Ocean acidification alters fish populations indirectly through habitat modification


Ocean ecosystems are predicted to lose biodiversity and productivity from increasing ocean acidification1. Although laboratory experiments reveal negative effects of acidification on the behaviour and performance of species2,3, more comprehensive predictions have been hampered by a lack of in situ studies that incorporate the complexity of interactions between species and their environment. We studied CO2 vents from both Northern and Southern hemispheres, using such natural laboratories4 to investigate the effect of ocean acidification on plant–animal associations embedded within all their natural complexity. Although we substantiate simple direct effects of reduced predator-avoidance behaviour by fishes, as observed in laboratory experiments, we here show that this negative effect is naturally dampened when fish reside in shelter-rich habitats. Importantly, elevated CO2 drove strong increases in the abundance of some fish species through major habitat shifts, associated increases in resources such as habitat and prey availability, and reduced predator abundances. The indirect effects of acidification via resource and predator alterations may have far-reaching consequences for population abundances, and its study provides a framework for a more comprehensive understanding of increasing CO2 emissions as a driver of ecological change.

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Figure 1: In situ escape responses (mean ± s.e.m.) by fish from an approaching threat at White Island (top panels; N = 146 fish per response) and Vulcano Island (bottom panels; N = 209 fish) CO2 vent and control sites.
Figure 2: Habitat composition and fish–habitat association at CO2 vent and control sites.
Figure 3: Population structure of fish and predators at CO2 vents and control sites.


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We thank T. Rossi for help in the field and design of Supplementary Fig. 2 and G. Grammer for assisting with fish otolith dissections. Financial support was provided by the Environment Institute (The University of Adelaide) and ARC future fellowships to I.N. (grant no. FT120100183), S.D.C. (grant no. FT0991953) and B.M.G. (grant no. FT100100767), and an ARC Discovery grant to B.D.R. and S.D.C. (DP150104263).

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I.N. and S.D.C. conceived and designed the experiments. I.N. and S.D.C. performed the experiments. I.N., B.D.R. and S.D.C. analysed the data. B.D.R. and B.M.G. contributed materials/analysis tools. All authors contributed to writing the manuscript.

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Correspondence to Ivan Nagelkerken.

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The authors declare no competing financial interests.

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Nagelkerken, I., Russell, B., Gillanders, B. et al. Ocean acidification alters fish populations indirectly through habitat modification. Nature Clim Change 6, 89–93 (2016). https://doi.org/10.1038/nclimate2757

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