Ocean Acidification Affects the Response of the Coastal Coccolithophore Pleurochrysis carterae to Irradiance

SIMPLE SUMMARY: Here, we investigated the response of the coccolithophore Pleurochrysis carterae (P. carterae) isolated from the Bohai Sea to ocean acidification under different irradiance levels. A full factorial matrix of two pCO(2) conditions (400 ppm and 800 ppm) and irradiance levels of 50, 200, 500 and 800 μmol photons m(−2) s(−1) were examined. The results suggest that ocean acidification suppressed the photosynthesis and increased the saturation irradiance for growth of the coccolithophore Pleurochrysis carterae. Further comparison with previously published results reveals that the physiological processes of the coastal coccolithophore specie Pleurochrysis carterae are less sensitive to ocean acidification than the smaller-sized species Emiliania huxleyi and Gephyrocapsa oceanica, and the saturation irradiance for the growth, particulate organic carbon (POC) and particulate inorganic carbon (PIC) production of Pleurochrysis carterae are much lower than those of the other two species. ABSTRACT: The ecologically important marine phytoplankton group coccolithophores have a global distribution. The impacts of ocean acidification on the cosmopolitan species Emiliania huxleyi have received much attention and have been intensively studied. However, the species-specific responses of coccolithophores and how these responses will be regulated by other environmental drivers are still largely unknown. To examine the interactive effects of irradiance and ocean acidification on the physiology of the coastal coccolithophore species Pleurochrysis carterae, we carried out a semi-continuous incubation experiment under a range of irradiances (50, 200, 500, 800 μmol photons m(−2) s(−1)) at two CO(2) concentration conditions of 400 and 800 ppm. The results suggest that the saturation irradiance for the growth rate was higher at an elevated CO(2) concentration. Ocean acidification weakened the particulate organic carbon (POC) production of Pleurochrysis carterae and the inhibition rate was decreased with increasing irradiance, indicating that ocean acidification may affect the tolerating capacity of photosynthesis to higher irradiance. Our results further provide new insight into the species-specific responses of coccolithophores to the projected ocean acidification under different irradiance scenarios in the changing marine environment.