Effectiveness of a plastic mesh substrate cover for reducing the effects of common carp on aquatic ecosystems

A great deal of effort has been directed at eliminating or controlling common carp Cyprinus carpio populations, but these efforts have had limited success. We assessed the effectiveness of an alternative approach, using plastic-mesh substrate covers, to reduce environmental effects of common carp, Multiple trophic levels were monitored in 0.06-ha enclosures in experimental ponds that contained either common carp with mesh covers, common carp with no mesh covers, no common carp with mesh covers, or neither fish nor mesh covers. Macroinvertebrates and macrophytes were also sampled over a 1-year period in six field sites with paired mesh cover and control plots. Common carp significantly increased turbidity (NTU) and total phosphorus (μg/L), decreased macrophyte cover (%), altered the relative abundance of zooplankton taxa (N/L), and suppressed macroinvertebrate abundance (N/m²) in ponds. In contrast, carp did not significantly affect either total nitrogen (μg/L) or phytoplankton (μg/L) concentrations. Mesh substrate covers did not significantly reduce any effects of common carp in the pond enclosures. Abundances of macroinvertebrates and macrophytes also did not differ between field plots with and without mesh covers. The lack of effective reduction of common carp-induced effects limits the usefulness of mesh substrate covers as a tool for habitat restoration.