Prvi nalaz proizvodnje domoične kiseline u kulturama vrste Pseudo-nitzschia calliantha iz srednjeg Jadrana

In this study, three isolates of the potentially toxic diatom genus Pseudo-nitzschia were analysed for morphological and toxicological features. Cultures of Pseudo-nitzschia were established from seawater samples collected from the southern part of the Velebit Channel (central Adriatic Sea) during February 2019. All culture isolates were identified by scanning electron microscopy (SEM) as Pseudo-nitzschia calliantha. Domoic acid (DA) production was confirmed in all isolates analysed. The highest concentrations of cellular DA were found in early culture stages, with the lowest cell abundance, for all P. calliantha isolates. This study is the first to report DA production by P.calliantha isolated from the Adriatic Sea.Ovim istraživanjem analizirane su morfološke i toksikološke osobine potencijalno toksičnog roda dijatomeja Pseudo-nitzschia. Tri stanične kulture Pseudo-nitzschia uspostavljene su iz uzoraka morske vode prikupljenih iz južnog dijela Velebitskog kanala (srednji Jadran) tijekom veljače 2019. Pretražnim elektronskim mikroskopom (SEM) utvrđeno je da sve izolirane kulture pripadaju vrsti Pseudo-nitzschia calliantha. Proizvodnja domoične kiseline (DA) potvrđena je za sve analizirane izolate. Najviše koncentracije stanične DA u svim izolatima vrste P. calliantha određene su u ranoj uzgojnoj fazi, s najmanjom brojnošću stanica. Ovo istraživanje je prva potvrda proizvodnje DA u kulturama vrste P. calliantha izoliranim iz Jadranskog mora

High proliferation of Pseudo-nitzschia cf. arenysensis in the Adriatic Sea: ecological and morphological characterisation

The aim of the present study isto characterise the diatom Pseudo-nitzschia community during a bloom period together with environmental conditions. High proliferation of Pseudo-nitzschia spp. was observed in September 2017 at the shellfish breeding area in the Krka River estuary (Central eastern Adriatic Sea). The peak of abundance (1.8 x 106 cells L-1) was recorded at 7 m depth, and the increased abundance persisted for four weeks.Morphological analyses of field samples based on scanning electron microscopy (SEM) revealed that Pseudo-nitzschia cf. arenysensis was prevailing (94%) in the Pseudo-nitzschia assemblage. Several strains were successfully isolated from net samples in order to better define morphological features and phylogenetic characterisation. The isolated Pseudo-nitzschia strains corresponded morphologically to the P. cf. arenysensis from the field samples, based on our SEM observations. Phylogenetic analysis demonstrated that the Croatian strains grouped with P. arenysensis using the ITS and LSU rDNA sequences. Spearman rank correlation showed that salinity was an important environmental factor affecting the vertical distribution of Pseudo-nitzschia spp. in this highly variable area. Availability of increased concentration of orthophosphates and ammonium and low Si: TIN ratio may have promoted the bloom of P. cf. arenysensis in the estuary

Phytoplankton Dynamics in the Middle Adriatic Estuary, with a Focus on the Potentially Toxic Genus Pseudo-nitzschia

The Krka River estuary is a karstic, permanently stratified estuary due to the strong freshwater inflow. It is a special environment in which to study the phytoplankton community, especially because this area is an important aquaculture site. Among other potentially toxic phytoplankton species, the diatom genus Pseudo-nitzschia occurs frequently and is a potential source of domoic acid (DA), causing shellfish toxicity and human intoxication. The main objective was to examine the dynamics of the phytoplankton community and, in particular, the genus Pseudo-nitzschia in the upper part of the Krka estuary, through monthly sampling over two years. The phytoplankton community was analysed using light microscopy and scanning electron microscopy to determine the diversity of Pseudo-nitzschia species and characterise the environmental parameters associated with a high abundance of Pseudo-nitzschia species. Seven Pseudo-nitzschia species were identified in the investigation, with higher frequencies and abundances in the less variable layer, at a 7 m depth. Blooms of Pseudo-nitzschia were noted in the late summer/early autumn, dominated by P. delicatissima/arenysensis. Winter assemblages were characterised by P. pseudodelicatissima/cuspidata, P. calliantha, and P. subfraudulenta, and were associated with domoic acid occurrence in shellfish