Effects of bioturbation on the erodibility of cohesive versus non-cohesive sediments along a current-velocity gradient: A case study on cockles
Li, B.; Cozzoli, F.; Soissons, L.M.; Bouma, T.J.; Chen, L. (2017). Effects of bioturbation on the erodibility of cohesive versus non-cohesive sediments along a current-velocity gradient: A case study on cockles. J. Exp. Mar. Biol. Ecol. 496: 84-90. https://dx.doi.org/10.1016/j.jembe.2017.08.002
In: Journal of Experimental Marine Biology and Ecology. Elsevier: New York. ISSN 0022-0981; e-ISSN 1879-1697, more
Soft-bottom bioturbators are ecosystem engineers in the sense that they can have considerable effects on sedimenterodibility and resuspension. The common cockle Cerastoderma edule is a bioturbating filter feeder that iswidespread along the European Atlantic coastline. Its presence and activity can decrease sediment erosionthresholds in cohesive sediments but little is known about its effect on non-cohesive sediments. Using controlledannular flume experiments, we investigated the relative effects of different cockle densities on sediment resuspensionin cohesive vs. non-cohesive sediments by assessing the following: (i) the mud and sand burrowingbehavior of cockles, (ii) critical erosion thresholds, (iii) the mass of eroded sediment and (iv) erosion rates. Ourresults show that cockles were more active in non-cohesive sediment compared with cohesive sediment. Despitetheir lower activity, the presence of cockles in cohesive sediment increased sediment erodibility by reducing thecritical erosion threshold (Ucrit) and increasing both the mass of eroded sediment and erosion rate. In contrast,cockles had no effect on erodibility in non-cohesive sediment, especially on the eroded sediment mass anderosion rate. The mass eroded was not significantly different between cohesive and non-cohesive sedimentswhen cockles were present. Our experiments show that the increased erodibility of cohesive sediment due to thebioturbation by cockles is density dependent: higher cockle density results in stronger effects on erodibility.Moreover, this increase in cohesive sediment erosion due to cockle bioturbation was positively correlated withcurrent velocity. In contrast, the erosion of non-cohesive sediment only depended on the current stress and wasunaffected by cockle density. Considering the high abundance of C. edule, its widespread distribution and itsextensive activities, the results of this study could be widely applicable to intertidal mud flats around the world.
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