*3.5. Algal Growth in the Mono-Cultures under Nutrient Enrichment Conditions* 3.5.1. Cell Density and Algal Photosynthetic Efficiency

Compared to normal growth conditions, three species all grew steadily under nutrient enrichment conditions and their cell densities did not decrease at the later stage (Figure 7). For *C. pyrenoidosa* and non-toxic *M. aeruginosa*, their cell densities on a specific day and the maximum cell density in the UV-B treatment were significantly lower (*p* < 0.05) than those in the PAR treatment. However, no significant difference in the cell density of toxic *M. aeruginosa* (*p* > 0.05) was observed between PAR and UV-B treatments during the whole incubation process. *Fv/F<sup>m</sup>* of three species gradually increased and decreased afterwards in both PAR and UV-B treatments. Although algal *Fv/F<sup>m</sup>* in the UV-B treatment were lower (*p* < 0.05) than that in the PAR treatment before Day 6, the difference became smaller at the later stage of incubation. For example, *Fv/F<sup>m</sup>* of non-toxic and toxic *M. aeruginosa* were both comparable (*p* > 0.05) in the UV-B and PAR treatments on Day 10 and Day 14.

As expected, µmax of three species increased with nutrient enrichment compared with those under normal growth conditions in the PAR and UV-B treatments (Figure 2). µmax of non-toxic and toxic- *M. aeruginosa* were lower compared with *C. pyrenoidosa*, but they were both comparable between PAR and UV-B treatments (*p* > 0.05).
