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

Vincent M P Bouchet,Laurent Seuront

doi:10.4236/ojms.2020.103010

Vincent M P Bouchet, Laurent Seuront

Open Access

https://doi.org/10.4236/ojms.2020.103010

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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 SSRRi ranged between 0.13 and 0.32 cm2·ind-1·day-1 for Q. seminula, and between 0.12 and 0.28 cm2·ind-1·day-1 for A. tepida. Population-level surface sediment reworking rates were subsequently estimated as ranging between 11,484 and 28,710 cm2·m-2·day-1 for Q. seminula and 27,876 and 65,044 cm2·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.

Highlights

Benthic fauna typically influences the structure and function of soft-sediment benthic ecosystems through bioturbation, that is the biogenic modification of sediments through particle reworking and burrow ventilation; see [1] for a review
We 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
In situ abundances of Quinqueloculina seminula and Ammonia tepida were subsequently used to scale the individual SSRRi up to a surface unit of 1 m2 as a population-level surface sediment reworking rate SSRRp. Both Quinqueloculina seminula and Ammonia tepida drastically modified the initially smooth and undisturbed sediment surface (Figure 1(A)) where they typically created intense networks of sinuous trails surrounded by a fluffy layer of sediment (Figure 1(B))

Summary

Introduction

Benthic fauna typically influences the structure and function of soft-sediment benthic ecosystems through bioturbation, that is the biogenic modification of sediments through particle reworking and burrow ventilation; see [1] for a review. Benthic foraminifera are able to migrate down through the sediment, up to a depth of 4 cm for Quinqueloculina impressa [17] This process leads to the construction of biogenic structures, such as networks of galleries for Q. impressa [17] and cavities for Elphidium excavatum clavatum [20] [21]. These biogenic structures contribute to a better oxygenation of the surface layer [22] and determine the fluxes of both particulate and dissolved materials at the sediment-water interface as in benthic macrofauna [1]. This is, still an open question as only one study quantified bioturbation by benthic foraminifera [23]

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