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

The impact of elevated C[O.sub.2] 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°C) and pC[O.sub.2] (400, 1,000 µatm) levels spanning a range of current and future climate-change scenarios. The photosynthetic capacity of M. vertebralis was measured with [O.sub.2] microsensors and a pulse-amplitudemodulated chlorophyll (Chl) fluorometer, in combination with estimates of Chl a and Chl [c.sub.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 µatm C[O.sub.2] for both temperatures, while no change in Chl [c.sub.2] concentration was observed. Photoinhibition was observed under elevated C[O.sub.2] and temperature, with a 70-80 % decrease in the maximum quantum yield of PSII. There was no net [O.sub.2] production at elevated temperatures in both C[O.sub.2] treatments as compared to the control temperature, supporting that temperature has more impact on photosynthesis and [O.sub.2] flux than changes in ambient C[O.sub.2]. Photosynthetic pigment loss and a decrease in photochemical efficiency are thus likely to occur with increased temperature. The elevated C[O.sub.2] and high temperature treatment also lead to a reduction in calcification rate (from +0.1 to >-0.1 % [day.sup.-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.
Introduction Climate change is expected to have significant impacts on near-shore marine ecosystems and their resident organisms (Johnson and Marshall 2007). Human activities, such as burning of fossil fuels, industrialization, [...]