Effects of Ca2+ on encystment and growth in Scrippsiella trochoidea

Cysts serve as a seed source for the initiation and recurrence of a harmful algal bloom (HAB) caused by dinoflagellates. And the influence of calcium on cyst formation has been relatively understudied. In the present study, we investigated the effects of calcium (Ca2+) on the growth and encystment of Scrippsiella trochoidea. We incubated S. trochoidea in modified f/2 media in flasks which were divided into five groups and treated with different Ca2+ concentrations (0, 0.2, 0.4, 0.6, and 0.8 g·L−1). We revealed that cell density increased with increasing Ca2+ concentrations; however, cell density was reduced when Ca2+ concentrations exceeded 0.2 g·mL−1. Additionally, the number of cysts and the cyst formation rate similarly increased as Ca2+ concentrations increased, but these were reduced when Ca2+ concentrations exceeded 0.4 g·mL−1. Lastly, S. trochoidea absorbed Ca2+ from the water when cysts were formed and under high Ca2+ concentrations, more calcareous thorn cysts formed.