Bacillariophyta made up the highest number (37 genera,

87 species), but with a remarkably low abundance (8.1%), followed by Pyrrophyta (15 genera, 31 species). Chlorophyta, Cyanophyta and Euglenophyta were represented by 18, 10 and 10 species, respectively. Silicoflagellates was represented by only one species. On the other hand, Euglenophyta was the first group quantitatively (86.8%). Many species (38) were rare, having a frequency of occurrence of about 1.85%, but they were very important because they controlled the levels of species diversity. The total number of species on the sampled stations demonstrated more pronounced variations at the spatial scale than the temporal one. A high diversity (100 species) was recorded at station 1, followed by 66 GSK1120212 in vitro species at station 2, and approximately similar numbers of species (57–59 species) were recorded at stations 3, 5 and 9, while a conspicuously smaller numbers (47–52 species) were found at stations 4, 6, 7, 8, 10 and 11. The numbers of phytoplankton species recorded in winter, spring, summer, autumn 2012 and winter 2013 were 51, 44, 59, 72 and 74 respectively. In spite of the large number of species, only ten were perennial: Chaetoceros affinis Lauder, 1864, Cyclotella kützingiana Thwaites, Leptocylindrus danicus Cleve, 1889, Skeletonema costatum (Greville) Cleve,

1873, Exuviaella marina Cienkowski, 1881, Oxytoxum sceptrum (Stein) Schroder, 1906, Prorocentrum micans Ehrenberg, 1834, Prorocentrum triestinum J. Schiller, see more 1918, Scrippsiella trochoidea

(Stein) Balech ex Loeblich III, 1965 and Chlorella marina Butcher R. W., 1952. The most representative genera were: Skeletonema, Glutathione peroxidase Asterionellopsis, Cyclotella, Pseudo-nitzschia and Leptocylindrus from diatoms, Prorocentrum, Exuviaella and Gyrodinium from Pyrrophyta, and Protoperidinium from heterotrophic dinoflagellate. The most dominant genus of Euglenophyta was Eutreptiella. The most dominant in frequency were the diatom, Skeletonema costatum and the Pyrrophyta Exuviaella marina (86% and 83% occurrence, respectively), Prorocentrum micans, Prorocentrum triestinum, Scrippsiella trochoidea and Cyclotella kützingiana appeared in more than 50% of the samples. Chlorophytes and cyanophytes did not contribute greatly to the abundance of total phytoplankton and had average annual 4863 and 178 cells l−1, respectively. In Shannon Wiener legislation, the lowest and highest species diversities were 0.02 (St.6, spring) and 3.03 (St. 1, winter, 2013). Generally, lowest phytoplankton diversity was observed in spring (0.404 ± 0.45) whereas higher values were recorded in winter 2013 (2.076 ± 0.384). The correlation between phytoplankton density and diversity was strongly negative (r = −0.478, p < 0.001), and it is apparent that minimum diversity means that a stress increases with poor water quality, whereas the opposite is true for maximum diversity results with favourable condition.