Diatom community structure along physico-chemical gradients in Southern Caspian Sea (Noor shore)

Diatom species diversity and cell abundance are influenced by environmental factors. The effect of physicochemical factors on interseasonal dynamics of planktonic diatom community structure was examined along Noor shore of Caspian Sea to determine which of the variables impact more on the diatom diversity, distribution and cell number. Overall, 144 samples were collected during four sampling campaigns along four transects of 2 km long each with three sampling sites in 2014 (February, May, July and November). In total, 62 diatom species were identified, of which 27 species were typical marine or brackishwater and the rest were marinefreshwater or freshwater. In the present study, diatom species diversity was highest in winter. As a result, ShannonWiener Index was 3.5 in winter, while in spring it was reduced to 0.8. Among the revealed species, the centric Thalassiosira caspica was the most abundant (up to 2.75 ×10^6 cells L^-1). Comparison of species and their abundances between coastal, middle and offshore stations, as well as all stations as a whole, showed that they differed (Test X 2, p 0.05) except for Navicula sp. (in summer) and Ulnaria ulna (in autumn and winter). Canonical correspondence analysis results showed that in particular temperature and salinity, in the second place transparency, phosphates and to a lesser extent dissolved oxygen and pH can affect diatom species diversity and abundance. Diatoms Thalassiosira fasciculata, T. caspica and Melosira caspica may be recommended as biological indicators along the shore of Caspian Sea.