*3.1. Algal Growth in the Mono-Cultures under Normal Growth Conditions*

## 3.1.1. Cell Density and Algal Photosynthetic Efficiency

In the PAR treatment, three species could all persistently grow and reached the maximum cell density on Day 14 (Figure 1). Meanwhile, the maximum cell density of *C. pyrenoidosa* was higher compared to the other two species, and toxic *M. aeruginosa* propagated more slowly. By comparison, the significant inhibitive effects (*p* < 0.05) of UV-B radiation were observed on algal growth, including cell density on a specific day, the maximum cell density during the incubation, and the duration of exponential growth. More specifically, three species both grow slowly and their cell densities began to decrease on Day-10 in the UV-B treatment. For algal photosynthetic efficiency, *Fv/F<sup>m</sup>* of three species in the PAR treatment gradually increased before Day-10 and decreased afterwards. The variation patterns of algal *Fv/F<sup>m</sup>* were different in the UV-B treatment, which decreased from the beginning, increased during Day 2–10, and declined afterwards. Moreover, algal *Fv/F<sup>m</sup>* on a specific day in the UV-B treatment was always lower (*p* < 0.05) than that in the PAR treatment.

For *C. pyrenoidosa* and non-toxic *M. aeruginosa* under normal growth conditions, µmax in the UV-B treatment was significantly lower (*p* < 0.05) compared with those in the PAR treatment (Figure 2), which indicated the negative effects of UV-B on the intrinsic growth potential of two species. Although µmax of toxic *M. aeruginosa* was lower in the PAR treatment compared with the other two species, it did not change significantly (*p* > 0.05) with daily UV-B radiation in our study.
