Water-blooming and toxin-producing cyanobacteria in Swedish fresh and brackish waters, 1981-1995

During the period 1981-1995 331 phytoplankton samples from 153 stations in different parts of Sweden were analysed regarding species composition and possible toxicity. Toxins were indicated in 156 samples which gives a percentage of 47. The toxicity was confirmed by mouse bioassay. All samples were collected from water-blooming lakes, mainly containing taxa belonging to the cyanobacterial genera Anabaena, Aphanizomenon, Microcystis and Planktothrix. In addition to information about occurrence of neuro- or hepatotoxins, knowledge about the distribution of water-blooming lakes in the country was obtained as well as about their predominating taxa. Microcystis aeruginosa, Anabaena flos-aquae and Aphanizomenon flos-aquae were the most frequently occurring taxa in the lakes. Among the taxa observed, nine different cyanobacterial species with certainty produce toxins. Microcystis spp. most frequently produced toxic blooms (only hepatotoxins). Anabaena spp., however, caused the majority of waterblooms. The Anabaena flos-aquae-group produced neurotoxins [incl. anatoxin-a(s)], neurotoxins + hepatotoxins or only hepatotoxins. Aphanizomenon flos-aquae was only recorded as toxin-producing in three Swedish lakes, which may be compared with the conditions in Finland, where it was toxic in 36 bloom samples. Aspects are given on toxicity versus lake acidification and trophic conditions, as well as on health effects on animals and human beings.