How does this tie into GW? Maybe I'm glad you asked. Less plankton growing at the sea/ice margins. Therefore less krill; everything eats krill. Salps replacing krill; nothing eats salps.
Nature 432, 100-103 (4 November 2004) | doi: 10.1038/nature02996
Long-term decline in krill stock and increase in salps within the Southern Ocean
Angus Atkinson1, Volker Siegel2, Evgeny Pakhomov3,4 and Peter Rothery5
Top of pageAntarctic 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.
Top of pageBritish Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, UK
Sea Fisheries Institute, Palmaille 9, 22767 Hamburg, Germany
Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Rd, Vancouver, British Columbia, V6T 1Z4, Canada
Department of Zoology, Faculty of Science and Technology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa
NERC Centre for Ecology and Hydrology, CEH Monks Wood, Abbots Ripton, Huntingdon PE28 2LS, UK
Correspondence to: Angus Atkinson1 Email: aat@ bas.ac.uk
Received 17 May 2004; Accepted 7 September 2004
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