Ice Algae-Produced Carbon Is Critical for Overwintering of Antarctic Krill Euphausia superba

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 (αIce) 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 αIce 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

Point Mutations in GLI3 Lead to Misregulation of its Subcellular Localization

Background Mutations in the transcription factor GLI3, a downstream target of Sonic Hedgehog (SHH) signaling, are responsible for the development of malformation syndromes such as Greig-cephalopolysyndactyly-syndrome (GCPS), or Pallister-Hall-syndrome (PHS). Mutations that lead to loss of function of the protein and to haploinsufficiency cause GCPS, while truncating mutations that result in constitutive repressor function of GLI3 lead to PHS. As an exception, some point mutations in the C-terminal part of GLI3 observed in GCPS patients have so far not been linked to loss of function. We have shown recently that protein phosphatase 2A (PP2A) regulates the nuclear localization and transcriptional activity a of GLI3 function. Principal Findings We have shown recently that protein phosphatase 2A (PP2A) and the ubiquitin ligase MID1 regulate the nuclear localization and transcriptional activity of GLI3. Here we show mapping of the functional interaction between the MID1-α4-PP2A complex and GLI3 to a region between amino acid 568-1100 of GLI3. Furthermore we demonstrate that GCPS-associated point mutations, that are located in that region, lead to misregulation of the nuclear GLI3-localization and transcriptional activity. GLI3 phosphorylation itself however appears independent of its localization and remains untouched by either of the point mutations and by PP2A-activity, which suggests involvement of an as yet unknown GLI3 interaction partner, the phosphorylation status of which is regulated by PP2A activity, in the control of GLI3 subcellular localization and activity. Conclusions The present findings provide an explanation for the pathogenesis of GCPS in patients carrying C-terminal point mutations, and close the gap in our understanding of how GLI3-genotypes give rise to particular phenotypes. Furthermore, they provide a molecular explanation for the phenotypic overlap between Opitz syndrome patients with dysregulated PP2A-activity and syndromes caused by GLI3-mutations

Euphausiid catch numbers of PS 82 (ANT XXIX/9) from rectangular midwater trawl sampling

Count numbers and filtered volumes of euphausiids (Euphausia superba, Euphausia crystallorophias, Thysanoessa macrura) caught with a Rectangular Midwater trawl (RMT) during PS82. The volumes are in m^3

Varying dependency of Antarctic euphausiids on ice algae- and phytoplankton-derived carbon sources during summer

Sea ice algae can constitute an important carbon source for high-Antarctic euphausiids during winter. To quantify the importance of this ‘sympagic carbon’ during summer, the three most abundant Antarctic euphausiids, Euphausia superba, E. crystallorophias, and Thysanoessa macrura, collected off the Filchner Ice Shelf, were analyzed regarding their fatty acid (FA) and stable isotope compositions. Fingerprints of diatom- and dinoflagellate-associated FAs in the euphausiids indicated a mixed carbon source composition for all three species. Bulk and FA-specific carbon stable isotope compositions (δ13C) were used to quantify the contribution of sympagic carbon versus phytoplankton-produced carbon to the euphausiids’ carbon budget, suggesting a lower proportional contribution of sympagic carbon in E. superba (5–18%) compared to E. crystallorophias (16–36%) and T. macrura (15–36%). The latter two species probably received sympagic carbon through heterotrophic prey, a hitherto overlooked source of sympagic carbon for pelagic species. Euphausiids collected close to the surface indicated a higher importance of sympagic carbon to their carbon budget compared to individuals caught at greater depths. Our results imply that, in the southern Weddell Sea, ice algae play a significant, but possibly not critical role as a carbon source for the three euphausiids during summer. Their ability to utilize carbon of different origins implies a certain resilience to environmental change during summer. The winter period, however, remains the critical bottle neck of survival when Antarctic sea ice declines, because during this season of minimal pelagic productivity, ice algae standing stocks constitute the only dependable carbon source

Strong linkage of polar cod (<i>Boreogadus saida</i>) to sea ice algae-produced carbon: Evidence from stomach content, fatty acid and stable isotope analyses

International audienc

Year-round discrete underway water column Chlorophyll a concentrations from the centra Arctic

Near-daily concentrations of Chlorophyll a and phaeopigments from RV Polarsterns underway water supply system (inlet at 11m water depth) collected during legs 1,3,4, and 5 of the MOSAiC (PS122) drift expedition in the central Arctic Ocean. 2-4L of water were filtered onto pre-combusted GF/F filters (nominal pore size 0.7µm) and frozen at -80°C. Samples were subsequently extracted in 90°C acetone, homogenized using a cell mill, and measured on the following day using a Turner flourometer, followed by an acidification step to determine phaeopigments (see Knap et al. 1996 for details and calculations). Samples were collected from end of October 2019 to beginning of October 2020, with a gap between mid-December and the end of February

Dependency of Antarctic zooplankton species on ice algae‐produced carbon suggests a sea ice‐driven pelagic ecosystem during winter

How the abundant pelagic life of the Southern Ocean survives winter darkness, when the sea is covered by pack ice and phytoplankton production is nearly zero, is poorly understood. Ice‐associated (“sympagic”) microalgae could serve as a high‐quality carbon source during winter, but their significance in the food web is so far unquantified. To better understand the importance of ice algae‐produced carbon for the overwintering of Antarctic organisms, we investigated fatty acid (FA) and stable isotope compositions of 10 zooplankton species, and their potential sympagic and pelagic carbon sources. FA‐specific carbon stable isotope compositions were used in stable isotope mixing models to quantify the contribution of ice algae‐produced carbon (αIce) to the body carbon of each species. Mean αIce estimates ranged from 4% to 67%, with large variations between species and depending on the FA used for the modelling. Integrating the αIce estimates from all models, the sympagic amphipod Eusirus laticarpus was the most dependent on ice algal carbon (αIce: 54%–67%), and the salp Salpa thompsoni showed the least dependency on ice algal carbon (αIce: 8%–40%). Differences in αIce estimates between FAs associated with short‐term vs. long‐term lipid pools suggested an increasing importance of ice algal carbon for many species as the winter season progressed. In the abundant winter‐active copepod Calanus propinquus, mean αIce reached more than 50% in late winter. The trophic carbon flux from ice algae into this copepod was between 3 and 5 mg C m−2 day−1. This indicates that copepods and other ice‐dependent zooplankton species transfer significant amounts of carbon from ice algae into the pelagic system, where it fuels the food web, the biological carbon pump and elemental cycling. Understanding the role of ice algae‐produced carbon in these processes will be the key to predictions of the impact of future sea ice decline on Antarctic ecosystem functioning

The Surface and Under-Ice Trawl (SUIT)

This talk provides an overview of the technical construction and performance of SUI

Sea ice draft, surface water temperature, salinity and chlorophyl a from SUIT measurements during POLARSTERN cruise PS81

Measured surface water properties (temperature, salinity, chl a), and derived sea-ice thickness and draft for each haul. Data are interpolated on a 0.5 m grid along the transect