Physiological responses of Caulerpa spp. (with different dissolved inorganic carbon physiologies) to ocean acidification

• Published in: New Zealand Journal of Botany
• Main Authors: Taise, Aleluia, Krieger, Erik, Bury, Sarah J., Cornwall, Christopher E.
• Other Authors: Marine Science Program, Biological and Environmental Science and Engineering (BESE) Division, Red Sea Research Center (RSRC), School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand, Department of Science, Faculty of Science, National University of Samoa, Apia, Samoa, National Institute of Water & Atmospheric Research Ltd (NIWA), Wellington, New Zealand
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Informa UK Limited 2023
• Subjects: Ocean acidification
• Online Access: http://hdl.handle.net/10754/696125; https://doi.org/10.1080/0028825x.2023.2289432

Caulerpa is a widely distributed genus of chlorophytes (green macroalgae) which are important for their dietary, social and coastal ecosystem value. Ocean acidification (OA) threatens the future of marine ecosystems, favouring macroalgal species that could benefit from increased seawater carbon dioxide (CO2) concentrations. Most macroalgae species possess CO2 concentrating mechanisms (CCMs) that allow active uptake of bicarbonate (HCO3−). Those species without CCMs are restricted to using CO2, which is currently the least abundant species of dissolved inorganic carbon (DIC) in seawater. Thus, macroalgae without CCMs are predicted to be likely benefit from OA. Caulerpa is one of the rare few genera that have species both with and without CCMs. The two most common Caulerpa species in New Zealand are C. geminata (possesses a CCM) and C. brownii (non-CCM). We investigated the responses of growth, photo-physiology and DIC utilisation of C. geminata and C. brownii to four mean seawater pH treatments (8.03, 7.93, 7.83 and 7.63) that correspond to changes in pH driven by increases in pCO2 simulating future OA. There was a tendency for the mean growth rates for C. brownii (non-CCM) to increase under lower pH, and the growth rates of C. geminata (CCM) to decline with lower pH, although this was not statistically significant. However, this is likely because variability in growth rates also increased as seawater pH declined. There were few other differences in physiology of both species with pH, although there was tendency for greater preference for CO2 over HCO3− uptake in the CCM species with declining seawater pH. This study demonstrates that DIC-use alone does not predict macroalgal responses to OA. We thank Julie Brown, Josette Delgado, Graeme Moss, Andrew Marriner and Antonia Cristi of NIWA, Wellington, for the stable isotope analysis of samples, and Professor Giuseppe C. Zuccarello of Victoria University of Wellington, for guidance.