In atoll lagoons of French Polynesia, growth and reproduction of pearl oysters are mainly driven by plankton concentration. However, the actual diet of black-lip pearl oysters P. margaritifera in these lagoons is poorly known. To fill this gap, we used the flow through chamber method to measure clearance rates of P. margaritifera in Ahe atoll lagoon (Tuamotu Archipelago, French Polynesia). We found : (i) that pearl oysters cleared plankton at a rate that was positively related to plankton biovolume, (ii) that nanoflagellates were the main source of carbon for the pearl oysters, (iii) that the quantity and origin of carbon filtrated by pearl oysters was highly dependent on the concentration and composition of plankton. These results provide essential elements for the comprehension of growth and reproduction variability of pearl oysters in atoll lagoons of French Polynesia.