The rise and fall of a toxigenic population of Microcystis aeruginosa (Cyanophyceae/Cyanobacteria)—a decade of observations in Lake Akersvatnet, Norway

Abstract

The phytoplankton community of Lake Akersvatnet before 1968 was dominated by Planktothrix mougeotii (Bory ex Gomont) Anagnostidis et Komárek (= Oscillatoria agardhii Gomont var. isothrix Skuja). Non-filamentous species of cyanophytes, however, became subsequently frequent. Populations of Microcystis aeruginosa (Kützing) Lemmermann exhibited regular mass development during the period 1968–1989. In summer 1984 the presence of microcystin-LR was detected during a nuisance bloom. Toxic blooms of M. aeruginosa were a recurrent phenomenon until 1989. The population of Microcystis was then suppressed, and microcystin was present in trace concentrations only or could not be detected. The phytoplankton was subsequently dominated by species of Anabaena and Aphanizomenon and in 1994 by the dinoflagellateCeratium hirundinella (O.F. Müller) Dujardin, Our results suggest an interrelation between changes in cyanophyte bloom composition and toxin production during various stages of eutrophication.