Quantifying the potential for biogeochemical feedbacks to create 'refugia' from ocean acidification on tropical coral reefs

Rising sea surface temperatures and ocean acidification (OA) may threaten the ability of calcified organisms to build carbonate reefs, but it is unclear if particular reefs have the capacity to tolerate global change. Current understanding of the effects of OA on coral reefs originates from single-species laboratory studies largely focused on scleractinian corals. Traditionally, these experiments attempt to mimic static future conditions under the assumption that coastal regimes are as constant as -- and will acidify at the same rate as -- open ocean surface waters. Predictions based on these oversimplified scenarios are unrealistic because numerous benthic organisms, including calcifiers and primary producers, significantly alter the bulk seawater carbonate chemistry over a diurnal cycle. Further, the prevalence of recently appreciated extreme diel fluctuations in pH across some reefs suggests that benthic species may be acclimated to future carbonate conditions. To look for potential OA refugia on reefs, a research team from the Scripps Institute of Oceanography (University of California at San Diego) and the Lamont Dougherty Earth Observatory (Columbia University) will undertake a unique mechanistic study on Palmyra Atoll, a remote uninhabited island in the central Pacific that lacks degradation from local human influence. They will explore the strengths and controls of biogeochemical feedbacks from coral reef benthic community assemblages to the seawater chemistry above and experimentally determine how this natural fluctuation affects physiological responses of key taxa to OA. Specifically they will: (1) tightly integrate a novel benthic flux technique in situ that allows continuous, high-temporal resolution measurements of net ecosystem metabolic rates (production and calcification) with an ongoing high spatial resolution benthic community dynamics study to quantify feedbacks of known species assemblages to observed natural spatiotemporal variability in seawater carbonate chemistry; and (2) use small scale common garden CO2 enrichment experiments and productivity/respiration assays in the lab paired with reciprocal transplant experiments in situ to empirically quantify the effects of elevated and/or fluctuating pCO2 on growth, calcification and photophysiology of common framework building organisms and their benthic competitors. This should allow them to examine the coupled interactions between OA and diverse benthic coral reef organisms in their natural environment in the absence of other confounding human impacts. BROADER IMPACTS. Ocean acidification is expected to affect a number of ecosystem goods and services that human societies have come to depend on. Specifically, the physical protection that coral reefs provide from coastal erosion will be reduced, potentially exacerbating the effects of sea level rise, and the effects of OA on fisheries and tourism are yet to be determined. One central goal is to work with local communities and organizations to better educate the public about how OA will affect people, societies and the natural resources they use and to give individuals tools that can allow them to be part of the solution. To that end, the research team has established strong partnerships with a local non-profit public broadcasting service KPBS, San Diego to develop novel products for OA communication and education. Further, they will work with the Birch Aquarium at SIO to develop an exhibit that communicates the results of the project. Finally, the project will directly train interns, students and researchers and will promote diversity through a variety of outreach activities including public lectures, training of aquarium docents and the development of web-based educational materials.