engleski

Searching for aliens - update on Egeria densa Planchon and Myriophyllum heterophyllum Michx. in the Neretva River Delta (Southern Dalmatia)

The Neretva River Delta represents the largest complex of wetland habitats in the Croatian coastal zone. In addition to being a Ramsar site, the Delta is protected on the national level as one of a few preserved wetland areas in the Mediterranean region of Europe. The area is nowadays greatly transformed into agricultural land, with most water bodies well interconnected, as a result of numerous anthropogenic interventions since the 19th century onward. First records of alien aquatic plants Egeria densa and Myriophyllum heterophyllum in the Delta occured in 2013 and 2016, respectively. Prior to our survey, E. densa was recorded on five sites, while M. heterophyllum was recorded on one site in the delta. For the purpose of detailed mapping of these taxa, we carried out a survey of the Neretva River Delta in August 2018. Our search has revealed a greater abundance than previously recorded, indicating the recent spread of the two taxa. Egeria densa was rather frequent, recorded in over 12 sites, often forming dense monodominant populations, with the largest one recorded in the Norin River, a right bank tributary of the Neretva River, extending almost continuously for approximately 7 km from the Prud Spring to the settlement Romići. Myriophyllum heterophyllum was recorded in eight sites, however morphologically dubious specimens of Myriophyllum were found in additional 20 sites, possibly hybrids between alien M. heterophyllum and native M. verticillatum. Both M. heterophyllum and E. densa were recorded in bloom, with the latter developing only male flowers. Interestingly, E. densa was frequently found in springs, with water temperature below 20 °C.

alien plants ; aquatic invasions ; hybrid ; mapping ; new records

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