In the SW lagoon of New Caledonia (South Pacific), the pectinid Bractechlamys vexillum (Reeve) is a characteristic species of the 1000-km² grey sand bottoms benthic community, with an average density of 1.65 ind m− 2 and a mean dorso-ventral shell height of 47 mm. To assess the role of B. vexillum populations in the transfer of matter at the water-sediment interface of the lagoon ecosystem, in situ measurements were performed of individual biodeposition of total particulate matter, particulate organic matter, particulate organic carbon and nitrogen, chlorophyll a, and pheopigments. Fluxes of particulate matter in sediment traps, with and without individuals placed in cages, were compared at various seasons (66 experiments) and related to concentrations in seston. Particulate matter biodeposit production was significantly linked to B. vexillum biomass and to suspended chlorophyll a and pheopigment concentrations, but not to temperature or to other particulate material concentrations in seston. Daily average biodeposit production of total particulate matter and particulate organic carbon by unit of biomass were 298 mg g AFDW− 1 d− 1 and 45 mg g AFDW− 1 d− 1, respectively. At the study site, biodeposition by the B. vexillum population was 570 mg m− 2 d− 1 of total particulate matter and 68 mg m− 2 d− 1 of organic carbon, which represent 4.8% and 6.4% of natural sedimentation, respectively. This relatively low figure at the local scale results, however, in a total contribution of B. vexillum to particulate sedimentation in the whole lagoon of 34 * 103 metric tons year− 1 for total particulate matter and 4 * 103 metric tons year− 1 for organic carbon.