VALIDATION OF THE ALKALINITY ANOMALY TECHNIQUE FOR INVESTIGATING CALCIFICATION AND PHOTOSYNTHESIS IN CORAL-REEF COMMUNITIES

Experiments were conducted to establish the validity of the alkalinity anomaly technique for investigating rates of calcification and photosynthesis by coral reef-building organisms. Rates of CaCO3 precipitation by whole colonies of the scleractinian coral Pocillopora damicornis (L.) were estimated under light and dark conditions with two different methods: complexometric titration of Ca with EGTA and acid titration of total alkalinity, with and without correction for alterations in the concentrations of ions other than carbonate species. The two techniques provided equivalent estimates of light-enhanced and dark calcification, irrespective of whether corrections were applied to the total alkalinity data for changes in nutrient concentration. These results confirm that the assumptions of the alkalinity anomaly technique are fundamentally correct and that it is not necessary to correct total alkalinity data for changes in nutrient concentration because the corrections which apply are smaller than the variability observed in calcification data.