Changes in Structure of Zooplankton Communities in the Middle Daugava (Western Dvina) Over the Last Five Decades

Zooplankton communities of the Daugava River were investigated in two river stretches: the river stretch from Surozha in Belarus to Dunava in Latvia in 2008 and the Kraslava–Dunava stretch in 2005–2009. Samples of zooplankton were collected at the right and left banks as well as in the middle of the river. The comparison of the results obtained with findings of the studies performed in similar sections of the Daugava River in 1956–1966 shows that the total number of zooplankton taxa in 2005–2009 has decreased by 48 taxa. Relevant changes have been recorded in the structure of taxa. The observed tendency for the total amount of zooplankton and species diversity to decrease is probably due to the changing hydrological situation in the Daugava drainage basin and long-term climate changes.