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

The impact of elevated CO2 and 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 A degrees C) and pCO(2) (400, 1,000 A mu atm) levels spanning a range of current and future climate-change scenarios. The photosynthetic capacity of M. vertebralis was measured with O-2 microsensors and a pulse-amplitude-modulated chlorophyll (Chl) fluorometer, in combination with estimates of Chl a and Chl c (2) concentrations and calcification rates. After 5 weeks, control specimens remained unaltered for all parameters. Chlorophyll a concentrations significantly decreased in the specimens at 1,000 A mu atm CO2 for both temperatures, while no change in Chl c (2) concentration was observed. Photoinhibition was observed under elevated CO2 and temperature, with a 70-80 % decrease in the maximum quantum yield of PSII. There was no net O-2 production at elevated temperatures in both CO2 treatments as compared to the control temperature, supporting that temperature has more impact on photosynthesis and O-2 flux than changes in ambient CO2. Photosynthetic pigment loss and a decrease in photochemical efficiency are thus likely to occur with increased temperature. The elevated CO2 and 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.