The effect of CO2enrichment on net photosynthesis of the red algaFurcellaria lumbricalisin a brackish water environment

Abstract

Anthropogenic carbon dioxide (CO2) emissions to the atmosphere are causing reduction in the global ocean pH, also known as ocean acidification. This change alters the equilibrium of different forms of dissolved inorganic carbon in seawater that macroalgae use for their photosynthesis. In the Baltic Sea, benthic macroalgae live in a highly variable environment caused by seasonality and rapid changes in meteorological conditions. The effect of increasing water CO2concentration on the net photosynthesis of the red macroalgaeFurcellaria lumbricalis(Hudson) Lamouroux was tested in short-term mesocosm experiments conducted in Kõiguste Bay (N Gulf of Riga) in June–July 2012 and 2013. Separate mesocosms were maintained at different pCO2levels: ca. 2,000, ca. 1,000 and ca. 200 µatm. In parallel, different environmental factors were measured such as nutrients, light and water temperature. Thus, the current study also investigated whether elevated pCO2and different environmental factors exerted interactive effects on the photosynthetic rate ofF. lumbricalis. In addition, laboratory experiments were carried out to determine the optimal temperature for photosynthesis ofF. lumbricalis. The results of our field experiments demonstrated that elevated pCO2levels may remarkably enhance the photosynthetic rate ofF. lumbricalis. However, the magnitude of this effect is altered by different environmental factors, mainly by changes in water temperature.