Diversity, occurrence, and habitats of the diatom genus Bacteriastrum (Bacillariophyta) in the northern Adriatic Sea, with the description of B. jadranum sp nov.

Ongoing phytoplankton monitoring programs over the last 12 years in the northern Adriatic Sea showed that the diatom genus Bacteriastrum is an important component of the pelagic diatom assemblage. The main goals of this study were to identify which Bacteriastrum species occur in the northern Adriatic Sea and describe their distributions. Bacteriastrum comosum and B. hyalinum f. princeps were rare, while B. delicatulum, B. hyalinum, and B. mediterraneum were frequently present, together with the newly proposed species B. jadranum, described herein. This new species is weakly silicified and is mainly characterized by a large aperture between each cell of the filament. Cells are connected to each other by 8-12 setae, which cross at a distance equivalent to the diameters of 2-3 cells. There is no difference in the orientation of the setae on the two terminal cells, hence the species is placed in the section Isomorpha. The new species was recorded throughout the study area, in both coastal and offshore waters, with higher cell abundances in the vicinity of the Po River during the September-October period. The maximum cell abundance of B. jadranum was 244.2x10(3) cells l(-1) in the surface waters at 44.75666667 degrees N, 12.75 degrees E in September 2006, sometimes representing up to 46% of the entire phytoplankton assemblage, as recorded in the surface waters at 45.06833333 degrees N, 13.515 degrees E in October 2008.