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Planktonic diatom species of the genus Pseudo-nitzschia are common in oceanic and neritic plankton worldwide. Fourteen Pseudo-nitzschia species have been known as producers of domoic acid, a neurotoxic amino acid responsible for Amnesic Shellfish Poisoning (ASP), therefore considerable scientific interest on its ecology and taxonomy has been generated. During the last two years several field investigations have been conducted in the Telašćica aquatorium, two in 2011 (May and October) and four in 2012 (February, March, May, and August). Pseudo-nitzschia pseudodelicatissima "sensu lato" was one of the dominant diatom species in May of 2011 (maximal abundance of 1.5 x 104 cells L-1, contributed up to 11% of the total diatom abundance) and August of 2012 (maximal abundance of 1.1 x 104 cells L-1, contributed up to 95% of the total diatom abundance). Pseudo-nitzschia seriata appears in October of 2011 (maximal abundance of 0.4 x 104 cells L-1, contributed up to 0.3% of the total diatom abundance). Monoclonal cultures of Pseudo-nitzschia cells (isolated from May and August samples) were established and molecular analysis on different molecular markers (18S, ITS1-5, 8S-ITS2, 28S) has been performed. Phylogenetic analysis resulted in the identification of P. mannii and potentially toxic P. fraudulenta. Statistical phylogenetic networks demonstrate genetically unique populations for both species in the middle Adriatic. The genus was present throughout the year and dominated the community in summer and early autumn, urging continuous monitoring of the system. The difficulty in monitoring these diatoms is in classification to the species level. This relies on ultra-structural features seen only on cleaned frustules observed with an electron microscope or by molecular methods. Furthermore, studies elucidating the nutrient and physical requirements, as well as the biotic interactions of Pseudo-nitzschia species and species composition on regional and global scales are essential for the prediction and prevention of its mass occurrence and resulting toxicity. |
