Recurrent depth maxima of the hepatotoxic cyanobacterium Oscillatoria agardhii

Toxic cyanobacteria, which have been implicated in human illness and animal mortalities, are common in many lakes, but their seasonal and vertical distribution is poorly known. We report persistent and recurrent metalimnetic blooms of Oscillatoria agardhii in the eutrophic Lake Östra Kyrksundet (southwest Finland) and associated toxin peaks analyzed quantitatively using liquid chromatography. Marked metalimnetic maxima of toxic O. agardhii developed during 1988–90. The desmethyl-microcystin-RR (a cyclic heptapeptide hepatotoxin) levels in the metalimnion were 20–40 μg∙L−1 and paralleled the chlorophyll a concentrations.