ADAPTATION OF AUTONOMOUS SENSORS TO EVALUATE A MESOCOSM SETUP FOR EXAMINING HAWAIIAN CORALS UNDER VARIOUS CHEMICAL PERTERBATIONS

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2024

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Marine ecosystems, such as coral reefs, are sustained by positive net community calcification, but calcification is impeded by Ocean Acidification (OA), which alters ocean chemistry and disrupts the ability of calcifying organisms to maintain their calcium carbonate skeletons. Mesocosm experiments were performed at the Hawai’i Institute of Marine Biology in Kāneʻohe Bay, Oʻahu to investigate if calcification is limited by carbonate ions or waste protons from calcification. These studies often involve labor-intensive discrete measurements, which can be limited in sample number and often require a long bench time to analyze (15 - 30 minutes). In response to this challenge, two low-cost waterproof housings of the autonomous Honeywell Durafet® pH sensor were created and deployed in mesocosm tanks from June to August of 2023 to (1) quantify spatial variability of pH in tanks under OA simulated and ambient conditions, and (2) to evaluate predictors of Net Community Calcification (Gnet) in tanks under three different OA scenario treatments, coupling elevated pCO2 with high, low or ambient Total Alkalinity (AT). To evaluate spatial variability in the tanks, high frequency pH measurements (~20 sec) were made every 17.78 centimeters (seven inches) around the tank perimeter at top, middle and bottom depths. Spatial measurements showed that tanks were not chemically homogenous as pH and corals were driving benthic patterns in the tank. Furthermore, autonomous measurements and discrete samples (taken via an automatic sampler) of bulk mesocosm seawater showed that major independent predictors of Gnet in treatments of high and low AT and high pCO2 were the aragonite saturation state (Ωa) and Net Community Production (Pnet). The work presented here provides detailed information about mesocosm tank dynamics and coral response that will be useful for future mesocosm experiments.

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Geochemistry, Hawaiian corals, Ocean acidification, sensor adaptation

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64 pages

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