Effects of elevated CO(2) on phytoplankton during a mesocosm experiment in the southern eutrophicated coastal water of China

There is a growing consensus that the ongoing increase in atmospheric CO(2) level will lead to a variety of effects on marine phytoplankton and ecosystems. However, the effects of CO(2) enrichment on eutrophic coastal waters are still unclear, as are the complex mechanisms coupled to the development of eutrophication. Here, we report the first mesocosm CO(2) perturbation study in a eutrophic subtropical bay during summer by investigating the effect of rising CO(2) on a model artificial community consisting of well-characterized cultured diatoms (Phaeodactylum tricornutum and Thalassiosira weissflogii) and prymnesiophytes (Emiliania huxleyi and Gephyrocapsa oceanica). These species were inoculated into triplicate 4 m(3) enclosures with equivalent chlorophyll a (Chl-a) under present and higher partial pressures of atmospheric CO(2) (pCO(2) = 400 and 1000 ppmv). Diatom bloom events were observed in all enclosures, with enhanced organic carbon production and Chl-a concentrations under high CO(2) treatments. Relative to the low CO(2) treatments, the consumption of the dissolved inorganic nitrogen and uptake ratios of N/P and N/Si increased significantly during the bloom. These observed responses suggest more extensive and complex effects of higher CO(2) concentrations on phytoplankton communities in coastal eutrophic environments.