Our study investigated the combined effects of ocean acidification and P. gemini infection on germination of eelgrass seeds. We conducted a two-level factorial experiment crossing four pH levels (Δ0, - Δ0.3, - Δ0.6, -Δ0.9; relative to the average pH at the sampling site) with three infection levels (infected, non-infected, exposed) to determine germination rate and infection response. Prior to experimentation, flowering shoots were collected and held in flow-through seawater tanks where seeds ripened naturally. Once collected, seeds were held in copper sulfate solution (27.37 ± 1.57 ppt) and stored in darkness to mimic winter dormancy (4 ◦C). Before the start of the experiment, viable seeds were cultured on oomycete selective growth media to determine infection status.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 2025-01-22.