Two phenomena control the rate of sedimentation of planktic foraminifers: (1) changes in the populations structure with time; and (2) size-dependent settling velocities of empty shells. As a result, the total flux and the flux per-size-fraction change significantly during a reproductive cycle. This implies that timing and duration of collection of trap devices are important parameters for interpreting sediment trap-collected samples. Using data on the distribution and abundance of living Globigerinoides sacculifer (Brady) from the central Red Sea, a shell flux was modelled. The simulations demonstrate that the sedimentation pattern oscillates on a lunar basis. The foremost result of this study is that the timing of trap deployment within the lunar cycle does not influence the collection if the deployment time of the trap is equal to or a multiple of the reproductive cycle. The effect of two variables on the daily calcite flux was investigated: (1) the reproduction rate; and (2) the length of the reproductive period. A decrease in the reproduction rate shifts the calcite flux maximum from full moon to new moon. A short reproduction period intensifies the full moon flux maximum, especially at high reproduction rates. The total monthly calcite flux, however, is independent of these variables. An estimate for the carbonate flux in the Red Sea due to G. sacculifer alone is 1 g m-2 year-1. © 1994.