Microcosm Investigations of Carbonate Reef Microbial Biogeochemistry

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Gaidos AbstractThis project is a one-year proof-of-concept project that is demonstrating the use of laboratory microcosm experiments to investigate the impact of elevated atmospheric CO2 levels and higher carbonate solubility on the microbial community and biogeochemistry of carbonate reefs. The research program is being carried out at the Hawaii Institute of Marine Biology in Kaneohe Bay. HIMB is the site of a long-term monitoring project that studies the dynamical interaction between estuarine and reef ecosystems in the bay. For this demonstration phase, the PIs are reconstructing the interior reef sediment and its heterotrophic microbial community; the system is being "fed" natural particulate organic matter from seawater. The objectives are to replicate the geochemical gradients observed in the natural reef system and generate preliminary data on the effect of elevated CO2 on reef hydraulics, carbonate mineralogy, porewater chemistry, and microbiology. Measurements include the hydraulic conductivity and changes in the bulk carbonate mineral fraction of the sediments. The structure and mineralogy of the carbonate framework is being studied using electron microscopy, X-ray diffraction and cathodoluminescence. Porewater analyses is measuring carbonate chemistry (pH, alkalinity, Mg2+ and Ca2+) and redox indicators (dissolved O2 and NH4+). Variation in the sediment microbial community along the sediment redox gradient is being monitored by direct counts and 16S rRNA phylotypes.