Koraljka Kralj

PSEUDO-NITZSCHIA BLOOMS IN THE ZRMANJA RIVER ESTUARY (EASTERN ADRIATIC SEA)

The spatial and temporal distribution of the diatom genus Pseudo-nitzschia was investigated in the small, highly stratified Zrmanja River estuary (eastern Adriatic Sea) from 1998 to 2004. During this period, Pseudo-nitzschia spp. mostly dominated the phytoplankton assemblages (abundance close to 1.3 × 106 cells L−1, appeared in 51% of the samples). The maximum abundance of Pseudo-nitzschia spp. was during mid-winter (February 1999), when it contributed up to 85% of the total diatom abundance. Pseudo-nitzschia bloom was significantly correlated with phosphorous concentration and temperature, whereas there was no significant correlation with total inorganic nitrogen, silicate and salinity. The very broad range of environmental factors over which Pseudo-nitzschia spp. were observed suggests there was more than one Pseudo-nitzschia species in the diatom assemblage. Morphological analysis has shown that the dominating Pseudo-nitzschia species corresponded to Pseudo-nitzschia calliantha. Two other species were encountered; one identified as Pseudo-nitzschia heimii, while other has yet to be identified. This study was the first to find P. heimii in the Adriatic Sea and the first to record the presence of a potentially toxic diatom P. calliantha in an Adriatic estuary.

The relationship between phytoplankton species dominance and environmental variables in a shallow lake (Lake Vrana, Croatia)

The shallow Lake Vrana was studied over a 1-year period, special attention being paid to the phytoplankton. Phytoplankton was investigated monthly with respect to temporal variability of selected environmental factors. The regular annual development observed was in species contribution to total biomass rather than in seasonal changes in species composition. The assemblage was dominated by Cosmarium tenue Arch. and Synedra sp. In winter and in spring the phytoplankton assemblage was dominated by Cosmarium tenue and high contribution of Synedra sp. was observed during the summer and autumn. Results suggest that concentrations of inorganic nitrogen and phosphorus were critical in regulating phytoplankton biomass and species dominance.

Observations on the diatom Navicula hedinii Hustedt (Bacillariophyceae) and its transfer to a new genus Envekadea Van de Vijver et al. gen. nov.

The population of an unknown naviculoid diatom from Lake Vrana in Croatia was identified as Navicula hedinii, a species described in 1922 from a small lake in eastern Turkestan (China). This species has some similarities with Navicula pseudocrassirostris, a marine species found in European coastal waters. Based on the ultrastructure of the two species, they can no longer be included within the taxonomical concept of Navicula sensu stricto. Following a comparative morphological analysis of both species with genera bearing similar characters (Adlafia, Veigaludwigia, Kobayasiella, Cavinula, Stenoneis, Climaconeis, Berkeleya, Sellaphora, Cosmioneis), a new genus, Envekadea is proposed for the two species. The new genus is characterized by a sigmoid raphe course with golfclub-like terminal fissures deflected in opposite directions, the areolae covered by external porous hymenes and the presence of one chloroplast, H-shaped in valve view.