Aquatic invasive species are among the greatest threats to freshwater biodiversity. The aim of this study was to understand the effects of two invasive watermilfoil species (Myriophyllum heterophyllum Michx. and Myriophyllum spicatum L.) on native macrophyte communities and to assess community response to a range of invasion intensities as well as examine the influence of canopy types. We hypothesized that some communities would be more sensitive to invasion, and that some canopy species would facilitate watermilfoil presence. We used a novel approach to give better representation of the 3D aspect of the community which involved employing a modified quadrat approach to sample at two Connecticut lakes. Results show that watermilfoil invasion has a significant negative effect on native species richness. Floating canopy does not vary with invasion intensity, but submerged canopy does. One species, (Utricularia purpurea Walter), was associated with high native species richness and rarely occurred with invasive species. The results identify potential species that are disproportionally threatened by invasive species, as well as identifying invasion indicator species. The examination of canopy effects is uncommon in aquatic invasion ecology, and this study suggests that this aspect may have significant effects on resilience to invasion and overall community dynamics.
The authors would like to thank the resident communities surrounding the lakes for their tolerance during the field season. They would also like to thank the White Memorial Conservation Center and the Connecticut Agricultural Experiment Station for advice and assistance identifying specimens. We would also like to thank the UK Natural Environment Research Council for their support to FCK (program Oceans 2025–WP 4.5 and grants NE/D521522/1 and NE/J023094/1). This work also received support from the Marine Alliance for Science and Technology for Scotland pooling initiative. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions.
- Myriophyllum spicatum
- Myriophyllum heterophyllum
- invasive species