Abstract: Ocean acidification is projected to shift coral reefs from a state of net accretion to one of net dissolution this century. Presently, our ability to predict global-scale changes to coral reef calcification is limited by insufficient data relating seawater carbonate chemistry parameters to in situ rates of reef calcification. Here, we investigate natural trends in carbonate chemistry of the Davies Reef flat in the central Great Barrier Reef on diel and seasonal timescales and relate these trends to benthic carbon fluxes by quantifying net ecosystem calcification (nec) and net community production (ncp). Results show that seawater carbonate chemistry of the Davies Reef flat is highly variable over both diel and seasonal timescales. pH (total scale) ranged from 7.92 to 8.17, pCO2 ranged from 272 to 542 µatm, and aragonite saturation state (Ωarag) ranged from 2.9 to 4.1. Diel cycles in carbonate chemistry were primarily driven by ncp. Net ecosystem calcification was positively correlated with Ωarag for both seasons. Linear correlations of nec and Ωarag indicate that the Davies Reef flat may transition from a state of net calcification to net dissolution at Ωarag values of 3.4 in summer and 3.2 in winter. Diel trends in Ωarag indicate that the reef flat is currently below this calcification threshold 29.6% of the time in summer and 14.1% of the time in winter.

Biography: Rebecca received a Bachelor of Science from Duke University in 2003 and a Ph.D. from the Rosenstiel School of Marine and Atmospheric Science, University of Miami in 2011. She is currently a Super Science Fellow at the Australian Institute of Marine Science. The overarching goal of her research is to assess ecosystem response to changing environmental conditions. She has devoted the last 8 years to investigating the effects of ocean acidification on coral reef ecosystems. During this time, she has developed and led a variety of projects that address this central question at various scales ranging from single cells (gamete interactions and fertilization success) to individual organisms (perturbation experiments investigating the effects of ocean acidification on corals, calcareous algae, gorgonians, and sea urchins) and whole-reef processes (net ecosystem calcification and production). Currently, her research addresses two main questions: 1) how benthic carbon flux processes influence ocean acidification impacts on coral reefs; and 2) how ocean acidification will impact coral reproduction and recruitment.

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