Microphytobenthos (MPB) represents an important food source for primary consumers in estuarine ecosystems and the availability of MPB as food items results from complex physical, chemical, and biological interactions. In Baie des Veys (Lower Normandy, France), the common cockle Cerastoderma edule constitutes the major bioturbator in the ecosystem in terms of biomass. In this ecosystem, cockle bioturbation is a key process regulating the MPB erosion flux in the water column. This bivalve intensely modifies the top layer of the sediment by increasing the sediment erodibility and the fluxes of suspended chlorophyll a through the valve movements. More precisely, cockle bioturbation destabilizes the sediment surface by creating a biogenic layer that is easily eroded with tidal hydrodynamic forces. Associated MPB can then be exported to the water column to fuel higher trophic levels of the planktonic food web. The aim of this study was to develop a numerical model that reproduces the export of MPB associated to the biogenic layer erosion. Kinetics of suspended MPB, in response to increasing stress, were obtained from flume experiments in lab controlled conditions and in situ natural conditions. Following this, the suspended MPB were analyzed to respectively parameterize the model by 1) a calibration approach, and 2) an independent validation. The analysis has highlighted that the higher the biomass of cockles, the higher the MPB resuspension rates. Our model consistently reproduces the tendency encountered in laboratory analysis and with in situ natural conditions. During the validation, a small site-specific lack of adjustment was identified, but, among the macrozoobenthic community, the model can be significantly improved by considering the bioturbation activities of another ecosystem engineer, Pygospio elegans. This study thus provides reliable estimates of the daily food availability from benthic primary consumers in an estuarine system where cockles dominate the bioturbating assemblage. This model can be inserted in various model designs (0D, 1Dvertical or 3D).

Post‐settlement dispersal is a key process in the recruitment of bivalves. To assess the role of such secondary migrations and to identify potential associated triggers, we conducted an in situ sampling survey during the summer recruitment period on the bivalve assemblages of a coarse‐sediment temperate tidal habitat in the Chausey archipelago (Normandy, France). The dynamics of drifters were studied using three types of settler traps (for example, bedload, pelagic, and sinking transports), and we monitored both the abiotic (hydrological and hydrodynamic conditions) and the trophic (nano‐ and pico‐sized particulate organic matter [POM]; fatty acid composition of POM and sediment organic matter [SOM]) environmental parameters. Such an approach allows the discrimination of passive migration (due to sediment erosion by tidal currents and waves) from active migration (related to recruit behavior). Secondary migrations were observed in 25 bivalve taxa, and these mainly involved decreasing abundances of Mytilidae, Nuculidae, Semelidae, Mactridae, and Lucinidae individuals on the study site, highlighting the crucial role of these processes in highly dynamic coastal benthic assemblages. Surprisingly, the intense post‐settlement dispersal observed at the end of the recruitment season was not synchronized with periods of high hydrodynamic stress but to a change in the structure of phytoplanktonic assemblages, particularly the nanoeukaryotic component. Such a response by bivalve recruits to a trophic pelagic cue—triggering secondary migrations—could result from an increased demand for energy required for active migratory behavior.