The effects of ocean acidification and reduced oxygen on the behavior and physiology of juvenile rockfish

As climate change progresses, the frequency and duration of upwelling events that bring low pH, low dissolved oxygen (DO) water to nearshore habitats are expected to increase. In addition, long-term global changes in ocean pH and DO are expected to occur within the next few decades to centuries. Locally, there have been documented reductions in near-shore pH along with the expansion of oxygen minimum zones within the California Current System. However, very few studies have investigated the potential interactive effect of these stressors on temperate reef fish. For this thesis, two sets of laboratory experiments were conducted to determine the independent and interactive effects of reduced pH and DO on the behavior and physiology of juvenile rockfish (Sebastes caurinus and Sebastes melanops). Behavioral studies examined fish boldness using an escape trial and brain lateralization by testing the consistency of individual fishes’ turning preference. Physiological studies measured critical swimming speed (Ucrit), ventilation rate, standard metabolic rate (SMR), maximum metabolic rate (MMR), critical oxygen tension (Pcrit), aerobic scope, and growth rate. Over the range of conditions examined, DO proved to have a much stronger effect on rockfish physiology than pH, suggesting that low-oxygen events may be more detrimental to individual fitness than ocean acidification. Significant effects of reduced DO on rockfish physiology include impaired swimming performance in S. caurinus and increased ventilation rate in S. melanops, but substantive responses in metabolic rates (e.g. SMR, MMR, aerobic scope, Pcrit) were not observed. Juveniles of both species appear to be behaviorally resilient to exposure to reduced pH and DO. Together, these experiments address important questions regarding how temperate reef fish will respond to both the independent and interactive effect of these oceanographic stressors. Finally, they set the framework for studying species-specific susceptibility to pH and DO stressors.

Flannery C. H., 2018. The effects of ocean acidification and reduced oxygen on the behavior and physiology of juvenile rockfish. MSc thesis, Humboldt State University, 139 p. Thesis.

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