Award: OCE-1536336

The purpose of this project was to comprehensively evaluate the responses and adaptation mechanisms of an estuarine dependent fish to the combined stressors of low pH and low dissolved oxygen, stressors found commonly in coastal and estuarine waters. We focused on the early life stages as this model species as they have been shown to be sensitive to these stressors at this stage and because the effects could have population-level consequences. We hypothesized that this species would be sensitive to these stressors both individually and combined if exposed at fertilization, but that they would develop the capacity to cope with acidification very quickly after hatch. We found that growth and survival were lower in hypoxic and acidified conditions and hypothesized that energetic costs were incurred to deal with these conditions. Specifically, we predicted that oxygen consumption would increase in hypoxic and acidified conditions. In both embryos and larvae, metabolism was extremely sensitive to temperature, as was expected, but metabolic rates did not increase under high CO2 conditions alone. However, in embryos when pCO2 levels are high routine metabolism becomes depressed under hypoxia. Thus, fish become more sensitive to dissolved oxygen at high CO2 levels, explaining the strong and sometimes synergistic effect of hypoxia and acidification on fish growth and survival documented in many studies. We further quantified the production of ionocytes and gene expression of enzymes that help regulate acid-base balance in embryos and larvae as the fish developed. Again, temperature was the main determinant of ionocyte production and gene expression, but these results were dependent on the developmental stage of the fish. Overall, this estuarine fish, which serves as a model species for other estuarine dependent species, appears relatively insensitive to changes in pCO2 because of an acid-base regulation system that develops within a few days after hatch. Last Modified: 05/03/2021 Submitted by: Janet Nye