Predicting the potential distribution of neophytes in Southern Germany using native Najas marina as invasion risk indicator

Twenty-four aquatic neophytes have been introduced to Germany so far and at least 16 non-native species established stable populations in northern and north-western Germany. Invasive aquatic neophytes can cause serious ecological and economic problems in lakes and other freshwater ecosystems. In the presented study, a species distribution model was used to identify possible habitats for neophytes in Bavaria (Southern Germany) and to predict which Bavarian lakes might become suitable habitats for neophytes due to climate change. A total of 55 Bavarian lakes were fitted with high-resolution temperature loggers as part of this monitoring programme. Furthermore, the physical and chemical properties of the lakes were determined and verified in regular intervals. The presence or absence of the native thermophilic macrophyte Najas marina L. was used as an indicator to determine whether a lake was a suitable habitat for neophytes. The results revealed that the spread of neophytes in Bavaria is mainly limited by spring and summer water temperature. In contrast, nutrient concentrations in the water showed no significant influence. Suitable lakes reached temperatures of at least 15 °C for 2 months during spring and at least 20 °C for 2 months during summer. By comparison, the water temperatures in lakes classified as not suitable for neophytes were 2–5 °C lower. The computed predictions for the estimated temperature increase of 1.4 °C, for the period between 2021 and 2050, indicate that up to 70 % of Bavarian lakes might become suitable habitats for neophytes.