These results add to a growing body of the literature on the diel variation ofpCO(2)of shallow, nearshore environments and suggest that when projecting futurepCO(2)levels, it is important to consider reef metabolism as well as physical and hydrodynamic factors.
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