Spreading of Dreissena rostriformis bugensis (Andrusov, 1897) in the Danube River (Serbia)

Detailed limnological investigations of the Serbian Danube stretch at 11 sampling sites in a 396 km long sector of the Danube River (from 1260 r-km to 863.4 r-km) were performed from April 2002 to November 2010. Samples were collected seasonally (April, June, September and November). A Ponto-Caspian element, quagga mussel Dreissena rostriformis bugensis (Andrusov 1897), was found for the first time in the Serbian Danube stretch in April 2010 at sampling site Veliko Gradiste (1059 r-km). Our furthest upstream finding of this species was at site Ram (1071 r-km). Species identification was done by the morphology of its shells. In addition, a comparison with another dreissenid species Dreissena polymorpha (Pallas 1771) was made based on shell morphology. Population density of quagga mussel was low, with the ratio of D. polymorpha to D. rostriformis bugensis being around 5:1. The finding of D. rostriformis bugensis in the Serbian Danube stretch is evidence that this invasive Ponto-Caspian species moved the limit of its distribution upstream in the Danube River which is one of the main corridors used for its spread from Eastern (Romania, Bulgaria) to Western Europe.Ministry of Science and Technological Development of the Republic of Serbia [146021]; Serbian Ministry of Education and Science [176018