Ocean acidification and warming alter photosynthesis and calcification of the symbiont-bearing foraminifera Marginopora vertebralis

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Journal Article
Marine Biology, 2014, 161 (9), pp. 2143 - 2154
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The impact of elevated CO2and temperature on photosynthesis and calcification in the symbiont-bearing benthic foraminifer Marginopora vertebralis was studied. Individual specimens of M. vertebralis were collected from Heron Island on the southern Great Barrier Reef (Australia). They were maintained for 5 weeks at different temperatures (28, 32 °C) and pCO2(400, 1,000 μatm) levels spanning a range of current and future climate-change scenarios. The photosynthetic capacity of M. vertebralis was measured with O2microsensors and a pulse-amplitude-modulated chlorophyll (Chl) fluorometer, in combination with estimates of Chl a and Chl c2concentrations and calcification rates. After 5 weeks, control specimens remained unaltered for all parameters. Chlorophyll a concentrations significantly decreased in the specimens at 1,000 μatm CO2for both temperatures, while no change in Chl c2concentration was observed. Photoinhibition was observed under elevated CO2and temperature, with a 70-80 % decrease in the maximum quantum yield of PSII. There was no net O2production at elevated temperatures in both CO2treatments as compared to the control temperature, supporting that temperature has more impact on photosynthesis and O2flux than changes in ambient CO2. Photosynthetic pigment loss and a decrease in photochemical efficiency are thus likely to occur with increased temperature. The elevated CO2and high temperature treatment also lead to a reduction in calcification rate (from +0.1 to >-0.1 % day-1). Thus, both calcification and photosynthesis of the major sediment-producing foraminifer M. vertebralis appears highly vulnerable to elevated temperature and ocean acidification scenarios predicted in climate-change models. © 2014 Springer-Verlag Berlin Heidelberg.
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