21 Sep 2023
 | 21 Sep 2023
Status: a revised version of this preprint is currently under review for the journal BG.

Potential impacts of cable bacteria activity on hard-shelled benthic foraminifera: a prelude to implications for their interpretation as bioindicators or paleoproxies

Maxime Daviray, Emmanuelle Geslin, Nils Risgaard-Petersen, Vincent V. Scholz, Marie Fouet, and Edouard Metzger

Abstract. Cable bacteria (CB) are filamentous bacteria coupling sulphide oxidation to oxygen reduction over centimetre distances. This bacterial activity generates a strong pH gradient within the first few centimetres of the sediment that affects the microhabitats occupied by benthic foraminifera. Hard-shelled foraminifera are protists able to build a calcareous or agglutinated shell (called “test”). Here we study the impact of sediment acidification induced by CB activity (CBA) on calcareous test preservation. For this study, sediment cores were sampled in the macrotidal Auray estuary located on the French Atlantic coast. Living and dead foraminifera were quantified (until 5-cm depth) and discriminated using the Cell-TrackerTM Green vital marker. CBA was assessed with pH and oxygen profiles combined with quantitative Polymerase Chain Reaction (q-PCR). On two different intertidal mudflats, volumetric filament densities have been measured. They were comparable to those observed in the literature for coastal environments, with 7.4 ± 0.4 and 74.4 ± 5.0−3 per bulk sediment respectively. Highly contrasting CBA (from low to very intense) were described with lowest pH at 5.8. This seems to lead to various dissolution stages of the foraminiferal calcareous test from intact to fully dissolved tests revealing the organic lining. The dissolution scale is based on observations of living Ammonia spp. and Haynesina germanica specimens under a Scanning Electronic Microscope. Furthermore, dead foraminiferal assemblages showed a strong calcareous test loss and an organic lining accumulation throughout depth under low pH, hampering the test preservation in deep sediment. These changes in both living and dead foraminiferal assemblages imply that CB must be strongly considered in ecological monitoring and historical studies using foraminifera as bioindicator and paleoenvironmental proxy.

Maxime Daviray 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-2023-169', Sebastiaan van de Velde, 26 Sep 2023
    • AC1: 'Reply on RC1', Maxime Daviray, 03 Nov 2023
  • RC2: 'Comment on bg-2023-169', Anonymous Referee #2, 19 Oct 2023
    • AC3: 'Reply on RC2', Maxime Daviray, 20 Nov 2023
  • RC3: 'Comment on bg-2023-169', Anonymous Referee #3, 30 Oct 2023
    • AC2: 'Reply on RC3', Maxime Daviray, 08 Nov 2023

Maxime Daviray et al.

Maxime Daviray et al.


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Short summary
Coastal marine sediments are subject to major acidification processes because of climate change and human activities, but these processes can also result from biotic activity. We studied the cable bacteria activity effect on benthic calcareous foraminifera in intertidal mudflats. The strong pH decrease in sediments caused by these bacteria leads to the calcareous test dissolution of living and dead foraminifera, threatening the test preservation and their robustness as bioindicators or proxies.