Occurrence of cyanobacterial blooms in the baltic sea in relation to environmental conditions

Abstract

Abstract Cyanobacterial blooms occur regularly in summer in central parts of the Baltic Sea. They are mainly composed of Aphanizomenon sp. and Nodularia spumigena . Both species have almost similar ecological requirements and can roughly be considered a uniform functional group. In order to identify factors that might favour bloom development, water quality data from monitoring programmes were compared with bloom distribution. A salinity from 3.8 to 11.5 PSU proved important for the spatial distribution of the bloom development. The bloom's onset was triggered by temperatures approximating 16°C provided that global radiation was > 120 W/m 2 (daily mean) and wind speed was < 6 m/s. Nutrient concentrations decreased immediately before the bloom. The bloom's development ceased with poor weather conditions characterized by low irradiation or high wind speed.