Spatial and temporal variation in diversity of pleurocerid gastropoda and other benthic macroinvertebrate fauna, Mukwonago River, Wisconsin

Abstract

Benthic macroinvertebrate taxa were sampled using Hess and coring samplers in two locations of the Mukwonago River in Waukesha County gravel substrates immediately downstream from the Phantom Lake dam, and sand substrates further downstream in Wisconsin State Natural Area #417. The following physical-environmental data were collected simultaneously: water temperature, bottom flow velocity, DO, EC, pH, turbidity and light intensity. Discharge and Gage Height were provided by the USGS for station 05544200. Collection frequency was biweekly below the dam and monthly within the SNA417 from June through November of 2011. Gastropods of the Family Pleuroceridae were the target organisms of the study, although all taxa were collected, sorted, identified to the lowest level possible and counted.

Biotic index and species richness metrics were high, confirming the previous designation of the Mukwonago River as an Exceptional Water Resource. The Pleurocerid gastropod species: Elimia livescens and Pleurocera acuta were particularly abundant at both localities, with E. livescens dominant in gravel substrates and P. acuta dominant in sand substrates. This relationship between the two species held throughout the sampling interval. As most of the other physical-environmental parameters varied little between the two sampling locations, substrate was taken to be the primary determinant of gastropod dominance within the faunas. Further work of the study will include the GIS mapping of the Pleurocerid distributions throughout the state using published records and Milwaukee Public Museum data, and secondary production derived from size-frequency data for both species.