2.1. Study sites
The experiment was repeated at two sites, at Tva¨rminne in
the western Gulf of Finland, and Reposaari in the Bothnian Sea
(Fig. 1). The sites differ in salinity, eutrophication level and
cyanobacteria bloom frequency. Tva¨rminne is more saline 5.3–
6.1%, than Reposaari that is almost fresh 1.1–2%, due to the
large influence by River Kokema¨ kijoki. The sites also differ in
level of eutrophication. The Gulf of Finland has a bad status
concerning eutrophication, whereas Bothnian Sea has a poor
status (HELCOM, 2009). Cyanobacteria blooms have increased
significantly in the Gulf of Finland since the end of 1970s