Abstract
High‐biomass blooms of A. taylori Balech have recently been spreading over new Mediterranean areas, with evident adverse effects on the marine ecosystem. In 1999–2000, a new Mediterranean locality was affected by blooms of A. taylori: the West Bay of Vulcano (Aeolian Islands, Tyrrhenian Sea), with maximum cell densities of 1.2 × 10 7 cells 1 −1 in August 1999 and 4.0 × 10 6 cells 1 −1 in August 2000 observed together with yellowish water discoloration. The seawater samples contained high concentrations of nutrients as DIN (Dissolved Inorganic Nitrogen), especially NH 3 ‐N with values of 14.4 μM and TOT‐P (Total Phosphorus) with values of 3.2 μM due to the anthropic presence and discharge of untreated sewage. The climatic conditions also seem to influence the occurrence and spreading of the A. taylori blooms in the Vulcano Bay. Clonal cultures of A. taylori , established from Italian and Spanish seawater samples, were used for the sequence analyses of the 5.8S rDNA gene and ITS regions in order to study the genetic variability of different geographical populations of Alexandrium species in the Mediterranean area and to further develop the molecular markers for HAB key‐species.