Many lakes in North America have been invaded by Eurasian watermilfoil, Myriophyllum spicatum, and there is an increasing pressure to manage this invasion to improve recreational lake use and restore native macrophytes. However, there are very few studies on the effects of invasive macrophyte eradication on the rest of the community. Feeding interactions are particularly sensitive to changes in underwater habitat, most of which is structured by macrophytes. This study was designed to determine whether fish feeding was 1) affected by large-scale changes in plant composition after selective control of Eurasian watermilfoil and 2) correlated with habitat complexity or abundance of invasive plants on a smaller scale. Popnets were used to simultaneously collect plant, invertebrate, and fish data in the littoral zone of four Minnesota lakes twice a year for 4 years. We examined stomach fullness and niche width as a function of invasive plant abundance and habitat complexity and conducted a multivariate analysis of bluegill, Lepomis macrochirus, feeding selectivity in the context of changing plant communities.
Results/Conclusions
Degree of stomach fullness did not correlate with the proportion of invasive plants or habitat complexity. Bluegill exhibited high selectivity for Diptera and their preferences varied little in different plant habitats, despite differences in macroinvertebrate communities. There were changes in bluegill niche width in different years but they were not consistent with invasive plant control. Overall, selective Eurasian watermilfoil eradication with timely restoration of the native plant community did not affect characteristics of fish feeding under investigation. This study also contributes to our understanding of fish-macroinvertebrate interactions as a function of habitat complexity in large temperate lakes.
