Abstract: Scrippsiella trochoidea is a worldwide algal bloom dinoflagellate. Temporary cysts are the immobile cells, which formed by vegetative cells to withstand transient adverse environmental conditions. The temporary cyst of S. trochoidea plays an important role in the life cycle and occurrence of algal blooms. Effects of darkness on the formation, survival and germination of temporary cystsofS. trochoidea were examined under three temperatures (8, 20 and 25 ℃) in this study. Results showed that formation of temporary cysts started at the first day after darkness treatment, with the highest cyst formation rate occurring at day 3 to day 5. In addition, the peak of cyst formation delayed at higher temperatures. The final accumulative cyst formation rates were 15.9%, 20.1%, and 9.9% at 8, 20, and 25 ℃, respectively. Temporary cysts could not survive for a long time, whose death occurred just after one day of formation. All cysts died after 8-16 days of storage at darkness. The survival time was longer at low temperature, with the half-lethal time being 5.9, 2.9 and 2.7 days at 8, 20 and 25 ℃, respectively. There was no mandatory resting period for temporary cysts, with germination occurring within 24 hours after incubation. The maximum accumulative germination rates of 43.3%-65.6% were obtained at 3-6 days. The germination rate was higher for cysts formed at low temperature. Our results indicated that S. trochoidea was easy to form temporary cysts, which germinated rapidly under suitable conditions. This study highlighted the importance of temporary cysts in the population dynamics and bloom occurrence and collapse of S. trochoidea.

Key words: thermal discharge, zooplankton, β diversity, environmental factor, generalised dissimilarity modelling (GDM).