Morphology and germination pattern of the resting cyst of Peridiniella catenata (Dinophyceae) from the Baltic Sea

The resting cyst of the cold-water dinoflagellate Peridiniella catenata is described from sediments collected off the southwest coast of Finland, Balt ic Sea. The timing of germination was determined for this cyst type, and th e dynamics of benthic cysts and planktonic cells were investigated during t he seasonal cycle. The discoid, colourless, and thin-walled cysts germinate d after a dormancy period of six months, and the emerging vegetative cells were identified as P. catenata. Synchronized excystment occurred in midwint er at 2 degrees C. The decrease of cyst abundance in the surface sediments coincided with the appearance of vegetative cells in the water column. The decay of the vegetative population was followed by a massive input of cysts into the sediments. It is concluded that cyst formation, dormancy interval , and the timing of germination play a role in regulating the seasonal appe arance of P. catenata in the water column.