Knowledge of the trophic position of meiofauna in marine sediments is still contradictory primarily due to the scarcity of experimental data. The present study analyses diatom-feeders among the meiofauna. The assimilation rate of carbon by meiofauna was determined through a grazing experiment using in situ collected diatoms pre-labelled with 14 C. The assimilation rates of diatom carbon were estimated for the bulk meiofaunal community (0.84 ng C.ind −1 .h −1), for the bulk harpacticoid copepods (1.92 ng C.ind. −1 h −1) and for two dominant nematode species (Metachromadora remanei 1.26 ng C ind −1 h −1 , Daptonema oxycerca 1.35 ngC.ind. −1 h −1). Experimental results were extrapolated to compute the consumption of meiofauna in situ that would attain up to 12% of primary benthic production in the Brouage mudflat (Marennes-Oléron Bay, southwest Atlantic coast).