Schweizer Magali

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Schweizer
First Name
Magali
ORCID
0000-0001-5115-1616

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  • Preprint
    Ultrastructure and distribution of kleptoplasts in benthic foraminifera from shallow-water (photic) habitats
    ( 2017-10) Jauffrais, Thierry ; LeKieffre, Charlotte ; Koho, Karoliina ; Tsuchiya, Masashi ; Schweizer, Magali ; Bernhard, Joan M. ; Meibom, Anders ; Geslin, Emmanuelle
    Assimilation, sequestration and maintenance of foreign chloroplasts inside an organism is termed “chloroplast sequestration” or “kleptoplasty”. This phenomenon is known in certain benthic foraminifera, in which such kleptoplasts can be found both intact and functional, but with different retention times depending on foraminiferal species. In the present study, seven species of benthic foraminifera (Haynesina germanica, Elphidium williamsoni, E. selseyense, E. oceanense, E. aff. E. crispum, Planoglabratella opercularis and Ammonia sp.) were collected from shallow-water benthic habitats and examined with transmission electron microscope (TEM) for cellular ultrastructure to ascertain attributes of kleptoplasts. Results indicate that all these foraminiferal taxa actively obtain kleptoplasts but organized them differently within their endoplasm. In some species, the kleptoplasts were evenly distributed throughout the endoplasm (e.g., H. germanica, E. oceanense, Ammonia sp.), whereas other species consistently had plastids distributed close to the external cell membrane (e.g., Elphidium williamsoni, E. selseyense, P. opercularis). Chloroplast degradation also seemed to differ between species, as many degraded plastids were found in Ammonia sp. and E. oceanense compared to other investigated species. Digestion ability, along with different feeding and sequestration strategies may explain the differences in retention time between taxa. Additionally, the organization of the sequestered plastids within the endoplasm may also suggest behavioral strategies to expose and/or protect the sequestered plastids to/from light and/or to favor gas and/or nutrient exchange with their surrounding habitats.
  • Article
    Deposit-feeding of Nonionellina labradorica (foraminifera) from an Arctic methane seep site and possible association with a methanotroph
    (European Geosciences Union, 2022-08-30) Schmidt, Christiane ; Geslin, Emmanuelle ; Bernhard, Joan M. ; LeKieffre, Charlotte ; Svenning, Mette Marianne ; Roberge, Hélène ; Schweizer, Magali ; Panieri, Giuliana
    Several foraminifera are deposit feeders that consume organic detritus (dead particulate organic material with entrained bacteria). However, the role of such foraminifera in the benthic food web remains understudied. Foraminifera feeding on methanotrophic bacteria, which are 13C-depleted, may cause negative cytoplasmic and/or calcitic δ13C values. To test whether the foraminiferal diet includes methanotrophs, we performed a short-term (20 h) feeding experiment with Nonionellina labradorica from an active Arctic methane-emission site (Storfjordrenna, Barents Sea) using the marine methanotroph Methyloprofundus sedimenti and analysed N. labradorica cytology via transmission electron microscopy (TEM). We hypothesised that M. sedimenti would be visible post-experiment in degradation vacuoles, as evidenced by their ultrastructure. Sediment grains (mostly clay) occurred inside one or several degradation vacuoles in all foraminifers. In 24 % of the specimens from the feeding experiment degradation vacuoles also contained bacteria, although none could be confirmed to be the offered M. sedimenti. Observations of the apertural area after 20 h incubation revealed three putative methanotrophs, close to clay particles, based on bacterial ultrastructural characteristics. Furthermore, we noted the absence of bacterial endobionts in all examined N. labradorica but confirmed the presence of kleptoplasts, which were often partially degraded. In sum, we suggest that M. sedimenti can be consumed via untargeted grazing in seeps and that N. labradorica can be generally classified as a deposit feeder at this Arctic site.
  • Article
    Foraminiferal Mn/Ca as bottom-water hypoxia proxy: an assessment of Nonionella stella in the Santa Barbara Basin, USA
    (American Geophysical Union, 2021-10-18) Brinkmann, Inda ; Ni, Sha ; Schweizer, Magali ; Oldham, Véronique E. ; Quintana Krupinski, Nadine B. ; Medjoubi, Kadda ; Somogyi, Andrea ; Whitehouse, Martin J. ; Hansel, Colleen M. ; Barras, Christine ; Bernhard, Joan M. ; Filipsson, Helena L.
    Hypoxia is of increasing concern in marine areas, calling for a better understanding of mechanisms leading to decreasing dissolved oxygen concentrations ([O2]). Much can be learned about the processes and implications of deoxygenation for marine ecosystems using proxy records from low-oxygen sites, provided proxies, such as the manganese (Mn) to calcium (Ca) ratio in benthic foraminiferal calcite, are available and well calibrated. Here we report a modern geochemical data set from three hypoxic sites within the Santa Barbara Basin (SBB), USA, where we study the response of Mn/Caforam in the benthic foraminifer Nonionella stella to variations in sedimentary redox conditions (Mn, Fe) and bottom-water dissolved [O2]. We combine molecular species identification by small subunit rDNA sequencing with morphological characterization and assign the SBB N. stella used here to a new phylotype (T6). Synchrotron-based scanning X-ray fluorescence (XRF) imaging and Secondary Ion Mass Spectrometry (SIMS) show low Mn incorporation (partition coefficient DMn < 0.05) and limited proxy sensitivity of N. stella, at least within the range of dissolved [O2] (2.7–9.6 μmol/l) and Mnpore-water gradients (2.12–21.59 μmol/l). Notably, even though intra- and interspecimen Mn/Ca variability (33% and 58%, respectively) was only partially controlled by the environment, Mn/Caforam significantly correlated with both pore-water Mn and bottom-water [O2]. However, the prevalent suboxic bottom-water conditions and limited dissolved [O2] range complicate the interpretation of trace-elemental trends. Additional work involving other oxygenation proxies and samples from a wider oxygen gradient should be pursued to further develop foraminiferal Mn/Ca as an indicator for hypoxic conditions.
  • Article
    Through the eDNA looking glass: Responses of fjord benthic foraminiferal communities to contrasting environmental conditions
    (Wiley, 2023-03-27) Brinkmann, Inda ; Schweizer, Magali ; Singer, David ; Quinchard, Sophie ; Barras, Christine ; Bernhard, Joan M. ; Filipsson, Helena L.
    The health of coastal marine environments is severely declining with global changes. Proxies, such as those based on microeukaryote communities, can record biodiversity and ecosystem responses. However, conventional studies rely on microscopic observations of limited taxonomic range and size fraction, missing putatively ecologically informative community components. Here, we tested molecular tools to survey foraminiferal biodiversity in a fjord system (Sweden) on spatial and temporal scales: Alpha and beta diversity responses to natural and anthropogenic environmental trends were assessed and variability of foraminiferal environmental DNA (eDNA) compared to morphology‐based data. The identification of eDNA‐obtained taxonomic units was aided by single‐cell barcoding. Our study revealed wide diversity, including typical morphospecies recognized in the fjords, and so‐far unrecognized taxa. DNA extraction method impacted community composition outputs significantly. DNA extractions of 10 g sediment more reliably represented present diversity than of 0.5‐g samples and, thus, are preferred for environmental assessments in this region. Alpha‐ and beta diversity of 10‐g extracts correlated with bottom‐water salinity similar to morpho‐assemblage diversity changes. Sub‐annual environmental variability resolved only partially, indicating damped sensitivity of foraminiferal communities on short timescales using established metabarcoding techniques. Systematically addressing the current limitations of morphology‐based and metabarcoding studies may strongly improve future biodiversity and environmental assessments.
  • Article
    Benthic foraminiferal Mn/Ca as low‐oxygen proxy in Fjord sediments
    (American Geophysical Union, 2023-05-03) Brinkmann, Inda ; Barras, Christine ; Jilbert, Tom ; Paul, K. Mareike ; Somogyi, Andrea ; Ni, Sha ; Schweizer, Magali ; Bernhard, Joan M. ; Filipsson, Helena L.
    Fjord systems are typically affected by low‐oxygen conditions, which are increasing in extent and severity, forced by ongoing global changes. Fjord sedimentary records can provide high temporal resolution archives to aid our understanding of the underlying mechanisms and impacts of current deoxygenation. However, such archives can only be interpreted with well‐calibrated proxies. Bottom‐water oxygen conditions determine redox regime and availability of redox‐sensitive trace elements such as manganese, which in turn may be recorded by manganese‐to‐calcium ratios (Mn/Ca) in biogenic calcium carbonates (e.g., benthic foraminifera tests). However, biological influences on Mn incorporation (e.g., species‐specific Mn fractionation, ontogeny, living and calcification depths) are still poorly constrained. We analyzed Mn/Ca of living benthic foraminifera (Bulimina marginata, Nonionellina labradorica), sampled at low‐ to well‐oxygenated conditions over a seasonal gradient in Gullmar Fjord, Swedish West coast (71–217 μmol/L oxygen (O2)), by laser‐ablation ICP‐MS. High pore‐water Mn availability in the fjord supported Mn incorporation by foraminifera. B. marginata recorded contrasting Mn redox regimes sensitively and demonstrated potential as proxy for low‐oxygen conditions. Synchrotron‐based scanning X‐ray fluorescence nanoimaging of Mn distributions across B. marginata tests displayed Mn/Ca shifts by chambers, reflecting bottom‐water oxygenation history and/or ontogeny‐driven life strategy preferences. In contrast, Mn/Ca signals of N. labradorica were extremely high and insensitive to environmental variability. We explore potential biologically controlled mechanisms that could potentially explain this species‐specific response. Our data suggest that with the selection of sensitive candidate species, the Mn/Ca proxy has potential to be further developed for quantitative oxygen reconstructions in the low‐oxygen range.