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Krill (Euphausia superba) distribution contracts southward during rapid regional warming

Abstract

High-latitude ecosystems are among the fastest warming on the planet1. Polar species may be sensitive to warming and ice loss, but data are scarce and evidence is conflicting2,3,4. Here, we show that, within their main population centre in the southwest Atlantic sector, the distribution of Euphausia superba (hereafter, ‘krill’) has contracted southward over the past 90 years. Near their northern limit, numerical densities have declined sharply and the population has become more concentrated towards the Antarctic shelves. A concomitant increase in mean body length reflects reduced recruitment of juvenile krill. We found evidence for environmental controls on recruitment, including a reduced density of juveniles following positive anomalies of the Southern Annular Mode. Such anomalies are associated with warm, windy and cloudy weather and reduced sea ice, all of which may hinder egg production and the survival of larval krill5. However, the total post-larval density has declined less steeply than the density of recruits, suggesting that survival rates of older krill have increased. The changing distribution is already perturbing the krill-centred food web6 and may affect biogeochemical cycling7,8. Rapid climate change, with associated nonlinear adjustments in the roles of keystone species, poses challenges for the management of valuable polar ecosystems3.

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Fig. 1: Southward contraction of krill distribution within the Southwest Atlantic sector.
Fig. 2: A latitudinal gradation of change in krill dynamics over the past 40 years.
Fig. 3: Climatic forcing provides one mechanism for an increase in mean krill length and declines in recruitment and density.

Data availability

We have made the KRILLBASE-abundance database publically available from the Polar Data Centre at the British Antarctic Survey (http://doi.org/brg8), with supporting metadata31, which should be consulted for further details. Likewise, KRILLBASE-length frequency data are also available on request to the Polar Data Centre, with supporting metadata.

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Acknowledgements

We thank all those who have supplied their data to KRILLBASE, especially A. Baker for help with locating logbooks from the 1920s and 1930s, and R. Hewitt, R. Ross, L. Quetin and S Kawaguchi for provision of data or scientific advice. M. Jessopp, H. Peat and N. Ensor helped with compiling and checking the databases, G. Marshall advised on the SAM indices, F. Perry helped with mapping, D. Ashby helped with the infographic figure, and comments from G. Watters improved the manuscript. S.L.H. was supported by NERC core funding to the BAS Ecosystems programme. A.A. and S.F.S. were funded through NERC’s National Capability modelling, the long-term single-centre science programme ‘Climate Linked Atlantic Sector Science’ (grant number NE/R015953/1), Theme 1.3—Biological Dynamics, and the NERC and Department for Environment, Food and Rural Affairs Marine Ecosystems Research Program (NERC project numbers NE/L003066/1 and NE/L003279/1). D.K.S. was supported by the US National Science Foundation’s Antarctic Organisms and Ecosystems Program (grant PLR 1440435).

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Contributions

A.A. and S.L.H. provided the initial concept and analysis. A.A., V.S. and E.A.P. conceived and constructed the KRILLBASE databases. A.A., E.A.P., V.S., C.S.R., V.J.L., D.K.S. and G.A.T. supplied data to KRILLBASE. L.G. performed the mapping. S.L.H. performed the statistical analyses. All authors provided input of ideas to the study and manuscript.

Corresponding authors

Correspondence to Angus Atkinson or Simeon L. Hill.

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Supplementary Figures 1–5, Supplementary Table 1

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Atkinson, A., Hill, S.L., Pakhomov, E.A. et al. Krill (Euphausia superba) distribution contracts southward during rapid regional warming. Nature Clim Change 9, 142–147 (2019). https://doi.org/10.1038/s41558-018-0370-z

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