The density and species composition of the nematode assemblage was investigated in the Brouage mudflat (Marennes-Ole´ron, France) at three stations over four seasons in relation to environmental parameters (organic matter percentage, chlorophyll a and heavy metal content). From the 43 species recorded, six dominant genera represented 75% of the assemblage. Fluctuations of these species were mainly in response to the observed temporal patterns. Over the course of a year, epigrowth feeders were the most important trophic group (43%) with three dominant species Metachromadoroides remanei, Chromadora macrolaima and Ptycholaimellus jacobi but some non-selective deposit feeders, notably Daptonema oxycerca, also contributed to the utilisation of primary production. The feeding strategies of the dominant species particularly for epistrate feeders are discussed. An assessment of the influence of nematodes grazing on microphytobenthos biomass and production was then performed. Comparison of nematode species grazing rates based on nematode abundance and ingestion rates and microphytobenthic production are discussed. Using the trophic structure of nematode populations to extend those results, grazing rates represent a significant part of microphytobenthic production in springtime.