|  |
Program |
 |
| |
 |
Special Session 1: Ecosystem under multiple stressors |
| |
|
|
Marine primary producers under influence of ocean acidifcation
SS1-05
Kunshan Gao* , Xiamen University
Presenter Email: ksgao@xmu.edu.cn
|
| The oceans are taking up over one million tons of CO2 per hr, but, have been acidified by 30% since the industrial revolution, and will be further acidified by 150% (pH drop to 7.8, IPCC A1F1 scenario) by the end of this century. Typical chemical changes associated with the ocean acidification (OA) are increased concentrations of pCO2¡¢H+ and HCO3- and decreased concentration of CO32- and CaCO3 saturation state, with different extents in different regions or waters. On the other hand, decreasing thickness of upper mixing layer, caused by global warming, leads to increased exposures of phytoplankton cells to UV radiation. Marine photosynthetic and heterotrophic are being affected by the global ocean changes (Riebesell and Gattuso 2015) 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. 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. In addition, photorespiration and mitochondrial respiratory carbon loss were also enhanced. Future ocean warming will cause a shoaling of upper mixed layer depths, exposing phytoplankton to increased mean light intensities. This, in combination with rising CO2 levels, may cause a widespread decline in marine primary production (Gao et al. 2012). Based on the data obtained from micro- and mesocosm experiments, OA has been shown to increase 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 (Jin et al. 2015). While UV irradiances, depending there incident levels, can lead to inhibitive, neutral or stimulating effects on marine photosynthesis, combined effects of UV and OA treatment resulted in inhibition of calcification rates and that of photosynthesis, respectively, in calcifying algae. These results, also supported from shipboard experiments in the South China Sea, imply that calcifying algae may suffer from more damages caused by UVB when they calcify less and less with progressing ocean acidification (Xu and Gao 2015). |
|
|
|
|