Oral Presentation Society for Freshwater Science 2026 Annual Meeting

Investigating optimal detection strategies for and ecological impacts of invasive European Frog-bit (Hydrocharis morsus-ranae) in Michigan inland lakes (135605)

Joshua Tellier 1
  1. Michigan Department of Environment, Great Lakes, and Energy, Lansing, MICHIGAN, United States

European Frog-bit (H. morsus-ranae), or EFB, is an aquatic invasive plant in North America primarily found in sheltered, shallow water. First found in Michigan in 1996, it remained primarily along Great Lake coastlines. Despite being a prohibited species in the state, rapid spread to inland lakes began occurring in 2016. Several populations are now known to exist in inland lakes throughout the state. Where present, EFB can form dense mats, smothering native vegetation and substantially altering habitat in important nursery areas for aquatic animals. Recognizing the potential for EFB to impact Michigan’s abundant freshwater resources, the Michigan Department of Environment, Great Lakes, and Energy (EGLE) set out to identify optimal detection strategies for EFB and to characterize the ecological impacts of this invader. Beginning in 2022, and in collaboration with several other agencies and university groups, Michigan EGLE piloted a study comparing detection frequency and the aquatic plant communities of lakes known to contain EFB against those known to be free of EFB. Twenty lakes (ten containing EFB, ten without) of similar relative size, habitat characteristics, and trophic state were sampled using multiple methods (e.g., point-intercept, targeted shoreline meander) to identify the most efficient method for detecting EFB, balancing detection probability with field staff effort. During the two-year sampling period, eighty-seven other aquatic plant species were identified across the twenty study lakes. This robust dataset allowed EGLE to compare aquatic plant communities in lakes with and without EFB to inform management decisions and invasion response. Several statistical methods were used to investigate whether EFB alters the littoral plant community, most notably cluster analysis applied to dissimilarity matrices among lakes. Lakes naturally clustered into groups of similar composition, but EFB did not appear to be a determining factor for any cluster in-group.