Effects of the invasive species Elodea nuttallii on native macrophyte communities: : Evidence from coastal brackish bays in the northern Bothnian Bay

Sammanfattning

Invasive species are widely recognized as one of the main drivers of global diversity loss, a severe ecological impact. Elodea nuttallii (E. nuttallii) is a particularly problematic one and in Sweden it is considered the most invasive aquatic plant. The purpose of this study was to examine how E. nuttallii affects native plant communities in an area not extensively studied before, the northern Bothnian Bay. By gaining a better understanding of its influence in this area a solid baseline could be provided for understanding E. nuttallii in this part of the world and for assessing whether it behaved similarly to populations elsewhere. A field study in four bays in the Piteå archipelago was conducted to examine biomass-dominance, frequency, species diversity and evenness in areas dominated by E. nuttallii (Elodea areas) and in areas with mixed, native vegetation (Mixed areas). Elodea nuttallii proved to influence its surroundings, but perhaps not as clearly as observed elsewhere in the world. Elodea areas did generally not exhibit higher biomass than Mixed areas, despite the species’ capacity to form dense mats. Furthermore, species diversity and evenness was only significantly higher in the Mixed area compared to the Elodea area in one bay. However, E. nuttallii was more biomass-dominant than the plant category “Other” (all other plants combined) in most Elodea areas. Although not always dominant, E. nuttallii was present in nearly all samples, suggesting it is highly prevalent. Due to the invasive plant’s spatial variability in dominance and diversity, the results suggest that E. nuttallii is likely regulated by local conditions rather than following a uniform invasive behavior, potentially giving the northern Bothnian Bay a slight advantage in managing or delaying the spread of E. nuttallii.