Ocean acidification and hypoxia can have opposite effects on rockfish otolith growth


• Elevated CO2 and reduced dissolved oxygen have opposite effects on otolith (earstone) development in juvenile copper and blue rockfish.

• Increased CO2 levels resulted in otoliths being larger in area for a relative fish body size in blue rockfish.

• Reduced dissolved oxygen levels results in otoliths being smaller in area for a relative fish body size in both species.


Climate change is predicted to alter ocean chemistry through warming temperatures, increases in CO2 (i.e., ocean acidification), and reductions in dissolved oxygen (DO) (i.e., hypoxia). Past research has shown that early life stages of marine fishes are sensitive to all three stressors, but with sometimes different directions of response. In this study, we examined the separate effects of ocean acidification and hypoxia on otolith growth in two species of juvenile rockfish (copper rockfish, Sebastes caurinus, and blue rockfish, Sebastes mystinus). Fishes were collected at settlement stage from kelp forests on the central California coast and reared in the laboratory for up to 6 months in 4 separate pH treatments (pH = 7.3, 7.6, 7.8, and a control of 8.0), simulating the effects of ocean acidification through the addition of CO2, and 4 separate dissolved oxygen treatments (DO = 2.2, 4.1, 6.0, and a control of 8.7 mg/L), simulating the effects of hypoxia. For both species, otoliths were smaller for a given fish length in response to hypoxia but were larger (trend was non-significant for copper rockfish) in response to elevated CO2. The results suggest that otolith growth may respond differently to ocean acidification and hypoxia for some species, which has implications for sensory development, ecological performance, and interpretations of the permanent record of fish growth in hard parts such as otoliths.

Hamilton S. L., Kashef N. S., Stafford D. M., Mattiasen E. G., Kapphahn L. A., Logan C. A., Bjorkstedt E. P. & Sogard S. M., 2019. Ocean acidification and hypoxia can have opposite effects on rockfish otolith growth. Journal of Experimental Marine Biology and Ecology 521: 151245. doi: 10.1016/j.jembe.2019.151245. Article (subscription required).

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Ocean acidification in the IPCC AR5 WG II

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