Ocean acidification affects physiology of coccolithophore Emiliania huxleyi and weakens its mechanical resistance to copepods

The effects of ocean acidification (OA) on coccolithophore's photosynthesis, calcification rates, and growth have been extensively studied. However, how the intracellular Ca2+, mechanical properties and chemical composition of the coccoliths are affected by OA have not yet been investigated. This study tries to fill these gaps using Emiliania huxleyi as a model coccolithophore. When the seawater pCO2 increased from 400 mu atm to 1200 mu atm, the intracellular Ca2+ and coccolith area were reduced by 66% and 36%, respectively. Single-cell mapping by atomic force microscopy revealed that the modulus and hardness of coccolith decreased from 23.6 +/- 0.2 GPa to 12.0 +/- 5.5 GPa and from 0.53 +/- 0.15 GPa to 0.20 +/- 0.06 GPa, respectively. Additionally, the proportional organic matter and silicon in the coccolith surfaces increased with pCO2. The copepods Acartia pacifica fed on more E. huxleyi grown at higher pCO2. Our study implies that OA could change coccolithophore's competitive interactions with other phytoplankton and ultimately influence carbon export to the deep ocean.