Composition of small Thalassiosirales under highly diluted conditions in a eutrophic lake

Abstract

Dominant algae have been changed from cyanobacteria to diatoms since 2000, as a consequence of the massive discharge of Tone River water, and the dominant diatom has been reported as Skeletonema potamos and small Thalassiosirales, although the species of the latter have not been identified. In this study, the dominant species of the small Thalassiosirales in the Lake Tega water from spring (April) to autumn (November) in 2017 were identified in detail by scanning electron microscopy (SEM). The results indicated that small Thalassiosirales were mainly composed of five genera, such as Cyclostephanos, Cyclotella, Discostella, Stephanodiscus, and Thalassiosira. The seasonal trend showed that the most abundant species in April, May, June, and November were Stephanodiscus binderanus, Cyclotella atomus, Discostella pseudostelligera, and C. atomus, respectively. Although Cyclotella meneghiniana occupied a small portion in April, it highly increased and became dominant from July to October.