- H. Flores (2)
- Hauke Flores (1)
- J.A. Franeker van (2)
- Martin Graeve (1)
- B.P.V. Hunt (1)
- Doreen Kohlbach (1)
- Thomas Krumpen (1)
- Fokje L. Schaafsma (1)
- B.A. Lange (1)
- Benjamin Lange (1)
- E.A. Pakhomov (1)
- F.L. Schaafsma (2)
- Martina Vortkamp (1)
Ice Algae-Produced Carbon Is Critical for Overwintering of Antarctic Krill Euphausia superba
Kohlbach, Doreen ; Lange, Benjamin A. ; Schaafsma, Fokje L. ; David, Carmen ; Vortkamp, Martina ; Graeve, Martin ; Franeker, Jan A. Van; Krumpen, Thomas ; Flores, Hauke - \ 2017
Frontiers in Marine Science 4 (2017). - ISSN 2296-7745 - 17 p.
Antarctic krill - euphausia-superba - fisheries resoucres - carbon source - ice algae - Marker fatty acids - Compound-specific stable isotope analysis - winter survival
Antarctic krill Euphausia superba (“krill”) constitute a fundamental food source for Antarctic seabirds and mammals, and a globally important fisheries resource. The future resilience of krill to climate change depends critically on the winter survival of young krill. To survive periods of extremely low production by pelagic algae during winter, krill are assumed to rely partly on carbon produced by ice algae. The true dependency on ice algae-produced carbon, however, is so far unquantified. This confounds predictions on the future resilience of krill stocks to sea ice decline. Fatty acid (FA) analysis, bulk stable isotope analysis (BSIA), and compound-specific stable isotope analysis (CSIA) of diatom- and dinoflagellate-associated marker FAs were applied to quantify the dependency of overwintering larval, juvenile, and adult krill on ice algae-produced carbon (aIce) during winter 2013 in the Weddell-Scotia Confluence Zone. Our results demonstrate that the majority of the carbon uptake of the overwintering larval and juvenile krill originated from ice algae (up to 88% of the carbon budget), and that the dependency on ice algal carbon decreased with ontogeny, reaching <56%of the carbon budget in adults. Spatio-temporal variability in the utilization of ice algal carbon was more pronounced in larvae and juvenile krill than in adults. Differences between aIce estimates derived from short- vs. long-term FA-specific isotopic compositions suggested that ice algae-produced carbon gained importance as the winter progressed, and might become critical at the late winter-spring transition, before the phytoplankton bloom commences. Where the sea ice season shortens, reduced availability of ice algae might possibly not be compensated by surplus phytoplankton production during wintertime. Hence, sea ice decline could seriously endanger the winter survival of recruits, and subsequently overall biomass of krill.
Community structure of under-ice fauna in relation to winter sea-ice habitat properties from the Weddell Sea
David, Carmen ; Schaafsma, F.L. ; Franeker, J.A. van; Lange, Benjamin ; Brandt, A. ; Flores, H. - \ 2017
Polar Biology 40 (2017)2. - ISSN 0722-4060 - p. 247 - 261.
Southern Ocean - Sea ice - Antarctic krill - euphausia-superba - Stephos longipes - Ctenocalanus - Zooplankton - Biomass - Diversity
Climate change-related alterations of Antarctic sea-ice habitats will significantly impact the interaction of ice-associated organisms with the environment, with repercussions on ecosystem functioning. The nature of this interaction is poorly understood, particularly during the critical period of winter–spring transition. To investigate the role of sea-ice and underlying water-column properties in structuring under-ice communities during late winter/early spring, we used a Surface and Under Ice Trawl to sample animals and environmental properties in the upper 2-m layer under the sea ice in the northern Weddell Sea from August to October 2013. The area of investigation was largely homogeneous in terms of hydrography and sea-ice coverage. We hypothesised that this apparent homogeneity in the physical regime was mirrored in the structure of the under-ice community. The under-ice community was numerically dominated by the copepods Stephos longipes, Ctenocalanus spp. and Calanus propinquus (altogether 67 %), and furcilia larvae of Antarctic krill Euphausia superba (30 %). In spite of the apparent homogeneity of the environment, abundance and biomass distributions at our sampling stations indicated the presence of three community types, following a geographical gradient in the investigation area: (1) high biomass, krill-dominated in the west, (2) high abundance, copepod-dominated in the east, and (3) low abundance, low biomass at the ice edge. Combined analysis with environmental data indicated that under-ice community structure was correlated with sea-ice coverage, chlorophyll a concentration, and bottom depth. The heterogeneity of the Antarctic under-ice community was probably also driven by other factors, such as advection, sea-ice drift, and seasonal progression. The response of under-ice communities to changing sea-ice habitats may thus considerably vary seasonally and regionally
Size and stage composition of age class 0 Antarctic krill (Euphausia superba) in the ice–water interface layer during winter/early spring
Schaafsma, F.L. ; David, C. ; Pakhomov, E.A. ; Hunt, B.P.V. ; Lange, B.A. ; Flores, H. ; Franeker, J.A. van - \ 2016
Polar Biology 39 (2016)9. - ISSN 0722-4060 - p. 1515 - 1526.
Antarctic krill - Furcilia - Juveniles - Size distribution - Under-ice habitat - Vertical distribution
The condition and survival of Antarctic krill (Euphausia superba) strongly depends on sea ice conditions during winter. How krill utilize sea ice depends on several factors such as region and developmental stage. A comprehensive understanding of sea ice habitat use by krill, however, remains largely unknown. The aim of this study was to improve the understanding of the krill’s interaction with the sea ice habitat during winter/early spring by conducting large-scale sampling of the ice–water interface (0–2 m) and comparing the size and developmental stage composition of krill with the pelagic population (0–500 m). Results show that the population in the northern Weddell Sea consisted mainly of krill that were