Nodularia spumigena blooms and the occurrence of hepatotoxin in the Gulf of Gdańsk

Nodularia spumigena forms extensive summer blooms in the Baltic Sea. The occurrence of the blooms is determined by water temperature, light intensity and nutrient concentration; levels of nitrogen and phosphorus in particular are critical. The time of the seasonal maximum and intensity of the Nodularia bloom in the Gulf of Gdańsk vary significantly from year to year. In 2001 a rapid and massive proliferation of N. spumigena was observed in late June – early July. The concentration of nodularin in water ranged from 90 to 18 135 μg dm−3 and in lyophilised phytoplankton samples from 3000 to 3520 μg g−1 d.w. (dry weight). Such a high concentration of toxin in the recreational waters of the Gulf of Gdańsk constitutes a health risk for users of bathing areas. In 2002, the N. spumigena bloom was less dense, but lasted longer, with a maximum in late July – early August. In 2002 the concentration of nodularin did not exceed 12.6 μg dm−3 in water and 919 μg g−1 d.w. in lyophilised phytoplankton samples. Other cyanobacterial toxins – microcystins and anatoxin-a – were also detected in the coastal waters of the Gulf of Gdańsk.