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The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill


A dominant Antarctic ecological paradigm suggests that winter sea ice is generally the main feeding ground for krill larvae. Observations from our winter cruise to the southwest Atlantic sector of the Southern Ocean contradict this view and present the first evidence that the pack-ice zone is a food-poor habitat for larval development. In contrast, the more open marginal ice zone provides a more favourable food environment for high larval krill growth rates. We found that complex under-ice habitats are, however, vital for larval krill when water column productivity is limited by light, by providing structures that offer protection from predators and to collect organic material released from the ice. The larvae feed on this sparse ice-associated food during the day. After sunset, they migrate into the water below the ice (upper 20 m) and drift away from the ice areas where they have previously fed. Model analyses indicate that this behaviour increases both food uptake in a patchy food environment and the likelihood of overwinter transport to areas where feeding conditions are more favourable in spring.

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Fig. 1: Cruise track with larval krill sampling stations.
Fig. 2: Large-scale sea-ice thickness and degree of ice formation.
Fig. 3: Larval krill on a horizontal ice floe.
Fig. 4: Larval krill growth in relation to food supply in the water column and in sea ice, and diel vertical migration behaviour.
Fig. 5: Modelled distribution of Antarctic krill larvae and mean chl a concentration for two regions of the Scotia Sea.
Fig. 6: Winter krill habitat projections in the southwest Atlantic sector of the Southern Ocean.


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We thank the captain and crew of RV Polarstern expedition WISKY (ANTXXIX-7) as well as our helicopter teams for their excellent support with work at sea, R. Schlicht for statistical consultation and B. Raymond for technical contribution to present results. This work was funded by the PACES (Polar Regions and Coasts in a changing Earth System) programme (Topic 1, WP 5) of the Helmholtz Association. Additional funds were made available via the Helmholtz Virtual Institute ‘PolarTime’ (VH-VI-500: Biological timing in a changing marine environment—clocks and rhythms in polar pelagic organisms) and the Australian Government through Antarctic Science grant #4073 and the Antarctic Climate and Ecosystem Cooperative Research Centre. S.E.T. and E.J.M. were funded by the Natural Environment Research Council under British Antarctic Survey National Capability-Ecosystems. The surface velocity data were produced by Ssalto/Duacs and distributed by Aviso, with support from Cnes ( TerraSAR-X images used to identify sampling sites were provided by German Space Agency (DLR) via the proposal “Investigation of the role of sea ice and snow properties on Antarctic krill distribution and condition in winter/spring”. We thank T. Busche (DLR) and E. Schwarz (DLR) for organizing near-real time image delivery on board of Polarstern.

Author information




B.M. and U.F. designed the research and B.M. wrote the paper with support from the co-authors. U.F., S.K. and A.G. designed the scientific dive operations with support from I.N.Y., G.N., M.T. and L.A. Ice physical investigations were performed by T.K., R.R., K.M.M. and S.S. The foraging model was designed by J.G. with support from V.G. S.E.T. and E.J.M. worked on the advection model, whereas J.M.-T., R.T., M.S., S.K. and K.M.M. performed the sea-ice model. Larval krill morphology, physiology and abundance data were collected and processed by R.K., L.H., E.P., B.P.V.H., M.T., S.J. and B.M. Sea-ice biology data were collected and analysed by L.H., B.M. and K.M.M. The climatology and water column data were collected and processed by C.K. and D.W.-G.

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Correspondence to Bettina Meyer.

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Supplementary Information

Supplementary Figures 1–11, Supplementary Tables 1–2, Supplementary Methods.

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Supplementary Video 1

Patchiness and behaviour of larvae under sea ice during the day in the pack-ice zone.

Supplementary Video 2

Patchiness and behaviour of larvae in the marginal ice zone during sunset, larvae starting to leave the ice to be dispersed in the water column.

Supplementary Video 3

Larval krill feeding on a horizontal ice floe (“terrace”).

Supplementary Video 4

Larval krill feeding on the under-side of sea ice, frozen overnight at the diving hole.

Supplementary Video 5

Larval krill dispersed in the water column during night in the pack-ice zone.

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Meyer, B., Freier, U., Grimm, V. et al. The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill. Nat Ecol Evol 1, 1853–1861 (2017).

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