Current distribution, trends, abiotic and biotic preferences of two Elodea species in Bulgaria

Two invasive aquatic macrophyte species from the genus Elodea and their distribution in Bulgaria were studied. The research was based on 653 field surveys from the period 2009-2022. Elodea records constitute to only 6% of the database. Between the two species studied, E. nuttallii exhibited a wider distribution both in rivers and lakes (natural and artificial). Several instances of invaders’ dominance were observed, with E. nuttallii showing dominance patterns mainly in lakes, and E. canadensis in rivers. Both species were distributed in aquatic habitats with a wide variation in abiotic characteristics, except for the dominant substrate. E. nuttallii showed a more significant altitudinal range reaching above 1500 m. Such altitudinal variations resulted in diverse ecological habitats in terms of abiotic factors such as temperature and light intensity. The studied aquatic macrophyte communities demonstrated average species richness. Ceratophyllum demersum and Myriophyllum spicatum were the most commonly recorded representatives of the native aquatic flora. Canadian waterweed demonstrated the ability to form dense communities in rivers, while Nuttall’s waterweed retained average values of abundance. A case of natural disappearance within the Elodea species has been documented. The systematised information covering a 13-year period could serve to identify strategic areas for monitoring aquatic IAS and their management