The contemporary records of aquatic plants invasion through the Danubian floodplain corridor in Serbia.
Aquatic ecosystems are particularly vulnerable to introductions of non-indigenous species, which potentially lead to major disruptions in the functioning of these invaluable habitats. Despite the significance of aquatic systems, there is no collated data available on the aquatic non-native plants in Serbia. Consequently, the aim of this paper is to provide a first overview of the aquatic alien plant species recorded in Serbia, their origins, current distribution, habitat preferences and invasiveness status. This study comprises the results of a comprehensive literature review and extensive field research on lake and river systems over a nine year period (2007-2015), with the addition of data from the IASV database and Joint Danube Surveys 2 & 3. The results of this study show the presence of seven non-indigenous aquatic plant species in Serbia which, despite being a relatively low number when compared to France and Germany, is in line with most of the countries of the region (e.g. Croatia, Bulgaria and FYR Macedonia). The majority of the species are native to the Americas, which concurs with the results of previous studies at the European level, with only one species of Asian origin. The most abundant of the registered non-natives is Vallisneria spiralis, followed by Azolla filiculoides and Elodea nuttallii, while Cabomba caroliniana, as the newest registered aquatic alien in Serbia, has the least number of records. All of the registered non-natives predominantly occur in running waters, including as much as 91% of the records for Elodea canadensis and 85% for Elodea nuttalli. Vallisneria spiralis is present in five different EUNIS habitat types, while Paspalum distichum was recorded predominantly along the River Danube, thereby highlighting it as P. distichum's main corridor of spread in Serbia. The distribution of all the recorded non-indigenous species is primarily linked to the northern, low-lying part of Serbia - i.e. Vojvodina Province. Such a distribution pattern is concordant with the presence of adequate habitat types, the courses of potential international invasion corridors in the Sava and Danube rivers and the position of the elaborate irrigation canal network of the Danube-Tisa-Danube Hydrosystem; but also with the frequency of studies carried out in this region over the years. Of the seven aquatic aliens present in Serbian waterbodies, three are considered to be highly invasive and one potentially invasive, while two have also been included in the list of 150 most widespread alien species in Europe.