engleski

Morphology, phylogeny and diversity of the diatom genus Pseudo-nitzschia in the northern Adriatic Sea

The diatom genus Pseudo-nitzschia contains more than 30 chain forming species. Most of them are discernible only on the basis of ultrastructural or genetic differences. Ultrastructural investigations, combined with genetic characterization with different molecular markers have revealed several cryptic and pseudo-cryptic species within the genus Pseudo-nitzschia. This ubiquitous genus is present in phytoplankton assemblages of the northern Adriatic Sea throughout the entire year and is often found to be dominating the diatom community. However, the actual species composition and species succession is, due to the limitations of light microscopical determination, still unknown and requires further examination. Samplings were performed over a one year period in coastal and offshore waters of the northern Adriatic Sea. Pseudo-nitzschia spp. were the dominant diatoms, present in 60 % of all samples on a yearly basis, with a maximum contribution up to 97 % (1.6 x 106 cells L-1) of the total diatom abundance. Morphological analyses revealed P. manii and the potentially toxic P. pseudodelicatissima, P. pungens, P. fraudulenta and P. calliantha as the dominant species in different blooms over the year. In order to further elucidate phylogeny and diversity of Pseudo-nitzschia species clonal cultures were established. Subsequent phylogenetic analysis based on sequences of 18 S rDNA and morphological analysis of the frustules revealed P. calliantha, P. frudelenta, P. pseudodelicatissima and P. pungens. This research adds to the scarce knowledge of species of this genus in the northern Adriatic Sea.

phytoplankton; taxonomy; Pseudo-nitzschia; northern Adriatic

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