Plant architecture and epiphytic macroinvertebrate communities: the role of an exotic dissected macrophyte

The abundance of epiphytic macroinvertebrates on aquatic macrophytes can be influenced by different plant architecture types. For example, dissected plants can provide epiphytic macroinvertebrates more substrate for foraging and more cover from predators than undissected plants. Large changes in macrophyte community composition have the potential to strongly influence whole lake macroinvertebrate abundance if overall plant architecture changes. For example, when the exotic macrophyte Eurasian watermilfoil (Myriophyllum spicatum L., EWM), a dissected plant, invades a lake and becomes dominant, fundamental changes in lake-wide plant architecture occur. We conducted a 6-lake field study and a meta-analysis to examine whether macroinvertebrate density and biomass varies predictably with plant architecture and, if so, whether these relationships are evident at the whole-lake scale when EWM dominates the plant community. We found that higher macroinvertebrate densities and biomass per g of plant were associated with dissected plants than undissected plants in both our field study and our meta-analysis of published studies. However, in our field study, macroinvertebrate densities and biomass per g of plant decreased as the % of EWM cover increased across lakes, although not always significantly. This result suggests that EWM provides different habitat for macroinvertebrates than native dissected plants. Therefore, the macrophyte community may support lower densities and biomass of macroinvertebrates when EWM is dominant at the whole-lake scale. Reduced abundance of macroinvertebrates could have strong impacts on other components of lake food webs.