Although temporary stages are common in dinoflagellates, their role remains unclear. Every year, A. taylori forms dense patches (10⁶ cells/L) in La Fosca beach (Spain, NW Mediterranean), lasting for 2 months (July, August). One of the characteristics of the life history of A. taylori is the formation of temporary cysts. The hypothesis of the temporary cysts accumulated in the sediment play an important role in the sudden population increases observed once the adverse environmental conditioned have past is explored. Temporal changes in the abundances of temporary cysts in the sediment and, the in situ encystment and excystment dynamics of temporary cysts are presented. The daily in situ flux of the temporary cysts from water column to the sediment in the maintenance period of the bloom is of the order of 10⁴ cysts/m2/day, whereas the flux of the daily excystment is 10³ cysts/m2/day. Part of the temporary cysts in the sediment take more than one day to produce vegetative cells and remain viable in the sediment at least 4 days as a possible short-term population reserve. The data is analysed in view of the proposed hypothesis.