This study was designed to assess the physiological cost of resilience to acidification in the hard clam (Mercenaria mercenaria, also known as northern quahog). We examined growth and susceptibility to bacterial infection of larval and juvenile clams reared in seawater with altered pCO2. We specifically focused on changes in immune performances, measured as alterations of resistance of larvae and juveniles towards opportunistic Vibrio spp., among clams exposed to acidified seawater. By examining different life history stages, we were able to document differences in exposure time to acidification as well as potential carry-over effects. To determine if increased susceptibility to infection was direct or indirect, we examined the response of the Vibrio species used in the bacterial challenge to different pH treatments and their native presence in the treatment tanks prior to bacterial challenges. Furthermore, we determined if reduced immune function induced by exposure to acidification was permanent or if clams can rebound and restore immunity after transfer to low pCO2/high pH conditions (indicating a plastic response and/or a selection event) and if early survival in OA conditions was related to success at later stages (through either acclimation or carry over effects).

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 2024-03-28.