Cyanobacterial mass-occurrences have increased since the end
of the 1970s in the Baltic Sea . The main
bloom-formers are Aphanizomenon flos-aquae and Nodularia
spumigena. Anabaena sp. is also present, but usually at less than
10% of total community. Anabaena can occur as the dominant
cyanobacterium especially in the northern part of the Baltic Sea
. N. spumigena was considered for a long time
as the only toxin-producing cyanobacterium in the Baltic Sea;
however, recently Anabaena sp. has also proven to be toxic
. Since then tens of strains have been isolated,
of which several produce microcystin
. It is, thus, worthwhile to study the ecological
role of toxin production of Baltic Sea Anabaena more thoroughly