These data were collected at Shannon Point Marine Center in Washington, U.S.A. in March and May, 2021. Embryos were reared at either 10°C (ambient) or 16°C (heightened) and at either ~500 pCO2 uatm (ambient) or ~2000 pCO2 uatm (heightened). These data measure the response of winter-spawned Pacific herring embryos to critical thermal maximum excursions (CTmax) up to either 20°C or 25°C for 1, 2, or 3 hours of exposure. Percent survival was evaluated between rearing temperature and pCO2 level, maximum CTmax temperature, and duration of exposure to CTmax. The results evaluate if rearing conditions affect survival during a marine heatwave and the CTmax temperature and duration at which survival diminishes. Heart contractions assessed cardiac stress in embryos post-CTmax trials. Daily and cumulative hatching response of embryos in both March and May were measured. Hatching success (%), malformation rates in embryos (%) and malformation rates in hatched larvae (%) were measured. Oxygen consumption rates (MO2) response of winter-spawned Pacific herring embryos to variations in rearing temperature and pCO2 levels were measured.

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 2024-03-11.