Effects of Macrophyte Bed Architecture on Largemouth Bass Foraging: Implications of Exotic Macrophyte Invasions

Abstract

Invasive, canopy-forming macrophyte species such as Eurasian watermilfoil Myriophyllum spicatum and hydrilla Hydrilla verticillata are now widespread throughout North American lakes and reservoirs. However, their effects on economically and ecologically important species such as largemouth bass Micropterus salmoides are insufficiently understood. Canopy-forming exotic macrophytes typically displace structurally diverse native macrophytes. In aquaria, we tested whether exotic macrophyte canopies negatively affect age-0 largemouth bass foraging success compared with diverse macrophyte assemblages. In addition, we explored the relative effects of macrophyte density, and prey density of bluegills Lepomis macrochirus on largemouth bass foraging success. Bluegill prey density did not significantly affect largemouth bass foraging success. However, largemouth bass experienced shorter search times and greater attack and consumption rates in moderate plant density treatments (compared with dense) and diverse plant treatments (compared with canopy monocultures). Effects of macrophyte density and architecture (diverse versus canopy monoculture) on largemouth bass foraging success were similar in magnitude. Our results indicate that among lakes, the relative importance of macrophyte density and architecture to largemouth bass foraging will depend upon the extent to which each factor influences structural complexity.