Nodularin analyses and toxicity of a Nodularia spumigena (Nostocales, Cyanobacteria) water-bloom in the western Gulf of Finland, Baltic Sea, in August 1999

During 2–12 August 1999, the development of a surface bloom dominated by the cyanobacterium Nodularia spumigena was followed in the western Gulf of Finland, Baltic Sea. Intense surface scums of aggregated N. spumigena existed on calm days. The low-nutrient N. spumigena-dominated water mass was separated by a front from a nutrient-rich water mass dominated by Aphanizomenon cf. flos-aquae (Nostocales, Cyanobacteria). Owing to inadequate mixing of the two water masses, it is likely that N. spumigena growth was based mainly on the use of internal phosphorus stores. Signs of cell decay were observed on 5 August, and the proportion of empty filaments in the community increased towards the end of the survey period. A high number of Nitzschia spp. (Bacillariophyceae) was recorded within the N. spumigena aggregates on 8 August, suggesting nutrient leakage from the N. spumigena filaments. Senescence of N. spumigena and a decrease in the proportion of intact N. spumigena cells in dry material resulted in de...