Role of temporary cysts in the population dynamics of Alexandrium taylori (Dinophyceae)

Although temporary cyst stages are common in dinoflagellates, their role remains unclear. Every year Alexandrium taylori (Dinophyceae) forms dense patches (106 cells l−1) along La Fosca beach (Spain, northwest Mediterranean), which last for 2 months (July, August). One of the characteristics of the life history of A. taylori is the shift from a vegetative motile stage to non-motile temporary cysts. Here we present the temporal changes in the abundance of temporary cysts in sediments and their in situ encystment and excystment rates. The in situ encystment rate of temporary cysts from the water column to the sediment ranged from 1.8 × 106 to 4.4 × 106 cysts m−2 day−1, whereas the excystment rate was between 0.9 × 106 to 2.7 × 106 cysts m−2 day−1 during the bloom period. Some of the temporary cysts in the sediment took more than 1 day to produce vegetative cells and remained viable for at least 4 days. We propose that temporary cyst formation in this species is a tool for reducing population losses. The production of temporary cysts can be an advantage since part of the population is stored in the sediments.