The combined effects of pH and temperature on the physiology of the temperate coral Oculina arbuscula

The purpose of this investigation was to investigate the impact of ocean acidification and warming sea temperature on Oculina arbuscula, a temperate scleractinian coral found in Gray’s Reef National Marine Sanctuary (GRNMS) off the coast of Sapelo Island, GA. GRNMS experiences seasonal fluctuations in temperatures that reach 30°C and concurrent decreases in pH to approximately 8.0, thus naturally modelling the projected effects of anthropogenic climate change on an annual basis. Oculina arbuscula colonies in GRNMS are exposed to these natural fluctuations in temperature and pH, therefore I hypothesized that this species is resistant to the combined effects of high temperature and low pH. Specifically, I predicted that there would be no effects on calcification rates, symbiont densities, or chlorophyll a concentrations. To test these predictions, O. arbuscula colonies were collected from GRNMS, divided into three treatments and a control, and maintained for 75 days. Ambient temperature was applied at 26°C while high temperature was 31°C, and the ambient pH was 7.9 with a low pH of 7.65. The ambient values were applied to the control aquaria, and the three treatments experienced ocean acidification (ambient temperature, low pH), ocean warming (high temperature, ambient pH), and combined ocean warming and acidification (high temperature, low pH). Results showed that calcification rates were significantly reduced by the combined stressors and symbiont densities and chlorophyll concentrations were significantly reduced by high temperature treatments. These results indicated that with continued ocean acidification and warming, the success of Oculina arbsucula within the spatially competitive benthic communities in GRNMS may be compromised.

Rogers S. H., 2019. The combined effects of pH and temperature on the physiology of the temperate coral Oculina arbuscula. BSc thesis, Georgia Southern University. Article (restricted access).

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