Physiological responses to temperature and ocean acidification in tropical fleshy macroalgae with varying affinities for inorganic carbon. (13th December 2020) - Ho, Maureen
Abstract: Marine macroalgae have variable carbon-uptake strategies that complicate predicting responses to environmental changes. In seawater, dissolved inorganic carbon availability can affect the underlying physiological mechanisms influencing carbon uptake. We tested the interactive effects of ocean acidification (OA) and warming on two HCO 3 − -users ( Lobophora sp. and Amansia rhodantha ), a predominately CO2 -user ( Avrainvillea nigrican s), and a sole CO2 -user ( Plocamium hamatum ) in the Great Barrier Reef, Australia. We examined metabolic rates, growth, and carbon isotope values ( δ 13 C) in algae at 26, 28, or 30°C under ambient or elevated p CO2 (∼1000 µatm). Under OA, δ 13 C values for the HCO 3 − -users decreased, indicating less reliance on HCO 3 −, while δ 13 C values for CO2 -users were unaffected. Both HCO 3 − -users decreased in growth across temperatures under ambient p CO2, but this negative effect was alleviated by OA at 30°C. A. nigricans lost biomass across all treatments and P. hamatum was most sensitive, with reduced survival in all physiological responses. Metabolic rates varied greatly to interacting temperature and OA and indicated a decoupling between the relationship of photosynthesis and growth. Furthermore, our findings suggest HCO 3 − -users are more responsive to future CO2 changes, and highlight examining carbon physiology to infer potential responses to interacting environmental stressors.