Meiofauna improve oxygenation and accelerate sulfide removal in the seasonally hypoxic seabed

Abstract

Oxygen depleted areas are widespread in the marine realm. Unlike macrofauna, meiofauna are abundant in hypoxic sediments. We studied to what extent meiofauna affect oxygen availability, sulfide removal and microbial communities. Meiofauna were extracted alive and added to intact sediments simulating abundance gradients previously reported in the area. A total of 324 porewater microprofiles were recorded over a 3-week incubation period and microbial community structure and cable bacteria densities were determined at the end of the experiment. At high abundances meiofauna activity deepened oxygen penetration by 85%, 59%, and 62% after 5, 14, and 22 days, respectively, compared to control sediment with scarce meiofauna. After 6 days, meiofauna increased the volume of oxidized, sulfide-free sediment by 68% and reduced sulfide fluxes from 8.8 to 0.4 mmol m −2 d −1 . After 15 days, the difference with the control attenuated due to the presence of a cable bacteria population, which facilitated sulfides oxidation in all treatments. 16S rRNA gene analysis revealed that meiofauna affected microbial community structure (beta diversity). Thus, meiofauna bioturbation plays an important role in deepening oxygen penetration, counteracting euxinia and in structuring microbial diversity of hypoxic sediments. Co-existence with cable bacteria demonstrates neutralism interaction between these two ecosystem engineers.

Coupled dynamics of iron, manganese, and phosphorus in brackish coastal sediments populated by cable bacteria

“…However, meiofauna can be abundant in Baltic Sea sediment (Broman et al 2020 ) and could thus impact the cycling of Fe and Mn, by deepening O 2 penetration. Meiofauna can possibly coexist with cable bacteria (Bonaglia et al 2020 ). At site JML, the lack of O 2 will have hindered cable bacteria activity (Burdorf et al 2018 ) and the presence of ΣH 2 S in the bottom water during part of the year will have prevented the formation and preservation of Fe and Mn oxides.…”

Inter-specific and inter-individual trait variability matter in surface sediment reworking rates of intertidal benthic foraminifera

“…For instance, in an intertidal mudflat, nematode displacements have been shown to stimulate microphytobenthos accumulation in the surface biofilm leading to a shift in diatom community (D'Hondt et al 2018). Taken together, these observations strongly suggest that the role of meiofauna in bioturbation processes needs to be urgently considered in studies dealing with benthic ecosystem functioning as they play an important role in soft sediment ecosystems (Näslund et al 2010;Nascimento et al 2012;Bonaglia et al 2014Bonaglia et al , 2020.…”

“…Sediment particle reworking typically drives (i) substrate physical properties such as granulometry and erodibility and (ii) bacterial communities (Orvain et al 2003(Orvain et al , 2004. This process affects chemical gradients and increases dissolved fluxes at the sediment-water interface (Orvain et al 2004;Kristensen et al 2012;Schratzberger and Ingels 2018;Bonaglia et al 2020). Overall, bioturbation contributes to the mineralisation of organic matter; thereby enhancing carbon and nutrient cycling (Aller 1994;Mermillod-Blondin and Rosenberg 2006;Meysman et al 2006;Kristensen et al 2012).…”

“…They also affect the oxygen penetration depth, increasing solute transport (e.g. sulphides) into the sediment (Aller and Aller 1992;Rysgaard et al 2000;Bonaglia et al 2020). For instance, in an intertidal mudflat, nematode displacements have been shown to stimulate microphytobenthos accumulation in the surface biofilm leading to a shift in diatom community (D'Hondt et al 2018).…”

“…These observations highlighted the non-negligible importance of benthic foraminifera to contribute to sediment reworking processes. Furthermore, meiofauna (including foraminifera) can increase rate of solute transport and stimulate aerobic decomposition and nitrification processes in the oxic zone (Aller and Aller 1992;Aller 1994;Bonaglia et al 2020).…”