The Effects of Ocean Acidification and Temperature Rise on the Thermal Tolerance and Critical Thermal Limit of Pacific…

The Effects of Ocean Acidification and Temperature Rise on the Thermal Tolerance and Critical Thermal Limit of Anthropogenic climate change is projected to affect marine ecosystems by challenging the environmental tolerance limits of individual species. The interactive effects of ocean acidification and temperature rise has been documented in a handful of marine fishes, with major physiological impacts experienced in early-life stages. Pacific herring are an important forage and commercial fish species widely distributed in coastal systems across the North Pacific. Recent studies have found temperature to be the primary stressor affecting the embryonic development of Pacific herring, but deleterious effects of ocean acidification emerged when combined with warming. In this study, Pacific herring were reared at two pCO2 levels (500 µatm or 2000 µatm) and 2-4 temperature levels (experiment 1: 10 degreesC, 12 degreesC, 14 degreesC, or 16 degreesC; experiment 2: 10 degreesC, 16 degreesC). Subsequently, A subset of embryos from the 10 degreesC and 16 degreesC treatments were exposed to critical thermal maximum (CTmax) trials that simulated the acute temperature fluctuations associated with heatwave events in shallow nearby habitats. Hatching success was primarily influenced by temperature, with a reduction from 71% (10 degreesC) to 49% (16 degreesC) in experiment 2. Preliminary CTmax results indicate that embryos were able to withstand acute exposure to 20 degreesC, but survival was greatly reduced after 2-3 hours at 25 degreesC. Parallel measurements of oxygen consumption and heart contractions revealed increased respiratory stress from CTmax exposures. Overall, this study reinforces that Pacific herring are resilient to moderate CO2 and temperature stress but are vulnerable to acute temperature increases that may accompany marine heatwave events.