The occurrence of a bloom-forming green alga Pleodorina indica (Volvocales) in the downstream reach of the River Malse (Czech Republic)

In mid-August 2003 a massive bloom of the green alga Pleodorina indica (Iyengar) Nozaki (Volvocales) occurred in the downstream reach of the River Malse in the Czech Republic. An exceptionally long period of the hot dry weather resulted in low flow conditions and warm water temperatures. These environmental conditions combined with high nutrient concentrations led to the macroscopic appearance of P. indica in the form of an extensive surface scum formation with diurnal changes. The alga soon dominated the river phytoplankton, attaining concentrations of 2000 colonies per millilitre. The bloom persisted in the river from the 10-17 August when it was eventually flushed out. P. indica is an indigenous species of tropical climatic regions and prior to this its massive occurrence has not been reported in the temperate region of Central Europe.