Sediment stability: can we disentangle the effect of bioturbating species on sediment erodibility from their impact on sediment roughness?
|Author(s)||Dairain Annabelle1, 3, Maire Olivier2, Meynard Guillaume1, Richard Anaïs2, Rodolfo-Damiano Tiffany2, Orvain Francis1|
|Affiliation(s)||1 : Unité Biologie des ORganismes et Ecosystèmes Aquatiques (FRE BOREA), Sorbonne Universités, Muséum National d'Histoire Naturelle, CNRS, Université Pierre et Marie Curie, Université de Caen Normandie, IRD 207, Université des Antilles, Esplanade de la paix, F-14032, Caen, France
2 : Univ. Bordeaux, EPOC, UMR CNRS 5805, 2 rue du Pr Jolyet, F-33120, Arcachon, France
3 : Marine Biology Research Group, Department of Biology, Ghent University, Krijgslaan 281/S8, Ghent, 9000, Belgium
|Source||Marine Environmental Research (0141-1136) (Elsevier BV), 2020-12 , Vol. 162 , P. 105147 (13p.)|
|WOS© Times Cited||8|
|Keyword(s)||Cerastoderma edule, Sediment erodibility, Bioturbation, Bed roughness, Microphytobenthos, Density-dependent effect, Suspended-food availability|
Benthic organisms, in particular bioturbators, can influence erosion processes either by affecting sediment roughness through their mere presence and/or activities, or by modulating sediment characteristics (e.g., silt content, granulometry) and thus altering its erodibility. To date, it was not possible to distinguish the influence of bioturbating species on sediment roughness from their impact on sediment erodibility. Consequently, uncertainties remain regarding the role played by benthic species on sediment dynamics. In this study, we used a canal flume which allows to record the bed shear stress at the surface of a non-cohesive sediment (4% of mud) during erosion experiments, thus allowing to disentangle the influence of bioturbators, here the common cockle Cerastoderma edule, on the two erosion mechanisms. In order to assess the influence of bioturbating species on sediment stability in different environmental situations, we additionally tested for the effects of three factors, i.e. bivalve density, availability of suspended food (i.e. phytoplankton presence) and microphytobenthos (MPB) occurrence, which may modulate the behavior of cockles. We observed that cockles promote the erosion of the surficial layer by increasing its roughness as a consequence of their sediment reworking activity and/or presence at the sediment surface (emerging shell). In contrast, we calculated similar critical bed shear stress for erosion with and without bivalves suggesting that cockles have a minor influence on the erodibility of non-cohesive substrates with a low silt content. The destabilizing effect of cockles increased with the bivalve density whereas it was attenuated by the presence of phytoplankton. We hypothesize that the magnitude of cockles' bioturbation activity was lower when a high proportion of suspended food is available. High concentrations of suspended food may also have enhanced the filtration and biodeposition rates of cockles, thus rapidly leading to the ‘muddification’ of the sediment bed and consequently counteracting with the own destabilizing effect of the bivalves. Finally, the sole presence of MPB did not significantly affect the resuspension dynamics of non-cohesive sediments with a low proportion of mud.