The synergy of ocean acidification and ocean warming may lead to negative marine organism responses not apparent under single stressors. While adult fish are effective acid-base regulators, and presumably less affected by environmental stressors, early life stages may be more susceptible. Pacific herring are ecologically and economically important forage fish, native to the U.S. Pacific Northwest (PNW). However, the herring populations in the PNW have experienced reductions in stock abundance. This study focused on the combined effects of ocean acidification and ocean warming on Pacific herring embryo and larval life stages. Pacific herring embryos were incubated under a factorial design of two temperature (10°C, 16°C) and two pCO2 (600 µatm, 1600 µatm) treatments until hatch. The combination of high pCO2 and high temperature revealed greater embryo respiration aberrations. Embryos reared under the high temperature treatment, for both pCO2 levels, experienced greater occurrences of larval mortality and abnormalities. These data indicate that while temperature may be a primary global change stressor affecting Pacific herring embryology and future herring populations, interactive effects with pCO2 may introduce additional challenges
