Blooms of the potentially toxic diatom Pseudo-nitzschia calliantha Lundholm, Moestrup & Hasle in coastal waters of the northern Adriatic Sea (Croatia)

The genus Pseudo-nitzschia contains more than 30 species, though most of them are discernible only on the basis of ultrastructural or genetic differences. We present a taxonomic study of Pseudo-nitzschia calliantha Lundhum, Hasle & Moestrup in the coastal waters of the northern Adriatic Sea together with domoic acid (DA) measurements on natural and breeding populations of shellfish. Sampling carried out monthly at 13 stations during 2007 showed Pseudo-nitzschia species to be present with high abundances during the entire year, forming blooms in coastal waters (reaching abundances of up to 1.2 × 106 cells L−1) during the late summer/early autumn, when they contributed up to 70% of the whole phytoplankton community. Ultrastructural examination provided evidence that the observed blooms were formed by the potentially toxic species P. calliantha. After the P. calliantha bloom, DA was detected at 3 stations along the north-eastern Adriatic coast with concentrations ranging from 0.11 to 1.32 μg g−1 in shellfish tissue. The distribution patterns of the species were analyzed statistically in order to explain the relationships between environmental variables and population dynamics. We here report on a mass appearance of the potentially toxic P. calliantha in the coastal waters of the northern Adriatic.

► Ecology and distribution of a toxic algae bloom in the northern Adriatic.
► A mass appearance of toxic diatom P. calliantha was observed in the northern Adriatic.
► Co-occurring domoic acid accumulation in natural shellfish populations.