Seasonal changes in the vertical distribution and community structure of Antarctic macrozooplankton and micronekton

Abstract

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. b s t r a c tThe macrozooplankton and micronekton community of the Lazarev Sea (Southern Ocean) was investigated at 3 depth layers during austral summer, autumn and winter: (1) the surface layer (0-2 m); (2) the epipelagic layer (0-200 m); and (3) the deep layer (0-3000 m). Altogether, 132 species were identified. Species composition changed with depth from a euphausiid-dominated community in the surface layer, via a siphonophore-dominated community in the epipelagic layer, to a chaetognathdominated community in the deep layer. The surface layer community predominantly changed along gradients of surface water temperature and sea ice parameters, whereas the epipelagic community mainly changed along hydrographical gradients. Although representing only 1% of the depth range of the epipelagic layer, mean per-area macrofauna densities in the surface layer ranged at 8% of corresponding epipelagic densities in summer, 6% in autumn, and 24% in winter. Seasonal shifts of these proportional densities in abundant species indicated different strategies in the use of the surface layer, including both hibernal downward and hibernal upward shift in the vertical distribution, as well as year-round surface layer use by Antarctic krill. These findings imply that the surface layer, especially when it is ice-covered, is an important functional node of the pelagic ecosystem that has been underestimated by conventional depth-integrated sampling in the past. The exposure of this key habitat to climate-driven forces most likely adds to the known susceptibility of Antarctic pelagic ecosystems to temperature rise and changing sea ice conditions.

Community structure of under-ice fauna in relation to winter sea-ice habitat properties from the Weddell Sea

“…meso-and macrofauna dwelling at the sea ice-water interface layer. Previous research has shown that the community near the sea ice-water interface differs from the community in deeper water in terms of species composition and density, and community structure (Flores et al 2011(Flores et al , 2014. Typically, the surface community is integrated into the epipelagic community (White and Piatkowski 1993;Fisher et al 2004;Hunt et al 2011;Giesecke and González 2012).…”

Size and stage composition of age class 0 Antarctic krill (Euphausia superba) in the ice–water interface layer during winter/early spring

“…It should also be kept in mind that the RMT samples in the wake of the ship and therefore in disturbed sea ice conditions. Earlier comparisons of SUIT and RMT data also indicated that the RMT does not sample the ice-water interface well (Flores et al 2011(Flores et al , 2012a(Flores et al , 2014. Abundances calculated from the SUIT catch are probably underestimations due to the low efficiency of the SUIT to sample krill from sea ice crevices and over-rafted ice floes, where larval krill have been found to reside (Frazer et al 2002;Meyer et al 2009;Flores et al 2012b).…”

“…Sub-adult and adult krill show variation in vertical migration behaviour and depth of occurrence, depending on region and season (Mauchline and Fisher 1969;Marr 1962;Pakhomov 1995;Watkins 2000;Flores et al 2012a;Siegel 2005). In a multi-seasonal study from the Lazarev Sea comparing the surface layer with deeper depth strata, the post-larval E. superba distribution patterns are variable and different from that of AC0 krill (Flores et al 2014). The trade-off of AC1 juveniles and (sub-) adults is likely different from that of larvae and AC0 juveniles due to, e.g., different (vertebrate) predators and/or food requirement (Quetin et al 1996;Siegel 2005;Flores et al 2012a).…”

“…The comparison of krill abundances should be considered with caution because the effect of, e.g., towing speed, sea ice conditions or other factors on the catch efficiency of both nets is not precisely known (Flores et al 2012a(Flores et al , 2014. Hunt et al (2014) showed that, at least in the eastern part of the sampling area, AC0 krill were migrating from the icewater interface down to \20 m at night.…”

“…The macrozooplankton/micronekton community residing within the under-ice surface layer has previously been shown to differ from the epipelagic layer in terms of species composition, community structure and species density (Flores et al 2012a(Flores et al , 2014. In this study, krill assemblages were investigated from different depth strata of the northern Weddell Sea during austral winter/early spring.…”