Invasive reed effects on benthic community structure in Lake Erie coastal marshes

We examined how dominance (% canopy cover) and invasion date of the common reed, Phragmites australis, affected benthic macroinvertebrate diversity and density in 8 wetlands along Lake Erie’s southern shoreline. We also compared macroinvertebrate densities among patches of reed, cattail (Typha spp.), and native flora and epiphyton communities on submerged stems of reed and cattail. Narrow-leaf cattail (T. angustifolia) is also a common invasive to these wetlands, but is generally considered more desirable than reed because it has not caused major changes in plant community composition, or supposedly altered wetland function. Macroinvertebrate diversity (Shannon-Weaver H’) was positively related to reed cover and was highest (4.6) in a marsh where reed invaded ~30 years ago and comprises ~99% of the hydrophyte community. Shading by dense stands of reed increased H’-diversity, in part, by reducing the abundance of duckweed, which harbored large numbers of a few species of surface-inhabiting amphipods. Average macroinvertebrate density was significantly greater in Phragmites and native flora than in Typha, and diatom-dominated epiphyton was consistently denser on reed and native flora than on cattail across wetlands. Our findings suggest that Phragmites does not necessarily detrimentally affect macroinvertebrate community structure and diversity and that invasion history alone has little affect on the H’-diversity-reed dominance relationship in these marshes.