Native Nontolerant Coolwater Fishes Uniquely Affect Great Plains Streams

Occurrence of Great Plains fishes is constrained by anthropogenic alterations in habitat, climate and biotic interactions.  Potential loss of species of entire functional groups may diminish the provision of goods and services by streams, because fish can affect ecosystem structure and function of North American Great Plains streams. Nineteen experimental stream mesocosms were used to compare the effects of central stoneroller Campostoma anomalum (N=5), white sucker Catostomus commersoni (N=4) and Iowa darter Etheostoma exile (N=5) with a fishless control (N=5). During a 60-day experiment that began on October 11, 2012, ecosystem properties including algal filament length and biomass, invertebrate densities, wholestream metabolism (i.e., NEP, GPP, CR), and nutrient retention were measured in three sampling periods. Algal filament length increased in all streams, except those stocked with central stoneroller.  There were no significant changes in total nitrogen retention, but the average of total phosphorous retention decreased 311% between days 5 and 30, regardless of fish treatments.  Gross primary productivity trends showed an increase during the midpoint of the experiment when water temperatures were warmest (mean 8.51⁰C) and the greatest difference was between the fishless control and the central stoneroller treatment. No trends were detected for these variables during the final sampling period when water temperatures were coldest (mean 2.06⁰C). Our results indicate that single species are capable of uniquely affecting stream properties and further research is warranted for the investigation of potential interaction effects within representative assemblages of Northern Great Plains fishes.