Short-term interactive effects of increased temperatures and acidification on the calcifying macroalgae Lithothamnion crispatum and Sonderophycus capensis

Combined effect of acidification and sea warming derived from future conditions of Climate Change have been little investigated in marine photoautotrophs, especially on sensitive organisms such as calcifying macroalgae. The aim of this investigation was to evaluate the interactive effects of acidification and increased temperatures on the two Brazilian calcifying macroalgae Lithothamnion crispatum and Sonderophycus capensis. Both species were cultured for 48 h under: (1) current pH (7.8 ± 0.2) and temperature (18 ± 2 °C) during winter; (2) future pH (7.4 ± 0.2) and temperature (30 ± 2 °C) during summer; (3) current temperature and future pH; and (4) future temperature and current pH. We evaluated photosynthetic performance (measured ΔF/F´m), growth rates (weight), relative carbonate content, and total phenolic compounds. Our results showed similar negative effects under decreased pH and increased temperatures in both species, although carbonate content S. capensis was less affected than in L. crispatum. Total phenolic compounds measured in S. capensis showed the highest levels at potential future pH and temperature conditions. Given that stress conditions associated with decreased pH and increased temperatures are important inductors of an oxidative response, it is likely that phenolic compounds are synthetized to fulfil an antioxidant purpose. Even though physiological performance was affected in both calcifying macroalgae under the most likely negative future pH and temperature conditions, their biological viability indicates they may be able to thrive under coming Climate Change scenarios.