The effect of CO2 enrichment on net photosynthesis of the red alga Furcellaria lumbricalis in a brackish water environment.

Liina Pajusalu,Arno Põllumäe,Tiina Paalme,Georg Martin

doi:10.7717/peerj.2505

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 CO2 concentration on the net photosynthesis of the red macroalgae Furcellaria 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 pCO2 levels: 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 pCO2 and different environmental factors exerted interactive effects on the photosynthetic rate of F. lumbricalis. In addition, laboratory experiments were carried out to determine the optimal temperature for photosynthesis of F. lumbricalis. The results of our field experiments demonstrated that elevated pCO2 levels may remarkably enhance the photosynthetic rate of F. lumbricalis. However, the magnitude of this effect is altered by different environmental factors, mainly by changes in water temperature.

Highlights

Ocean acidification is defined as a reduction in the global ocean pH, caused by the uptake of carbon dioxide (CO2) from the atmosphere (Caldeira & Wickett, 2003)
The study demonstrated that elevated water CO2 concentrations may enhance the photosynthetic rate of the red macroalga Furcellaria lumbricalis in the brackish Baltic Sea
In 2013 the increase in water temperatures resulted in the increase of net primary production (NP) rates at all pCO2 levels, while in 2012 the direction and size of the effect of water temperature on NP rates was dependent on pCO2 levels

Summary

Introduction

Ocean acidification is defined as a reduction in the global ocean pH, caused by the uptake of carbon dioxide (CO2) from the atmosphere (Caldeira & Wickett, 2003). Since the Industrial Revolution, the average surface ocean pH has fallen by ∼0.1 units and if global emissions of CO2 continue to rise, the pH may decrease 0.2–0.3 units by 2100 (IPCC, 2014). Scenario modelling suggests that the surface water pH in the central Baltic Sea may decrease 0.3–0.4 units by 2100 (Omstedt et al, 2012; Schneider et al, 2015). The Baltic Sea is sensitive to an increase in acidity due to low carbonate buffering capacity, which is related to its low salinity, in the northern parts (Omstedt et al, 2015).

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