Influence of macrophyte abundance on population dynamics of slimy sculpin (cottus cognatus) and related food web structure in cold-water streams in western Wisconsin

Abstract

Slimy sculpin (Coitus cognatus) are important inhabits of cold-water streams in southwestern Wisconsin. Unpublished data suggests that small-bodied sculpin are more abundant in stream riffles with high macrophyte cover than those where macrophytes are scarce. The objectives were to determine if the presence of abundant macrophytes affects the density of different size classes of sculpin and those differences were driven by the influence of macrophyte presence oflocal food web structure. Basal carbon sources, macroinvertebrate prey, and slimy sculpin were sampled during the fall in the Coon Creek watershed of Wisconsin, and food webs were constructed using stable isotope analysis. Data were compared between sites with high and low macrophyte abundance. Periphyton biomass and the density and bioinass of common macroinvertebrate families were similar between areas of high and low macrophyte abundance. Slimy sculpin were not segregated by size between these site types, however the total density of slimy sculpin was significantly higher in areas with high macrophyte abundance. Macrophyte abundance influences sculpin distribution by providing refuge from predators and providing greater prey availability. The food webs at sites with abm1dant and scarce macrophyte cover were detritus based. In the fall, aquatic and terrestrial based detritus are important carbon sources in areas with high-macrophyte growth.