Effects of fathead minnows and restoration on prairie wetland ecosystems

Abstract

SUMMARY 1. Research has shown that fish influence the structure and processes of aquatic ecosystems, but replicated studies at the ecosystem level are rare as are those involving wetlands. Some wetlands of the Prairie Pothole Region (PPR) of North America support fish communities dominated by fathead minnows (Pimephales promelas) while others are fishless, providing an opportunity to assess the influence of these fish on wetland ecosystems. Additionally, many wetlands have previously been drained and subsequently restored, but the success of these efforts is poorly known and restoration may be impeded by the presence of fish.2. We assessed the effects of fathead minnows and drainage by studying 20 semipermanent, prairie wetlands in Minnesota from 1996 to 1999. We used a 2 × 2 factorial design to examine the effects of presence and absence of minnows and drainage history (restored/never drained) on the abundance of aquatic invertebrates and amphibians, as well as on the concentrations of chlorophyll a, total phosphorus, total nitrogen and turbidity in the water column.3. Results showed that fathead minnows are an important determinant of many biotic and abiotic characteristics of wetlands in the eastern PPR. Wetlands with fathead minnows had fewer aquatic insects, large‐ and small‐bodied cladocerans, calanoid copepods, ostracods and larval tiger salamanders, as well as a higher abundance of corixids and greater turbidity and chlorophyll a. A higher concentration of phosphorus in restored basins was the only consistent effect of past management.4. Fathead minnows usually dominate fish communities in eastern PPR wetlands where fish are present, and can have several strong ecosystem effects. While abiotic variables are important determinants of ecosystem structure in prairie wetlands, they can be strongly influenced by biotic factors.