"Natural" Variability of Macrophyte Communities in Glacial Lakes: Results from Repeated Whole-Lake Hydroacoustic and Species Surveys

A range of disturbances at different scales affect macrophyte communities and thus the fish communities that use these habitats.  Lake/Fisheries managers must understand underlying system variability to judge whether change in macrophyte growth in a managed lake is due to the macrophyte management action or natural variability.  Past research demonstrates that interannual variability in macrophyte abundance depends on lake productivity.  Eutrophic lakes typically exhibit higher variability than mesotrophic lakes regardless of whether aquatic plants are being managed.  I present results from multi-year point-intercept and hydroacoustic aquatic plant surveys on an unmanaged, native-only eutrophic Minnesota Lake and eutrophic Wisconsin Lake infested with Eurasian watermilfoil.  Results demonstrate large changes in vegetation biovolume and invasive species dominance from year to year with no aquatic plant management.  Consequently, monitoring reference conditions should complement any fisheries habitat study or program where macrophytes are being manipulated.