Diel p CO 2 variation among coral reefs and microhabitats at Lizard Island, Great Barrier Reef
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Diel pCO2 variation among coral reefs and microhabitats at Lizard Island, Great Barrier Reef Kelly D. Hannan1 • Gabrielle M. Miller1 • Sue-Ann Watson1,2 • Jodie L. Rummer1 Katharina Fabricius3 • Philip L. Munday1
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Received: 29 November 2019 / Accepted: 28 May 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract 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. Topic Editor Michael Lee Berumen
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00338-020-01973-z) contains supplementary material, which is available to authorised users. & Kelly D. Hannan [email protected] 1
ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia
2
Biodiversity and Geosciences Program, Museum of Tropical Queensland, Queensland Museum, Townsville, QLD 4810, Australia
3
Australian Institute of Marine Sciences, Townsville 4811, Australia
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 (D 250 latm) than the exposed (high flow) reefs (D 116 latm). 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. Keywords Reef metabolism Fluctuation pCO2 pH Coral reef Microhabitat
Introduction Anthropogenic activities are emitting steadily increasing amounts of carbon dioxide (CO2) into the atmosphere. As a result, the concentration of atmospheric CO2 has increased by over 45% during the industrial age, from approximately 280 ppm bef
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