10 Nov 2021
10 Nov 2021
Status: a revised version of this preprint is currently under review for the journal BG.

Deposit feeding of a foraminifera from an Arctic methane seep site and possible association with a methanotroph revealed by transmission electron microscopy

Christiane Schmidt1,2,3, Emmanuelle Geslin1, Joan M. Bernhard4, Charlotte LeKieffre1,5, Mette Marianne Svenning2,6, Helene Roberge1,7, Magali Schweizer1, and Giuliana Panieri2 Christiane Schmidt et al.
  • 1LPG, Laboratoire de Planétologie et de Géodynamique, Univ. Angers, Université de Nantes, CNRS, LPG, SFR QUASAV, Angers, 49000, France
  • 2CAGE, Centre for Arctic Gas Hydrate, Environment and Climate, UiT, The Arctic University of Norway, Tromsø, 9010, Norway
  • 3ZMT, Leibniz Centre for Tropical Marine Research, Bremen, 28359, Germany
  • 4Woods Hole Oceanographic Institution, Geology & Geophysics Department, Woods Hole, 02543, MA, USA
  • 5Cell and Plant Physiology Laboratory, CNRS, CEA, INRAE, IRIG, Université Grenoble Alpes, Grenoble, 38054, France
  • 6Department of Arctic and Marine Biology, UiT, The Arctic University of Norway, Tromsø, 9037, Norway
  • 7Université de Nantes, CNRS, Institut des Matériaux Jean Rouxel, IMN, Nantes, 44000, France

Abstract. Several foraminifera are deposit feeders that consume organic detritus (dead particulate organic material along with entrained bacteria). However, the role of such foraminifera in the benthic food-web remains understudied. As foraminifera may associate with methanotrophic bacteria, which are 13C-depleted, feeding on them has been suggested to cause negative δ13C values in the foraminiferal cytoplasm and/or calcite. To test whether the foraminiferal diet includes methanotrophs, we performed a short-term (1 d) feeding experiment with Nonionellina labradorica from an active Arctic methane-emission site (Storfjordrenna, Barents Sea) using the marine methanotroph Methyloprofundus sedimenti, and analyzed N. labradorica cytology via Transmission Electron microscopy (TEM). We hypothesized that M. sedimenti would be visible, as evidenced by their ultrastructure, in degradation vacuoles after this feeding experiment. 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 area adjacent to the aperture after 20 h incubation revealed three putative methanotrophs, close to clay particles. These methanotrophs were identified based on internal characteristics such as a type I stacked intracytoplasmic membranes (ICM), storage granules (SG) and gram-negative cell walls (GNCW). Furthermore, N. labradorica specimens were examined for specific adaptations to this active Arctic methane-emission site; we noted the absence of bacterial endobionts in all specimens examined but confirmed the presence of kleptoplasts, which were often partially degraded. Based on these observations, we suggest that M. sedimenti can be consumed by N. labradorica via untargeted grazing in seeps and that N. labradorica can be generally classified as a deposit feeder at this Arctic site. These results suggest that if methanothrophs are available to the foraminifera in their habitat, their non-selective uptake could make a substantial contribution to altering δ13Ctest values. This in turn may impact metazoans grazing on benthic foraminifera by altering their δ13C signature.

Christiane Schmidt et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-284', Jutta Wollenburg, 22 Nov 2021
    • AC1: 'Reply on RC1', Christiane Schmidt, 04 Mar 2022
  • RC2: 'Comment on bg-2021-284', Anonymous Referee #2, 03 Dec 2021
    • AC2: 'Reply on RC2', Christiane Schmidt, 04 Mar 2022
  • RC3: 'Comment on bg-2021-284', Anonymous Referee #3, 07 Dec 2021
    • AC3: 'Reply on RC3', Christiane Schmidt, 04 Mar 2022

Christiane Schmidt et al.

Christiane Schmidt et al.


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Short summary
This study's main objective was to better understand the feeding habits of benthic foraminifera around an active methane seepage site. For this we carried out a feeding experiment with a marine methanotroph to examine uptake and cell ultrastructure using transmission electron microscopy (TEM). The results revealed three putative methanotrophs as the outside of the cell/test, which could be taken up via untargeted grazing in seeps. We conclude that this species is a non-selective deposit feeder.