Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Long-term decline in krill stock and increase in salps within the Southern Ocean


Antarctic krill (Euphausia superba) and salps (mainly Salpa thompsoni) are major grazers in the Southern Ocean1,2,3,4, and krill support commercial fisheries5. Their density distributions1,3,4,6 have been described in the period 1926–51, while recent localized studies7,8,9,10 suggest short-term changes. To examine spatial and temporal changes over larger scales, we have combined all available scientific net sampling data from 1926 to 2003. This database shows that the productive southwest Atlantic sector contains >50% of Southern Ocean krill stocks, but here their density has declined since the 1970s. Spatially, within their habitat, summer krill density correlates positively with chlorophyll concentrations. Temporally, within the southwest Atlantic, summer krill densities correlate positively with sea-ice extent the previous winter. Summer food and the extent of winter sea ice are thus key factors in the high krill densities observed in the southwest Atlantic Ocean. Krill need the summer phytoplankton blooms of this sector, where winters of extensive sea ice mean plentiful winter food from ice algae, promoting larval recruitment7,8,9,10,11 and replenishing the stock. Salps, by contrast, occupy the extensive lower-productivity regions of the Southern Ocean and tolerate warmer water than krill2,3,4,12. As krill densities decreased last century, salps appear to have increased in the southern part of their range. These changes have had profound effects within the Southern Ocean food web10,13.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Prices vary by article type



Prices may be subject to local taxes which are calculated during checkout

Figure 1: Krill, salps and their food.
Figure 2: Temporal change of krill and salps.
Figure 3: Krill–ice relationships.


  1. Marr, J. W. S. The natural history and geography of the Antarctic krill (Euphausia superba Dana). Discovery Rep. 32, 33–464 (1962)

    Google Scholar 

  2. Le Fèvre, J., Legendre, L. & Rivkin, R. B. Fluxes of biogenic carbon in the Southern Ocean: roles of large microphagous zooplankton. J. Mar. Syst. 17, 325–345 (1998)

    Article  ADS  Google Scholar 

  3. Pakhomov, E. A., Froneman, P. W. & Perissinotto, R. Salp/krill interactions in the Southern Ocean: spatial segregation and implications for the carbon flux. Deep-Sea Res. II 49, 1881–1907 (2002)

    Article  ADS  CAS  Google Scholar 

  4. Foxton, P. The distribution and life history of Salpa thompsoni Foxton with observations on a related species, Salpa gerlachei. Discovery Rep. 34, 1–116 (1966)

    Google Scholar 

  5. Everson, E. Krill. Biology, Ecology and Fisheries (Blackwell Science, London, 2000)

    Google Scholar 

  6. Baker, A. de C. The circumpolar continuity of Antarctic plankton species. Discovery Rep. 27, 201–218 (1954)

    Google Scholar 

  7. Siegel, V. Krill (Euphausiacea) demography and variability in abundance and distribution. Can. J. Fish. Aquat. Sci. 57, 151–167 (2000)

    Article  Google Scholar 

  8. Loeb, V. et al. Effects of sea-ice extent and krill or salp dominance on the Antarctic food web. Nature 387, 897–900 (1997)

    Article  ADS  CAS  Google Scholar 

  9. Quetin, L. B. & Ross, R. M. Episodic recruitment in Antarctic krill Euphausia superba in the Palmer LTER study region. Mar. Ecol. Prog. Ser. 259, 185–200 (2003)

    Article  ADS  Google Scholar 

  10. Fraser, W. R. & Hofmann, E. E. A predator's perspective on causal links between climate change, physical forcing and ecosystem response. Mar. Ecol. Prog. Ser. 265, 1–15 (2003)

    Article  ADS  Google Scholar 

  11. Quetin, L. B., Ross, R. M., Frazer, T. K. & Haberman, K. L. Factors affecting distribution and abundance of zooplankton, with an emphasis on Antarctic krill, Euphausia superba. Antarct. Res. Ser. 70, 357–371 (1996)

    Article  Google Scholar 

  12. Nicol, S. et al. Ocean circulation off east Antarctica affects ecosystem structure and sea-ice extent. Nature 406, 504–507 (2000)

    Article  ADS  CAS  Google Scholar 

  13. Reid, K. & Croxall, J. P. Environmental response of upper trophic-level predators reveals a system change in an Antarctic marine ecosystem. Proc. R. Soc. Lond. B 268, 377–384 (2001)

    Article  CAS  Google Scholar 

  14. Nicol, S., Constable, A. & Pauly, T. Estimates of circum-polar Antarctic krill abundance based on recent acoustic density measurements. CCAMLR Sci. 7, 87–99 (2000)

    Google Scholar 

  15. Brierley, A. S. et al. Antarctic krill under sea ice: elevated abundance in a narrow band just south of the ice edge. Science 295, 1890–1892 (2002)

    Article  ADS  CAS  Google Scholar 

  16. Tynan, C. Ecological importance of the Southern Boundary of the Antarctic Circumpolar Current. Nature 392, 708–710 (1998)

    Article  ADS  CAS  Google Scholar 

  17. Constable, A. J., Nicol, S. & Strutton, P. G. Southern Ocean productivity in relation to spatial and temporal variation in the physical environment. J. Geophys Res. 108, doi: 101029/2001JC001270 (2003)

  18. Arrigo, K. R., Worthen, D., Schnell, A. & Lizotte, M. P. Primary production in Southern Ocean waters. J. Geophys. Res. 103, 15587–15600 (1998)

    Article  ADS  Google Scholar 

  19. Hofmann, E. E., Klinck, J. M., Locarnini, R. A., Fach, B. & Murphy, E. Krill transport in the Scotia Sea and environs. Antarct. Sci. 10, 406–415 (1998)

    Article  ADS  Google Scholar 

  20. Murphy, E. J. Spatial structure of the Southern Ocean ecosystem: predator-prey linkages in Southern Ocean food webs. J. Anim. Ecol. 64, 333–347 (1995)

    Article  Google Scholar 

  21. Laws, R. M. The ecology of the Southern Ocean. Am. Sci. 73, 26–40 (1985)

    ADS  Google Scholar 

  22. Smetacek, V., Scharek, R. & Nöthig, E. M. in Antarctic Ecosystems. Ecological Change and Conservation (eds Kerry, K. R. & Hempel, G.) 103–114 (Springer, Berlin, 1990)

    Book  Google Scholar 

  23. Hofmann, E. E. & Hüsrevoğlu, Y. S. A circumpolar modelling study of habitat control of Antarctic krill (Euphausia superba) reproductive success. Deep-Sea Res. II 50, 3121–3142 (2003)

    Article  ADS  Google Scholar 

  24. Parkinson, C. L. Trends in the length of the Southern Ocean sea-ice season, 1979–99. Ann. Glaciol. 34, 435–440 (2002)

    Article  ADS  Google Scholar 

  25. Gille, S. T. Warming of the Southern Ocean since the 1950s. Science 295, 1275–1277 (2002)

    Article  ADS  CAS  Google Scholar 

  26. de la Mare, W. K. Abrupt mid-twentieth-century decline in Antarctic sea ice from whaling records. Nature 389, 57–60 (1997)

    Article  ADS  CAS  Google Scholar 

  27. Clarke, A. & Harris, C. M. Polar marine ecosystems: major threats and future change. Environ. Conserv. 30, 1–25 (2003)

    Article  Google Scholar 

  28. Curran, M. A. J., van Ommen, T. D., Morgan, V. I., Phillips, K. L. & Palmer, A. S. Ice core evidence for Antarctic sea ice decline since the 1950s. Science 302, 1203–1206 (2003)

    Article  ADS  CAS  Google Scholar 

  29. Moore, J. K., Abbott, M. R. & Richman, J. G. Location and dynamics of the Antarctic Polar front from satellite sea surface temperature data. J. Geophys. Res. 104, 3059–3073 (1999)

    Article  ADS  Google Scholar 

  30. Orsi, A. H., Whitworth, T. III & Nowlin, W. D. J. On the meridional extent and fronts of the Antarctic Circumpolar Current. Deep-Sea Res. I 42, 641–673 (1995)

    Article  Google Scholar 

Download references


We thank V. Loeb and R. Hewitt for sharing the extensive data from the AMLR Program; A. Clarke, G. Hosie, S. Chiba, J. Nishikawa, R. Anadón, P. Ward and A. de C. Baker for providing further data and information; P. Fretwell, A. Fleming, S. Grant and S. Thorpe for data handling; and A. Hirst, A. Clarke, P. Ward, K. Schmidt, D. Pond, P. Trathan, G. Tarling and E. Murphy for comments. Satellite data were provided courtesy of NASA GSFC, the SeaWiFS Project and NOAA. The Department of Environmental Affairs & Tourism (Pretoria, South Africa) provided funds and facilities for South African collections, through the South African National Antarctic Program. A.A.'s contribution was funded under the British Antarctic Survey's DYNAMOE Programme.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Angus Atkinson.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Information Main Text

Focus on the three key results of the paper, expanding on their robustness to possible artefacts of sampling. Includes Supplementary Information tables 3and 4, and Supplementary Figure captions. (DOC 52 kb)

Supplementary Table 2

Data collection information — metadata for the complete database (follows main text table 1). (XLS 63 kb)

Supplementary Figure 4

Krill distribution (follows main text Figs 1–3). (PPT 472 kb)

Supplementary Figure 5

Fine-scale sampling coverage in the South West Atlantic sector. (PPT 464 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Atkinson, A., Siegel, V., Pakhomov, E. et al. Long-term decline in krill stock and increase in salps within the Southern Ocean. Nature 432, 100–103 (2004).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing