title: The association of Antarctic krill Euphausia superba with the under-ice habitat.
abstract: The association of Antarctic krill Euphausia superba with the under-ice habitat was investigated in the Lazarev Sea (Southern Ocean) during austral summer, autumn and winter. Data were obtained using novel Surface and Under Ice Trawls (SUIT), which sampled the 0-2 m surface layer both under sea ice and in open water. Average surface layer densities ranged between 0.8 individuals m(-2) in summer and autumn, and 2.7 individuals m(-2) in winter. In summer, under-ice densities of Antarctic krill were significantly higher than in open waters. In autumn, the opposite pattern was observed. Under winter sea ice, densities were often low, but repeatedly far exceeded summer and autumn maxima. Statistical models showed that during summer high densities of Antarctic krill in the 0-2 m layer were associated with high ice coverage and shallow mixed layer depths, among other factors. In autumn and winter, density was related to hydrographical parameters. Average under-ice densities from the 0-2 m layer were higher than corresponding values from the 0-200 m layer collected with Rectangular Midwater Trawls (RMT) in summer. In winter, under-ice densities far surpassed maximum 0-200 m densities on several occasions. This indicates that the importance of the ice-water interface layer may be under-estimated by the pelagic nets and sonars commonly used to estimate the population size of Antarctic krill for management purposes, due to their limited ability to sample this habitat. Our results provide evidence for an almost year-round association of Antarctic krill with the under-ice habitat, hundreds of kilometres into the ice-covered area of the Lazarev Sea. Local concentrations of postlarval Antarctic krill under winter sea ice suggest that sea ice biota are important for their winter survival. These findings emphasise the susceptibility of an ecological key species to changing sea ice habitats, suggesting potential ramifications on Antarctic ecosystems induced by climate change.
authors.affiliation: Institute for Marine Resources and Ecosystem Studies, Texel, The Netherlands. hauke.flores@awi.de
authors.forename: Hauke
authors.initials: H
authors.lastname: Flores
authors.forename: Jan Andries
authors.initials: JA
authors.lastname: van Franeker
authors.forename: Volker
authors.initials: V
authors.lastname: Siegel
authors.forename: Matilda
authors.initials: M
authors.lastname: Haraldsson
authors.forename: Volker
authors.initials: V
authors.lastname: Strass
authors.forename: Erik Hubert
authors.initials: EH
authors.lastname: Meesters
authors.forename: Ulrich
authors.initials: U
authors.lastname: Bathmann
authors.forename: Willem Jan
authors.initials: WJ
authors.lastname: Wolff
mesh_terms: D000818:Animals; D000864:Antarctic Regions; D002980:Climate; D057231:Climate Change; D004463:Ecology; D017753:Ecosystem; D004777:Environment; D033201:Euphausiacea / Q000502:physiology*; D007053:Ice; D046448:Ice Cover; D016011:Normal Distribution; D009792:Oceans and Seas; D011156:Population Density; D011157:Population Dynamics; D012621:Seasons; D013696:Temperature
chemical_list: D007053:Ice