Attributing hypoxia responses of early life Menidia menidia to energetic mechanisms with Dynamic Energy Budget theory

Ocean deoxygenation is intensifying worldwide due to warming and eutrophication, particularly in estuaries and coastal waters. Although the Atlantic silverside (Menidia menidia) is tolerant of the fluctuating environmental conditions in its estuarine habitat, chronic hypoxia impairs hatching, growth, and survival in the early life stages. We used a simplified version of a Dynamic Energy Budget model (DEBkiss) to test the hypothesis that experimentally observed changes in animal performance can be explained by one or more of the rate processes in the model. We sought to identify the DEBkiss parameters that, when adjusted with a correction factor based on inhibition of Synthesizing Units, provided the best fit to hypoxia effects in the three state variables of total length, egg buffer mass, and survival over time. Because hypoxia reduces survival in embryos and newly hatched larvae, we added a survival state variable controlled by pre- and post-hatching mortality parameters. Applying the hypoxia effects to reduce the conversion efficiency of assimilates to structure accounted for some of the hypoxia-related changes in all three state variables. However, the best fit was achieved by simultaneously reducing the conversion efficiency and increasing both mortality parameters. In contrast, changing the parameter for maintenance rate with hypoxia provided little to no improvement of fit to the data. Reduced conversion efficiency under hypoxia would suggest that less of the energy invested by parents and consumed through predation is converted into biomass in M. menidia offspring, with implications for size at age that could threaten recruitment and alter the flow of energy through the food web.