Ocean Acidification: Controls on Reef pH
Principal Investigator: Dr. Chris Martens, UNC Chapel Hill
Knowledge of the present and potential future threats of ocean acidification to coral reef ecosystems is critical to planning for their preservation and mitigating damage associated with global-scale pH changes. Can we accurately monitor pH and the carbonate system in coral reef environments? How can pH variability and changes in the carbonate system resulting from global-scale change be differentiated from higher frequency shifts resulting from local-scale processes occurring immediately adjacent to corals and other important calcifiers? Our research team, including marine chemists, coral reef ecologists, and physical oceanographers, is focused on obtaining accurate measures of how near-bottom benthic boundary layer (BBL) respiration processes interact with global ocean acidification to impact coral reef calcification rates. Focusing on the lower regions of the BBL where water quality parameters and chemical characteristics are dominated by local processes and slow diffusion rather than rapid advective mixing will be critical for understanding the impact of pH on calcification rates of corals because their recovery through the survival and growth of young recruits residing within the region of the BBL must occur from the bottom-up. Changes in the total dissolved inorganic carbon (ΣCO2), carbonate alkalinity (CA), CO2 fugacity (pCO2) and pH in the near-bottom BBL involves complex interactions of sources and sinks dominated by daily cycles of photosynthetic processes of benthic seaweeds and cynaobacteria versus the nearly constant, high respiration of sponges. Our new, Aquarius- or surface ship-tested instrumentation provides a unique opportunity to conduct in situ measurements of carbonate system and pH values with state-of-the-art precision. Knowledge of the in situ rates of benthic respiration processes and their impact on local pH has been virtually non-existent but is likely of substantial importance given the great abundance and biomass of sponges on Florida and Caribbean coral reefs and their high metabolic rates. In addition, the impacts of increasing macroalgal and cyanobacterial mat biomass needs to be investigated. Coral reef managers need to be aware of a distinction between pH changes associated with global-scale ocean acidification and local sponge- or algal mat mediated changes so as to implement effective strategies for mitigating impacts.