In March 2011and June 2012, recruits were incubated at 31, 41, 70, 122 and 226 µmol photons m-2 s-1 under ambient (493 µatm) and high PCO2 (878 µatm). After 5 days, calcification was measured gravimetrically and survivorship estimated as the number of living recruits.
Total alkalinity (TA) and pH were measured following standard operating procedure (SOP) 3b and 6b (respectively) (see Dickson et al., 2007). TA was measured using an open cell automatic titrator (Model DS50, Mettler-Toledo, Columbus, OH, USA) filled with certified HCl titrant supplied by Dr A. Dickson (Scripps Institute of Oceanography), and TA was calculated using an Excel spreadsheet (Fangue et al., 2010). The accuracy and precision of the TA measurements were tested against certified reference material (CRM, from Dr A. Dickson) and maintained within 0.7% of certified values. pH was measured on the total scale (±0.001 pH) using m-Cresol Purple dye in a spectrophotometric assay (SOP 6b). TA and pH were used to calculate PCO2, [HCO3-], [CO3 =] and aragonite saturation state (OA) using CO2SYS (Pierrot et al., 2006).
References:
Dickson, A. G., Sabine, C. L. and Christian, J. R. (ed.) (2007). Guide to Best Practices for Ocean CO2 Measurements: PICES Special Publication 3. Sidney, BC: North Pacific Marine Science Organization.
Fangue, N., O'Donnell, M. J., Sewell, M. A., Matson, P. G., MacPherson, A. C. and Hofmann, G. E. (2010). A laboratory-based, experimental system for the study of ocean acidification effects on marine invertebrate larvae. Limnol. Oceanogr. Methods 8, 441-452.
Pierrot, D., Lewis, E. and Wallace, D. W. R. (2006). MS Excel Program Developed for CO2 System Calculations. ORNL/CDIAC-105a. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, TN: US Department of Energy.
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