Interactive effects of ocean acidification and ocean warming on Pacific herring (Clupea pallasi) early life stages

The synergy of ocean acidification and ocean warming may lead to negative effects in marine organism responses that would be absent under single stressors. While adult fish are effective acid-base regulators, early life stages may be more susceptible to environmental stressors. Pacific herring are ecologically and economically important forage fish native to the U.S. Pacific Northwest (PNW), and several herring populations in the PNW have experienced reductions in stock abundance. Studies to date have focused on Atlantic herring, and little is known about the response of Pacific herring to ocean acidification and warming. Therefore, this study focused on the combined effects of ocean acidification and warming on Pacific herring early life stages. We incubated Pacific herring embryos under a factorial design of two temperature (10 degreesC, 16 degreesC) and two pCO2 (600 µatm, 1200 µatm) treatments from fertilization until hatch (11 to 15 days depending on temperature). Elevated pCO2 was associated with a small increase in embryo mortality. However, elevated temperature was associated with greater embryo mortality, greater embryo heart rates and yolk areas upon hatch, lower percent normal hatch, and decreased larval lengths. The interaction of elevated temperature and pCO2 was associated greater embryo respiration rates and yolk areas. This study indicates that temperature will likely be the primary global change stressor affecting Pacific herring embryology, and interactive effects with pCO2 may introduce additional challenges.