The effects of ocean acidification and temperature rise on the thermal tolerance and critical thermal limit of Pacific herring (Clupea pallasii)

Anthropogenic climate change, including the interactive effects of ocean acidification and temperature rise, is projected to affect marine ecosystems by challenging the environmental tolerance limits of individual species. Such impacts have been documented in a handful of marine fishes, including major physiological effects experienced in early-life stages of Pacific herring, an important forage and commercial fish species widely distributed in coastal systems across the North Pacific. In this study, we investigated the effects of temperatures between 10-16Β°C and two pCO2 levels (ambient and high pCO2) on hatching and survival of Pacific herring. Survival after acute temperature exposure was assessed and compared between incubation treatments, as may be experienced by herring egg deposits during low tide on warm days. We compared early and late spawning populations to determine if their responses differed when exposed to chronic temperature and pCO2 conditions and to short term temperature stress. A subset of embryos from the 10Β°C and 16Β°C treatments were exposed to critical thermal maximum (πΆπ‘‡π‘šπ‘Žπ‘₯) trials that simulated the acute temperature fluctuations associated with marine heat waves and tidal processes in shallow nearshore habitats. Hatching success was primarily influenced by temperature in both winter and spring embryos. πΆπ‘‡π‘šπ‘Žπ‘₯ results indicate that embryos were able to withstand acute exposure to 20Β°C regardless of spawning population or incubation treatments, but survival was greatly reduced after 2-3 hours at 25Β°C. Post-exposure heart contraction measurements revealed a greater rate of increase in heart rate in the combined treatment of 10Β°C and πΆπ‘‡π‘šπ‘Žπ‘₯ duration hours compared to 16Β°C, suggesting respiratory acclimation at higher incubation temperatures. Oxygen consumption rates (MO2) measured at stable incubation conditions resulted in higher MO2 values at elevated temperatures and pCO2 levels. Overall, this study reinforces that Pacific herring are resilient to moderate pCO2 and temperature stress but are vulnerable to acute temperature increases that may accompany marine heatwave events and late season low tide temperatures, and in some cases the combination of elevated pCO2 and temperature can introduce additional challenges for these important forage fish.

Singh N. R., 2022. The effects of ocean acidification and temperature rise on the thermal tolerance and critical thermal limit of Pacific herring (Clupea pallasii). MSc thesis, Western Washington University, 79 p. Thesis.

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