Date of Award

Summer 2019

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)


Biological, Environmental, and Earth Sciences

Committee Chair

Kevin Kuehn

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Halvor Halvorson

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Jake Schaefer

Committee Member 3 School

Biological, Environmental, and Earth Sciences


In lotic freshwater systems, aquatic macroinvertebrates are key processors of biofilms that grow upon organic matter. Although macroinvertebrate effects on biofilms may depend on light availability, the combined effects of consumers and light remain unexplored. Here, I conducted experiments to test effects of presence/absence of the omnivorous shrimp Macrobrachium ohione and the shredding caddisfly Pycnopsyche sp. on Liriodendron tulipifera litter biofilms in experimental streams under light or darkness. I measured litter-associated algal, fungal and bacterial biomasses and production rates, as well as litter decomposition, over 49 days. Both experiments exhibited significant positive effects of light on algal productivity and interactions of Macrobrachium and Pycnopsyche presence with time and light. Light increased bacterial productivity in the Pycnopsyche experiment, but not in the Macrobrachium experiment, in which time, light, and Macrobrachium interactively affected bacterial production. Litter decomposition was unaffected by light or Macrobrachium presence, but Pycnopsyche presence increased decomposition rates. My results suggest that light strongly affects litter biofilms, whereas consumers primarily affect the timing and succession of periphytic microbial colonization of organic matter. Compared to omnivores, shredder-detritivores may exert stronger effects on turnover and decomposition of organic material within lotic systems.