An automated pH-controlled culture system for laboratory-based ocean acidification experiments

Christina M. McGraw, Christopher E. Cornwall, Malcolm R. Reid, Kim I. Currie, Christopher D. Hepburn, Philip Boyd, Catriona L. Hurd, and Keith A. Hunter

Limnol. Oceanogr. Methods 8:686-694 (2010) | DOI: 10.4319/lom.2010.8.0686

ABSTRACT: Using a spectrophotometric pH measurement system, an automated 12-tank culture system was developed, which is capable of maintaining pH levels between 7.51 and 8.00 (local, in-situ pH) within 0.02 pH units at 15.1°C. The precise control of pH in the individual culture tanks was achieved through the addition of CO2-enriched seawater to unamended seawater. A feed-back system, which automatically adjusted the mixing ratio of unamended and CO2-enriched seawater, ensured that the pH in each tank was kept within 0.02 pH units of target values. After each tank adjustment, the spectrophotometric pH measurement was combined with a dissolved inorganic carbon measurement to automatically re-calculate carbonate chemistry in each tank. The system was used to study the growth of the geniculate coralline alga Arthrocardia corymbosa at pH levels of 7.52, 7.76, and 7.98.