Impact of low pH/high pCO2 on the physiological response and fatty acid content in diatom Skeletonema pseudocostatum

p CO 2 /pH perturbation experiments were carried out under two different p CO 2 levels to evaluate effects of CO 2 -driven ocean acidification on semi-continuous cultures of the marine diatom Skeletonema pseudocostatum CSA48. Under higher p CO 2 /lowered pH conditions, our results showed that CO 2 -driven acidification had no significant impact on growth rate, chlorophyll- a , cellular abundance, gross photosynthesis, dark respiration, particulate organic carbon and particulate organic nitrogen between CO 2 -treatments, suggesting that S. pseudocostatum is adapted to tolerate changes of ~0.5 units of pH under high p CO 2 conditions. However, dissolved organic carbon (DOC) concentration and DOC/POC ratio were significantly higher at high p CO 2 , indicating that a greater partitioning of organic carbon into the DOC pool was stimulated by high CO 2 /low pH conditions. Total fatty acids (FAs) were significantly higher under low p CO 2 conditions. The composition of FAs changed from low to high p CO 2 , with an increase in the concentration of saturated and a reduction of monounsaturated FAs. Polyunsaturated FAs did not show significant differences between pCO 2 treatments. Our results lead to the conclusion that the balance between negative or null effect on S. pseudocostatum ecophysiology upon low pH/high pCO 2 conditions constitute an important factor to be considered in order to evaluate the global effect of rising atmospheric CO 2 on primary productivity in coastal ocean. We found a significant decrease in total FAs, however no indications were found for a detrimental effect of ocean acidification on the nutritional quality in terms of essential fatty acids.