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The association of Antarctic krill Euphausia superba with the under-ice habitat.

Flores H, van Franeker JA, Siegel V, Haraldsson M, Strass V, Meesters EH, Bathmann U, Wolff WJ - PLoS ONE (2012)

Bottom Line: In summer, under-ice densities of Antarctic krill were significantly higher than in open waters.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.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.

View Article: PubMed Central - PubMed

Affiliation: Institute for Marine Resources and Ecosystem Studies, Texel, The Netherlands. hauke.flores@awi.de

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.

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Under-ice versus open water comparison of geometric mean densities of postlarval Euphausia superba in (A–B) summer (2007/2008), (C–D) autumn (2004), and (E–F) winter (2006).(A, C, E) Euphausia superba from the 0–2 m layer, and (B, D, F) from the 0–200 m layer. Error bars denote value ranges. Bold red bars indicate 25% to 75% percentile ranges. ice = under-ice, ow = open water SUIT hauls.
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pone-0031775-g004: Under-ice versus open water comparison of geometric mean densities of postlarval Euphausia superba in (A–B) summer (2007/2008), (C–D) autumn (2004), and (E–F) winter (2006).(A, C, E) Euphausia superba from the 0–2 m layer, and (B, D, F) from the 0–200 m layer. Error bars denote value ranges. Bold red bars indicate 25% to 75% percentile ranges. ice = under-ice, ow = open water SUIT hauls.

Mentions: The density of postlarval Antarctic krill in the 0–200 m stratum significantly differed among the sampling seasons (ANOVA: p<0.01), but was not significantly related to the presence of sea ice (ANOVA: p>0.1). In summer, both the average and geometric mean densities in the 0–200 m stratum were lower than in the 0–2 m layer in ice-covered waters, but above the values of the 0–2 m surface layer in open waters (Figure 4 A, B). In autumn, however, average and geometric mean densities were considerably higher in the 0–200 m depth layer than in the 0–2 m surface layer, both in open water and under ice (Figure 4 C, D). In winter, average krill density in the 0–200 m stratum was below the average density from the ice-water interface layer, mainly due to a few exceptionally high SUIT catches yielding densities up to 5 times above maximum values from the 0–200 m layer (Figure 1 C). Because of this high variability in the SUIT data, geometric mean densities showed the opposite pattern (Figure 4 E, F).


The association of Antarctic krill Euphausia superba with the under-ice habitat.

Flores H, van Franeker JA, Siegel V, Haraldsson M, Strass V, Meesters EH, Bathmann U, Wolff WJ - PLoS ONE (2012)

Under-ice versus open water comparison of geometric mean densities of postlarval Euphausia superba in (A–B) summer (2007/2008), (C–D) autumn (2004), and (E–F) winter (2006).(A, C, E) Euphausia superba from the 0–2 m layer, and (B, D, F) from the 0–200 m layer. Error bars denote value ranges. Bold red bars indicate 25% to 75% percentile ranges. ice = under-ice, ow = open water SUIT hauls.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3285626&req=5

pone-0031775-g004: Under-ice versus open water comparison of geometric mean densities of postlarval Euphausia superba in (A–B) summer (2007/2008), (C–D) autumn (2004), and (E–F) winter (2006).(A, C, E) Euphausia superba from the 0–2 m layer, and (B, D, F) from the 0–200 m layer. Error bars denote value ranges. Bold red bars indicate 25% to 75% percentile ranges. ice = under-ice, ow = open water SUIT hauls.
Mentions: The density of postlarval Antarctic krill in the 0–200 m stratum significantly differed among the sampling seasons (ANOVA: p<0.01), but was not significantly related to the presence of sea ice (ANOVA: p>0.1). In summer, both the average and geometric mean densities in the 0–200 m stratum were lower than in the 0–2 m layer in ice-covered waters, but above the values of the 0–2 m surface layer in open waters (Figure 4 A, B). In autumn, however, average and geometric mean densities were considerably higher in the 0–200 m depth layer than in the 0–2 m surface layer, both in open water and under ice (Figure 4 C, D). In winter, average krill density in the 0–200 m stratum was below the average density from the ice-water interface layer, mainly due to a few exceptionally high SUIT catches yielding densities up to 5 times above maximum values from the 0–200 m layer (Figure 1 C). Because of this high variability in the SUIT data, geometric mean densities showed the opposite pattern (Figure 4 E, F).

Bottom Line: In summer, under-ice densities of Antarctic krill were significantly higher than in open waters.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.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.

View Article: PubMed Central - PubMed

Affiliation: Institute for Marine Resources and Ecosystem Studies, Texel, The Netherlands. hauke.flores@awi.de

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.

Show MeSH