Strength May Lie in Numbers: Intertidal Foraminifera Non-Negligible Contribution to Surface Sediment Reworking

Abstract

The contribution of benthic foraminifera to sediment bioturbation has widely been overlooked despite their huge abundance in intertidal soft sediments. In this preliminary study, we specifically chose to focus on two key species of benthic foraminifera in temperate intertidal mudflats, Quinqueloculina seminula and Ammonia tepida, and first experimentally investigated their individual movements at the sediment surface. We subsequently derived from these observations the individual-level surface sediment reworking rates, and used the actual abundance of these species to extrapolate these rates at the population level. Individual surface sediment reworking rates SSRR i ranged between 0.13 and 0.32 cm 2 •ind −1 •day −1 for Q. seminula, and between 0.12 and 0.28 cm 2 •ind −1 •day −1 for A. tepida. Population-level surface sediment reworking rates were subsequently estimated as ranging between 11,484 and 28,710 cm 2 •m −2 •day −1 for Q. seminula and 27,876 and 65,044 cm 2 •m −2 •day −1 for A. tepida. Noticeably, these reworking rates are comparable to, and eventually even higher than, the rates reported in the literature for populations of intertidal macro-invertebrates, such as the annelid polychaete Melinna palmata and the bivalve Abra ovata. Taken together these results suggest that despite their minute size intertidal benthic foraminifera are, thanks to their abundance, non-negligible contributors to the reworking of surface sediment, and may then play an unanticipated role in the benthic ecosystem functioning, through e.g. the enhancement of fluxes at the sediment-water interface.

Effects of temperature on the behaviour and metabolism of an intertidal foraminifera and consequences for benthic ecosystem functioning

“…2 C). This is consistent with previous measurements of locomotion speed on glass petri dish, velocity being nearly twice lower at 12 °C (~ 2 mm h −1 ) 57 than at 22 °C (~ 4 mm h −1 ) 70 . This observation confirms that cold temperatures may reduce the activity of temperate foraminifera 42 .…”

Sediment reworking of intertidal sediments by the benthic foraminifera Haynesina germanica : the importance of motion behaviour and densities

“…Before running the experiments, active individuals were extracted from previously acclimated individuals then gently deposited on the sediment surface in sediment cores corresponding to LD, MD and HD treatments. Considering that living foraminifera usually start to move within a few minutes [28,32,44], a mixture of 20 mg of pink silt and 20 mg of green sand luminophores were homogeneously and gently spread on the sediment surface of each core with a Pasteur pipette one hour after foraminifera introduction.…”

“…In soft-bottom habitats, motion behaviour of intertidal foraminifera can generate horizontal displacement of sediment particles [28–30]. Some species may be involved in the vertical transport of sediment as they actively burrow in the sediment [30–32] either to reach their preferential microhabitat [33–35] or to escape after being buried by a storm or by macro-invertebrate bioturbation [36–38].…”

Foraminifera and plastic pollution: Knowledge gaps and research opportunities

“…Specifically, motion behavior is an acknowledged keystone process behind the success of foraging, mate-finding and habitat selection (Bowler and Benton 2005). Motion behavior is still, however, the forgotten child of foraminiferal ecology, despite its increasingly recognized variability Bouchet 2015, Jauffrais et al 2016) and role in bioturbation (Bouchet and Seuront 2020, Deldicq et al 2020, Deldicq et al 2021a). In addition, benthic foraminiferal behavior is affected in the presence of a stressor (gravity, organic matter, temperature; Seuront and Bouchet 2015, Jauffrais et al 2016, Deldicq et al 2021b) that may have further consequences on their search for food and for the optimal microhabitat.…”

“…They occupy a major trophic position through bacterivory, herbivory or carnivory (Nomaki et al 2008, Chronopoulou et al 2019. They also actively participate in the benthic ecosystem functioning via sediment mixing and bioirrigation, hence enhancing the fluxes of particulate and dissolved elements at the sediment-water interface (Bouchet and Seuront 2020, Deldicq et al 2020, Deldicq et al 2021a). In addition, foraminifera can accumulate large quantities of nitrate in their cell and reduce it through denitrification under low-oxygen conditions (Risgaard-Petersen et al 2006, Piña-Ochoa et al 2010; their contribution to the nitrogen cycle being, for instance, up to 70% in the North Sea (Piña-Ochoa et al 2010) or ranging from 50% to 100% in Swedish fjords (Choquel et al 2021).…”