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Risk maps for Antarctic krill under projected Southern Ocean acidification

Abstract

Marine ecosystems of the Southern Ocean are particularly vulnerable to ocean acidification1. Antarctic krill (Euphausia superba; hereafter krill) is the key pelagic species of the region and its largest fishery resource2. There is therefore concern about the combined effects of climate change, ocean acidification and an expanding fishery on krill and ultimately, their dependent predators—whales, seals and penguins3,4. However, little is known about the sensitivity of krill to ocean acidification. Juvenile and adult krill are already exposed to variable seawater carbonate chemistry because they occupy a range of habitats and migrate both vertically and horizontally on a daily and seasonal basis5. Moreover, krill eggs sink from the surface to hatch at 700–1,000 m (ref. 6), where the carbon dioxide partial pressure ( p CO 2 ) in sea water is already greater than it is in the atmosphere7. Krill eggs sink passively and so cannot avoid these conditions. Here we describe the sensitivity of krill egg hatch rates to increased CO2, and present a circumpolar risk map of krill hatching success under projected p CO 2 levels. We find that important krill habitats of the Weddell Sea and the Haakon VII Sea to the east are likely to become high-risk areas for krill recruitment within a century. Furthermore, unless CO2 emissions are mitigated, the Southern Ocean krill population could collapse by 2300 with dire consequences for the entire ecosystem.

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Figure 1: Observed (open symbols) and modelled mean (black squares) krill egg hatch rates at six experimental p CO 2 levels.
Figure 2: Egg hatching success under different CO2 treatments.
Figure 3: Future projection of p CO 2 in the Southern Ocean.
Figure 4: Circumpolar risk maps of krill hatching success under projected future p CO 2 levels.

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Acknowledgements

The authors thank S. Wotherspoon for advice on statistical analyses, B. Smith and Z. Jia for assisting with the experiments, J. Robinson for assistance in assembling the experimental system, and C. Wynn-Edwards for assisting with krill maintenance. The model projections were performed on the super computer at JAMSTEC. This study was supported by Australian Antarctic Science Program Project No. 4037.

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This study was initiated, designed, coordinated and analysed by S.K. Ocean carbon model projection was undertaken by A. Ishida. Experimental system was designed and assembled by R.K. Statistical modelling and analyses were undertaken by B.R. Experiments were undertaken by N.W. All authors made intellectual contribution. The manuscript was written by S.K. and edited by A. Ishida, R.K., B.R., A.C., S.N., M.W. and A. Ishimatsu.

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Correspondence to S. Kawaguchi.

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The authors declare no competing financial interests.

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Kawaguchi, S., Ishida, A., King, R. et al. Risk maps for Antarctic krill under projected Southern Ocean acidification. Nature Clim Change 3, 843–847 (2013). https://doi.org/10.1038/nclimate1937

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  • DOI: https://doi.org/10.1038/nclimate1937

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