Modelling the distribution of a submerged invasive macrophyte and its potential biological control agent in invaded ranges

Understanding current and potential geographical distributions of invasive species is an important part of natural resource management. Therefore, the aim of this study was to evaluate the current and future climate suitability of Lagarosiphon major, an invasive aquatic weed, and assess establishment potential for Hydrellia lagarosiphon, its candidate biological control agent. Using MaxEnt species distribution models, we identified climatically suitable regions for L. major invasion under current and projected climates. Additionally, mechanistic modelling was employed to map potential establishment zones for H. lagarosiphon, in order to determine overlap. Our findings indicate that more than 90% of New Zealand is currently suitable for L. major, with climate change expected to have minimal impact. In contrast, Australia and Europe exhibit limited suitability (8% and 15%, respectively), with future projections showing reduced suitability and a northward shift in Europe. Additionally, no climatic overlap was found between South Africa and invaded ranges. This highlights the adaptability of L. major to diverse environmental conditions. For H. lagarosiphon, degree-day modelling predicts viable populations across most invaded regions in New Zealand, supporting its potential as a biological control agent. This could help mitigate the impact of L. major in invaded sites, provided adaptive strategies are implemented.