1. Ocean Acidification

2. Just some facts • CO2 concentrations: preindustrial 280 ppmv 2007 385 ppmv (40% increase) • pH of ocean: preindustrial 8.21 2005 8.10 • pH is expected to drop 0.3-0.4 units at the turn of the century when CO2 levels are expected to be 800 ppmv (IPCC)

3. How does increased atmospheric CO2 decrease ocean pH? • Air-sea gas exchanges equilibrates surface water CO2 in approximately 1 year • Increased aqueous CO2 increases bicarbonate (HCO3-), and H+ • Increased H+ lowers carbonate ion (CO32-) and pH (pH=-log10[H+]) • CO2(aq) + H2O↔H2CO3↔H+ + HCO3-↔ 2H+ + CO32-

5. Calcifying organisms • Plankton, corals, and coralline algae use CaCO3 to form shells and skeletons • When CO32- concentration is decreased the saturation state decreases restricting the ability of CaCO3 (or shell) formation • Dissolution rates increase as well

6. Planktonic Calcification • Major groups: coccolithophores and foraminifera • Coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica showed a 25-66% decrease in calcification when CO2 was 560-840μatm respectively • Calcidiscus leptoporus also showed a decrease in calcification rates as well as increased malformations in response to increased pCO2

7. Planktonic Calcification • Symbiot-bearing, planktonic foraminifera, had a decrease in shell mass with increased concentration of carbonate ion • Orbulina universa and Globigerinoides sacculifer experienced a 4-6% and 6-14% decline in shell mass when exposed to 560 and 740 ppmv CO2 when compared to preindustrial CO2 levels

8. Impacts on corals • Coral bleaching: the loss of color in corals, due to stress-induced expulsion of symbiotic unicellular algae or due to the loss of pigmentation within the algae • Anthony et al. exposed three coral species to three different CO2 levels at low and high temperatures to determine effect on bleaching

10. Impact on corals • High CO2 dosing (1000-1300 ppm) led to 40-50% bleaching in crutose coralline algae (CCA) and Acropora • Intermediate CO2 dosing (520-700 ppm) led to 30% and 20% bleaching in CCA and Acropora • Present day CO2 (380 ppm) led to a 20% and 10% bleaching in CCA and Acropora

11. Impacts on corals • Effect of CO2 dosing on bleaching had a stronger effect than that of temperature • High CO2 had a two to threefold increase in bleaching and temperature had only a 20% increase in bleaching • Lowered pH disrupts photoprotective mechanisms of symbiots by lowering rates of photorespiration and capacity for thermal dissipation

13. Why this matters • Corals responsible for high amount of productivity and bleaching results in loss of productivity • Disruption in ability to make shells may lower abundance of algae • Loss of major food source or community shifts

14. References • Anthony, K. 2008. Ocean acidification causes bleaching and productivity loss in coral reef builders. Enviromental Sciences. 105:17442-17446. • Doney, S. 2009. Ocean acidification: The other CO2 problem. Annu. Rev. Marine. Sci. 1:169-192. • Orr, J. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature. 437:681-686.