Modelling the risks of invasive aquatic species spread in Swedish lakes

Species distribution modelling is a valuable tool for identifying areas most at risk of the spread of invasive species. Here we model the environmental factors governing the distributions of two invasive species of concern that are currently found in Sweden at only a limited number of locations: the aquatic macrophyte Elodea nuttallii (Nuttall’s waterweed / smal vattenpest) and the bivalve Dreissena polymorpha (Zebra mussel / vandrarmussla). For E.nuttallii, the greatest risk factors are connectivity with other water bodies (facilitating dispersion), human population density and length of growing season. This implies that it is principally well-connected lakes in populated areas of southern Sweden that are most at risk of further spread (although other areas of concern are identified). For D.polymorpha, water alkalinity and the proportion of agricultural land (a source of nutrient pollution) are the most important factors, and the models identify lakes Vänern and Vättern, waters in parts of Östergötland, Jämtland and Gotland as key areas of concern for further spread.