Characterizing the response of coralline algae to ocean acidification and nutrient changes in the California Current system (MSc thesis)

Ocean acidification (OA) has emerged as an important focus of research and policy in this decade. Ocean acidification specifically refers to changes in the inorganic carbon system in the ocean resulting from its absorption of human-released CO₂ from the atmosphere. Anthropogenic atmospheric CO₂ levels are rapidly increasing; much of this is dissolved and absorbed in the ocean (~30%) where it reacts with seawater altering fundamental properties including pH, pCO₂ and saturation state of carbonate minerals. This change is of concern because of the potential of OA to disrupt biological processes, particularly those processes associated with calcification (Byrne, 2011; Diaz-Pilido, Anthony, Kline, Dove, & Hoegh-Guldberg, 2012). For this study, I chose to investigate red coralline algae as a model organism because OA is predicted to have effects on calcification and photosynthesis, and because of the importance of coralline algae as an ecological engineer, which can be found in shallow water habitats globally. While the response of coralline algae to OA is a serious concern, there remains very limited data on the interactions of OA with other ocean conditions (e.g., temperature, nutrients, and light) that may alter or modify the effects of low pH on coralline algae communities. One nutrient in particular, phosphorus is known to have inhibiting effects on calcification in long-term studies. My objective was to describe the short-term effects of a range of elevated pCO₂ and phosphorus levels both alone, and together, on calcification and photosynthetic rates of Corallina vancouveriensis. I exposed these algae to a range of pCO₂ and phosphate concentrations and measured changes in total alkalinity, pH, and DO in acute exposure trials (<3 hours). Corallina calcification rates were negatively affected by elevated pCO₂ levels and decreased proportionately across a range of pCO₂ from 300 to 2500 μatm. In contrast, exposure to elevated levels phosphate had no effect on Corallina calcification or photosynthesis. When exposed to both elevated levels of phosphate and pCO₂ together, I found no evidence of interactions between these factors. The results suggest that future atmospheric CO₂ levels will have an impact on the calcification rates of Corallina, and that these rates will not be influenced acutely by increasing levels of phosphate found in coastal oceans.

Letzing S., 2013. Characterizing the response of coralline algae to ocean acidification and nutrient changes in the California Current system. MSc thesis, Oregon State University, 51p. MSc thesis.

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