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Marine pollution, ecotoxicology and sustainability
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Marine Photosynthetic organisms under influence of ocean acidification
Monday 7th @ 0950-1010, Conference Room 7
Kunshan Gao* , Xiamen Univ
Presenter Email: ksgao@xmu.edu.cn |
| The oceans are taking up over one million tons of fossil fuel CO2 per hr, and consequently have been acidified by 30% since the industrial revolution, and will be further acidified by 150% (IPCC A1F1 scenario) by the end of this century. Typical chemical changes associated with the ocean acidification (OA) are increased concentrations of pCO2 + and HCO3- and decreased concentration of CO32- and CaCO3 saturation state, with different extents in different regions.
When exposed to CO2 concentrations projected for the end of this century, natural phytoplankton assemblages in the upper surface layer of the South China Sea (SCS) responded with decreased photosynthetic carbon fixation and increased non-photochemical quenching (NPQ). The community composition of these experimental phytoplankton assemblages shifted away from diatoms, the dominant phytoplankton group encountered during our field campaigns. Meanwhile, when diatom species were grown at different CO2 concentrations under varying levels (5-100%) of solar radiation, above 22-36% of incident surface solar radiation, corresponding to 26-39 m depths in the SCS, growth rates in the high CO2-grown cells were inversely related to light levels, and exhibited reduced thresholds at which PAR becomes excessive, leading to higher NPQ. That is, elevated CO2 concentrations (lowered pH) impaired the specific growth rate of diatoms at high levels, but enhanced it at low to moderate levels of solar irradiances. These puzzling results are explained as follows: elevated CO2 concentrations down-regulate the uptake capacity (CO2 concentrating mechanisms) of the cells for dissolved inorganic carbon, so that energy, which is used for the active uptake mechanism, is saved and the diatoms growth at low irradiances is augmented; on the other hand, at high levels of solar radiation, the saved light energy could add to enhance photorespiration and photoinhibition, result in reduced growth rate and enhanced NPQ.
Additionally, based on the data obtained from micro- and mesocosm experiments, OA increases contents of phenolic compounds in phytoplankton and in zooplankton assemblages fed with OA-grown phytoplankton cells. The observed accumulation of the toxic phenolic compounds in primary and secondary producers can have profound consequences for marine ecosystem and seafood quality, with a possibility that fisheries industries could be influenced due to progressive ocean changes.
In terms of combined effects of OA with solar UV irradiances, we found that calcified keleton of calcifying micro- and macro-algae plays a protective role against harmful solar UV radiation. Under OA conditions, these algae calcify less and less under the acidic stress and lowered saturation state of CaCO3. When exposed to solar radiation, OA treatment acted with solar UV radiation synergistically to inhibit rates of calcification and photosynthesis. These results, also supported from shipboard experiments in the South China Sea, imply that calcifying algae suffer from more damages caused by UVB with progressing ocean acidification.
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