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The Combined Impact of Hypoxia and Ocean Acidification on Four Estuarine Fishes

Paper Reviewed
Dixon, R.L., Grecay, P.A. and Targett, T.E. 2017. Responses of juvenile Atlantic silverside, striped killifish, mummichog, and striped bass to acute hypoxia and acidification: Aquatic surface respiration and survival. Journal of Experimental Marine Biology and Ecology 493: 20-30.

Significant daily fluctuations in dissolved oxygen and pH occur in estuarine environments across a wide range of spatial and temporal scales in response to both biotic and abiotic processes. Understanding the extent to which different species of marine life can cope and mitigate stress in these variable environments is of significant importance, especially in light of future projections of rising atmospheric CO2 concentrations that are expected to reduce the pH of the world's oceans. The latest scientific team to investigate this topic is Dixon et al. (2017).

Using a controlled-environment system, the three researchers investigated the stress response of four estuarine fish species to the combined stress of declining dissolved oxygen (hypoxia) and seawater pH (so-called ocean acidification). The four fish species included Atlantic silversides (Menidia menidia), striped killifish (Fundulus majalis), mummichog (Fundulus heteroclitus) and juvenile striped bass (Morone saxatilis). Dissolved oxygen (DO) and pH treatments included both a moderate and an extreme range, with DO and pH fluctuations ranging between 1 and 11 mg O2 l-1 and 6.8 to 8.1, respectively, over separate 4- and 16-hour exposure periods.

Results of the experiment revealed that there was "no evidence of a pH (pCO2) effect on ASR [(an indicator of stress response)] or survival in any species in response to naturally co-varying DO and pH swings, despite pH as low as 6.8 and high pCO2 levels of ≥ ~12,000 µatm." Consequently, we can confidently conclude that the projected decline in oceanic pH resulting from humanity's combustion of hydrocarbon fuels will pose little, if any, threat to the four marine fishes examined here.

Posted 3 January 2018