Tidal flats are biogeomorphic landscapes, shaped by physical forces and interaction with benthic biota. We used a metabolic approach to assess the overarching effect of bioturbators on tidal landscapes. The benthic bivalve common cockle (Cerastoderma edule) was used as model organism. The effect of C. edule on sediment resuspension was approximated as a function of the overall population metabolic rate per unit of area. We combined i) laboratory observations on how C. edule affect sediment resuspension along gradients of bioturbation activity, sediment cohesiveness and hydrodynamic force with ii) spatial data on the natural distribution of intertidal C. edule populations. This allowed us to build an integrated model of the C. edule effect on sediment resuspension along the tidal gradient. Owing to the temperature dependence of metabolic rate, the model also accounted for seasonal variation in bioturbators activity. Laboratory experiments indicated that sediment resuspension is positively related to the metabolic rate of the C. edule population especially in cohesive sediments. Based on this observation, we predicted a clear spatial and seasonal pattern in the relative importance of C. edule contribution to sediment resuspension along a tidal transect. At lower elevations, our model indicates that hydrodynamics overrules biotic effects; at higher elevations, inter-tidal hydrodynamics should be too low to suspend bioturbated sediments. The influence of C. edule on sediment resuspension is expected to be maximal at the intermediate elevation of a mudflat, owing to the combination of moderate hydrodynamic stress and high bioturbator activity. Also, bio-mediated sediment resuspension is predicted to be particularly high in the warm season. Research into metabolic dependency of bio-mediated sediment resuspension may help to place phenomenological observations in the broader framework of metabolic theories in ecology and to formulate general expectations on the coastal ecosystem functioning.

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Predictive models accounting for the effect of bioturbation on sediment resuspension must be based on ecological theory as well as on empirical parametrizations. The scaling trend of individual metabolic and activity rates with body mass may be a key to the mechanistic understanding of the observed patterns. With this study we tested if general size scaling rules in bio-mediated sediment resuspension may apply to a broad range of physical contexts for the endobenthic bivalve Cerastoderma edule. The effect on sediment resuspension of populations of C. edule differing by individual size was measured across physical gradients of current velocity and sediment composition in terms of fraction of fine particles. C. edule were able to enhance the resuspension of sediment containing silt, while they had scarce effect on the resuspension of coarse sediment. The effect of bioturbation was maximal at intermediate current velocity, when the hydrodynamic forcing is not strong enough to overcome the abiotic sediment resistance but it is able to suspend the bioturbated sediment. Although differences in sediment silt content and intensities of hydrodynamic stress have a relevant influence in determining the bioturbators individual contribution to sediment resuspension, the observed mass scaling trend is consistent across all treatments and close to theoretical expectation for size scaling of individual metabolic rates. This observation supports the hypothesis that the contribution of individual bioturbators to sediment resuspension is directly related to their energy use. Therefore, the proposed approach allows the formulation of expectations of biotic contribution to sediment resuspension based on the general size scaling laws of individual energy use.@en

The Eastern Scheldt, a tidal basin in the southwest of The Netherlands, underwent large physical and ecological changes due to a system-wide human interference. The construction of a storm surge barrier at the seaward side and closure of the upstream branches in the 1980s resulted in intertidal flat erosion. This has far reaching consequences for the ecological functioning of these habitats, especially as foraging ground for many wader species. Therefore, a 1.3 million m3 sand nourishment is foreseen on the Roggenplaat intertidal shoal to mitigate the erosion and preserve suitable foraging habitat for waders for the coming 25 years. This paper presents an integral nourishment design approach. It consists of the following steps: (i) understanding the morphology and ecology, (ii) translation of the nourishment objective into an evaluation framework, (iii) construction of a suitability map indicating potential nourishment locations, (iv) generation of nourishment designs, (v) short-term morphodynamic numerical model simulations, (vi) estimation of the long-term shoal development using a simplified approach, (vii) integral evaluation leading to the preferred design. This integral approach resulted in a design that is expected to fulfill the Roggenplaat nourishment objective, accounting for ecological, morphological, economical and technical aspects. This integrated approach could form a basis for future intertidal shoal nourishment designs worldwide.@en