Using a complex experimental design, we investigated what part of the pH variability is driving the biological response of the sea urchin Echinus esculentus larvae. Comparing stable (pH 8.13, 7.82, 7.53) and fluctuating treatments (12 h at pH 8.13 and 12 h at pH 7.53) following natural or inverted diurnal cycles.This dataset is included in the OA-ICC data compilation maintained in the framework of the IAEA Ocean Acidification International Coordination Centre (see https://oa-icc.ipsl.fr). Original data were extracted from tables in the related paper (see Related to) by the OA-ICC data curator. In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Gattuso et al, 2024) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI). The date of carbonate chemistry calculation by seacarb is 2024-06-12.