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Marine Ecology Progress Series

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MEPS 362:1-23 (2008)  -  DOI:

Oceanic circumpolar habitats of Antarctic krill

A. Atkinson1,*, V. Siegel2, E. A. Pakhomov3,4, P. Rothery5, V. Loeb6, R. M. Ross7, L. B. Quetin7, K. Schmidt1, P. Fretwell1, E. J. Murphy1, G. A. Tarling1, A. H. Fleming1

1British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
2Sea Fisheries Institute, Palmaille 9, 22767 Hamburg, Germany
3Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada
4Department of Zoology, Faculty of Science and Technology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa
5Centre for Ecology and Hydrology, CEH Monks Wood, Abbots Ripton, Huntingdon PE28 2LS, UK
6Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, California 95039, USA
7Marine Science Institute, University of California at Santa Barbara, Santa Barbara, California 93106-6150, USA

ABSTRACT: Surveys of Euphausia superba often target localised shelves and ice edges where their growth rates and predation losses are atypically high. Emphasis on these areas has led to the current view that krill require high food concentrations, with a distribution often linked to shelves. For a wider, circumpolar perspective, we compiled all available net-based density data on postlarvae from 8137 mainly summer stations from 1926 to 2004. Unlike Antarctic zooplankton, the distribution of E. superba is highly uneven, with 70% of the total stock concentrated between longitudes 0° and 90°W. Within this Atlantic sector, krill are abundant over both continental shelf and ocean. At the Antarctic Peninsula they are found mainly over the inner shelf, whereas in the Indian–Pacific sectors krill prevail in the ocean within 200 to 300 km of the shelf break. Overall, 87% of the total stock lives over deep oceanic water (>2000 m), and krill occupy regions with moderate food concentrations (0.5 to 1.0 mg chl a m–3). Advection models suggest some northwards loss from these regions and into the low chlorophyll belts of the Antarctic Circumpolar Current (ACC). We found possible evidence for a compensating southwards migration, with an increasing proportion of krill found south of the ACC as the season progresses. The retention of krill in moderately productive oceanic habitats is a key factor in their high total production. While growth rates are lower than over shelves, the ocean provides a refuge from shelf-based predators. The unusual circumpolar distribution of krill thus reflects a balance between advection, migration, top–down and bottom–up processes.

KEY WORDS: Euphausiid · Circumpolar · Distribution · Growth · Mortality · Predation · Risk · Bottom–up control · Top–down control

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Cite this article as: Atkinson A, Siegel V, Pakhomov EA, Rothery P and others (2008) Oceanic circumpolar habitats of Antarctic krill. Mar Ecol Prog Ser 362:1-23.

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