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Dominant Pseudo-Nitzschia (Bacillariophyta) species in the Black Sea (Ukraine)

Abstract Terenko L., Terenko G., 2012: Dominant Pseudo-nitzschia (Bacillariophyta) species in the Black Sea (Ukraine) [Vyraujančios Pseudo-nitzschia (Bacillariophyta) rūšys Juodojoje jūroje (Ukraina)]. - Bot. Lith., 18(1): 27-34. Diatoms of the genus Pseudo-nitzschia (order Pennales) are persistent component of the phytoplankton community in the Black Sea and may reach bloom level during some periods in summer and autumn. Six potentially toxic and non-toxic Pseudo-nitzschia species were recorded up to date in the Ukrainian waters. Since 1980s, several mass developments of Pseudo-nitzschia spp. have been observed. Morphological analysis revealed Pseudo-nitzschia delicatissima, P. pseudodelicatissima, P. pungens, P. seriata as the dominant species in the blooms. Pronounced bloom of Pseudo-nitzschia spp. reaching up to 80 % of total phytoplankton abundance and occupying wide area of the Black Sea was observed in June 2001. The summer density peak of P. delicatissima and P. seriata was observed at 16.0-17.5 °С and salinity 15.2-15.7 ‰ in the coastal waters of Odessa Bay. In December 2005, the density of Pseudo-nitzschia spp. in the bottom layers in Odessa region reached 3.0·106 cells l-1. In June 2008, a single species P. pseudodelicatissima bloomed in the Danube region. The density of the species came up to 12.0·106 cells l-1. At the end of May 2009, P. delicatissima showed short-term and lower magnitude density peak (3.1·106 cells l-1) in the coastal zone of Odessa Bay. Thus, the Pseudo-nitzschia spp. blooms are frequent phenomena in the Black Sea and may occur in any season of a year. These species are indicators of trophic state in marine waters.