Effect of pH on the morphology and viability of Scrippsiella trochoidea cysts in the hypoxic zone of a eutrophied area

•This study is the first report of an experimental investigation of the morphological changes of cysts of S. trochoidea.•The cause of morphological changes of S. trochoidea cysts was identified from the results in the acidification experiment.•The calcareous spines of S. trochoidea cysts play an important role in their survival.

To investigate the cause of morphological change of Scrippsiella trochoidea cysts and its ecological significance in the hypoxic zone of a eutrophied area, the effect of pH on the morphology and viability of S. trochoidea cysts was studied. In the acidification experiment, the dissolution of calcareous spines of S. trochoidea cysts was observed at less than pH 7.39, indicating that the morphological change of S. trochoidea cysts is caused by the low pH levels in acidic sediments of hypoxic zone. After being exposed to intense acidic environments, cysts of S. trochoidea without calcareous spines were able to germinate; however, they seem to be easily linked to degradation in the sediments. These results suggest that the survival of S. trochoidea cysts is being threatened by environmental conditions in the hypoxic zone of eutrophied area.