Impact of Lemna minuta on biodiversity
Lemna minuta (Lemnoideae) is a small free-floating plant species no more than 3 mm in length. It is native to the Americas and is a widespread non-native species in the EPPO region. The species grows in slow moving freshwater, including streams, canals, lakes and drainage ditches. Surveys were conducted in 17 paired aquatic sites in central Italy in 2017 and 2018. Each paired site consisted of one site with more than 80 % surface coverage of L. minuta and one site from which the species was absent. The paired sites were less than 2 km apart and both belonged to the same hydrographic network. At each paired site, sampling of the water chemical properties and the aquatic plant and invertebrate community was conducted. Overall, sites with L. minuta had lower levels of dissolved oxygen, and dissolved oxygen was negatively correlated with the coverage of L. minuta and the thickness of the mats. Light penetration into the water was also reduced compared to sites without L. minuta. As a result, plant species richness was lower in the sites with L. minuta compared to sites without L. minuta. The composition of the aquatic invertebrate community also showed differences. Invertebrate groups which are tolerant of low oxygen levels (Ostracoda, Copepoda and Isopoda) were found in more abundance under mats of L. minuta whereas groups which are less tolerant (Ephemeroptera, Amphipoda, Chironomus and Notonecta) were rare or absent. Due to its small size, the habitats it invades, and its high dispersal capacity, the control of L. minuta is a major challenge. Full removal of the species is difficult, and it is likely that the waterbody could be reinvaded even if removal is achieved. However, removal of the species over the season can help to prevent mat forming and reduce the impact of the species.
Sources
Ceschin S, Ferrante G, Mariani F, Traversetti L, Ellwood NTW (2020) Habitat change and alteration of plant and invertebrate communities in waterbodies dominated by the invasive alien macrophyte Lemna minuta Kunth. Biological Invasions 22, 1325-1337.