Garden Ponds: Hidden Sources for Plant Invasions?

Private garden ponds are increasingly popular among homeowners and can, to some extent, compensate for the loss of natural habitats, but they may be sources of invasive species as pond owners often introduce alien ornamental species. We assessed the popularity, distribution and sources of six invasive macrophyte taxa ( Elodea spp., Eichhornia crassipes , Ludwigia spp., Myriophyllum aquaticum , Pistia stratiotes and Vallisneria spp.) in garden ponds across Hungary using a citizen science approach. Using Species Distribution Modelling (SDM), we predicted the potential spread of these taxa into natural waters, comparing the results to confirmed occurrences in the wild. Based on 560 responses, we found that even banned invasive macrophytes remain highly popular and widespread. Pond owners purchase them from various sources, including garden centres, web stores and online communities, with the latter being especially difficult to monitor and regulate. In the European Union, regulations already prohibit the import, possession, and trade of listed invasive species, and customs authorities are responsible for checks at the point of entry. Nevertheless, our findings indicate that invasive species remain widely available, highlighting the complementary need for extensive educational campaigns and outreach activities.