We studied swimming activity in the calanoid copepod Pseudocalanus acuspes in response to near- future ocean acidification. Water and copepods were sampled from ten mesocosms deployed on the Swedish west coast. The experiments were conducted on animals reared in the mesocosms for 2 months during spring. Copepods were filmed after long-term (chronic) high-CO2, and after 20 h acute exposure to CO2.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 downloaded from the PANGAEA dataset (see Source). 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 2024-11-14.

The copepods were filmed for 10 minutes with a Viewpoint Zebralab behaviour analysis system with a dragonfly firewire camera. A number of activities (unitless) were automatically quantified in real-time by the Zebralab software: total activity, number of stops, freeze duration, medium speed count, medium speed duration, burst speed counts, and burst speed duration. The behaviours were averaged for every minute of the experiment. The total swimming activity is the total change of pixels over time.