Testing the effects of ocean acidification on algal metabolism: considerations for experimental designs

• Published in: Journal of Phycology
• Main Authors: Hurd, CL, Currie, K, Raven, J, Hunter, K, Hepburn, D
• Format: Article in Journal/Newspaper
• Language: English
• Published: Blackwell Publishing Inc 2009
• Subjects: Environmental Sciences; Ecological Applications; Ecological Impacts of Climate Change; Ocean acidification
• Online Access: https://doi.org/10.1111/j.1529-8817.2009.00768.x; http://ecite.utas.edu.au/91479

Ocean acidification describes changes in the carbonatechemistry of the ocean due to the increasedabsorption of anthropogenically released CO2.Experiments to elucidate the biological effects ofocean acidification on algae are not straightforwardbecause when pH is altered, the carbon speciationin seawater is altered, which has implications forphotosynthesis and, for calcifying algae, calcification.Furthermore, photosynthesis, respiration, andcalcification will themselves alter the pH of the seawatermedium. In this review, algal physiologistsand seawater carbonate chemists combine theirknowledge to provide the fundamental informationon carbon physiology and seawater carbonate chemistryrequired to comprehend the complexities ofhow ocean acidification might affect algae metabolism.A wide range in responses of algae to oceanacidification has been observed, which may beexplained by differences in algal physiology, timescalesof the responses measured, study duration,and the method employed to alter pH. Two methodshave been widely used in a range of experimentalsystems: CO2 bubbling and HCl ⁄NaOHadditions. These methods affect the speciation ofcarbonate ions in the culture medium differently; wediscuss how this could influence the biologicalresponses of algae and suggest a third method basedon HCl ⁄NaHCO3 additions. We then discuss eightkey points that should be considered prior to settingup experiments, including which method of manipulatingpH to choose, monitoring during experiments,techniques for adding acidified seawater, biological side effects, and other environmental factors. Finally,we consider incubation timescales and prior conditioningof algae in terms of regulation, acclimation,and adaptation to ocean acidification.Key index words: algae; bicarbonate; calcium carbonate;carbon; carbon dioxide; climate change;ocean acidification; phytoplankton; seawater carbonatesystem; seaweedAbbreviations: AT, total alkalinity; CA, carbonicanhydrase; CCM, carbon-concentrating mechanism;CT, total inorganic carbon; pCO2, partialpressure of CO2(g)