Date Approved


Graduate Degree Type


Degree Name

Biology (M.S.)

Degree Program


First Advisor

Dr. Carl R. Ruetz III

Second Advisor

Dr. Eric Snyder

Third Advisor

Dr. Steven Kohler

Academic Year



Fish can have strong top-down effects on their prey through both direct predation and non-consumptive effects in streams. We conducted manipulative field experiments to test the strength of fish predation on benthic macroinvertebrates at the patch scale in Stegman Creek. Stegman Creek is a small (0.39 m3/s at baseflow), groundwater-fed stream in western Michigan with abundant mottled sculpin (Cottus bairdii) and brown trout (Salmo trutta) acting as benthic predators. We hypothesized that fish predation decreases macroinvertebrate density, thereby increasing periphyton biomass through a reduction in density of grazing macroinvertebrates. We placed paired predator-exclusion cages and open-control cages in a 250-m stream reach (n=12 pairs) during summer 2015 and winter 2016. Cages for the summer and winter trial were in the stream for 32 and 31 days, respectively. Overall, we found evidence that macroinvertebrate densities were lower in the presence of predators (i.e., open-control cages) than in their absence (i.e., predator-exclusion cages), which was consistent with top-down control by fish on macroinvertebrates. We found evidence of an indirect effect of fish on periphyton during summer but not winter. Our results suggest that mottled sculpin and brown trout are acting as benthic predators in Stegman Creek and display top-down control on macroinvertebrates, in the summer months as well as in winter months.

Available for download on Tuesday, August 26, 2025