Cylindrospermopsin (CYN) is a cytotoxic alkaloid produced by cyanobacteria. The distribution of this toxin is expanding around the world and the number of cyanobacteria species producing this toxin is also increasing. CYN was detected for the first time in Turkey during the summer months of 2013. The responsible species were identified as Dolichospermum (Anabaena) mendotae and Chrysosporum (Aphanizomenon) ovalisporum. The D. mendotae increased in May, however, C. ovalisporum formed a prolonged bloom in August. CYN concentrations were measured by LC-MS/MS and ranged from 0.12 µg·mg−1to 4.92 µg·mg−1 as dry weight, respectively. Both species were the only cyanobacteria actively growing and CYN production was attributed solely to these species. Despite CYN production by C. ovalisporum being a well-known phenomenon, to our knowledge, this is the first report of CYN found in D. mendotae bloom.

This study evaluated the phytoplankton communities based on functional groups to obtain information about the water quality of Lake İznik, Turkey. The phytoplankton consisted of 103 taxa, classified in 12 phytoplankton functional groups (PFGs), with dominancy of 5 species, Chrysosporum ovalisporum, Dolichospermum mendotae, Planktothrix rubescens, Fragilaria capucina, and Mougeotia sp. The Shannon-Wiener diversity index (H') was calculated and results ranged between 0.41 and 2.47. The redundancy analysis (RDA) and Spearman's correlation analysis were used to assess the relationships between the PFGs and environmental variables. According to the multiple comparisons of the data, the main efficient factors that determined the seasonal distribution of the PFGs were TP, DO, SiO 2 , SD, and pH. The ecological requirements of the dominant PFGs (