This dataset contains physiological and carbonate chemistry data for the green macroalgae species Ulva fasciata Delile, collected from the Mediterranean coast of Mersin, Türkiye, in March 2014 and cultured under controlled laboratory conditions. The experiment was conducted using a factorial design comprising two pH levels representing ambient pH and reduced pH conditions, and two irradiance treatments: PAR and PAR + UVA + UVB. The dataset includes daily growth rate, chlorophyll a and b, photosynthetic parameters, carbonic anhydrase and nitrate reductase activities, UV-absorbing compounds, and seawater carbonate chemistry parameters calculated using CO2SYS.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 provided by the author of the related paper (see Related to) to 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 2026-05-14.