Supplementary Materials

Figure S1. Laboratory set up used to assess effects of exclusion cage size on water velocity. Adjustable acrylic boxes that mimicked field exclusion cages were placed within an experimental flume with velocity 6 cm s-1. Baskets of rocks were placed inside the acrylic boxes to mimic our field experiment setup (see S2). A microscale thermal anemometer was inserted into holes in the lid of acrylic boxes perpendicular to the flow of water. Velocity was measured in 2 mm increments starting at the substrate surface.

Figure S2. Exclusion cages deployed in a 2nd order stream. Half of the exclusion cages were screened with 1 mm mesh to exclude macroinvertebrates and fish. Substrate was removed from the area so that the bottoms of exclusion cages were level with the stream substrate. Baskets of autoclaved rocks were placed within exclusion cages to facilitate algae and macroinvertebrate collections.

Figure S3. Experimental setup of exclusion cages deployed in a 2nd order stream. Baskets of autoclaved rocks were placed within exclusion cages to facilitate algae and macroinvertebrate collections. Exclusion cages varied in size and materials used. Half of the exclusion cages were screened with 1 mm mesh to exclude macroinvertebrates and fish. Screened and unscreened exclusion cage types were grouped together in sets of four, with each set having a random assignment of cage types.

Figure S4. Proportional abundance of algal functional groups in screened exclusion cages (n=20), unscreened exclusion cages (n=20), and outside of exclusion cages (n=10). Chain forming pennate diatoms were not included in graphs because they comprised <1% of all samples. SinPen=Single pennate diatoms, ChainCent=Chain-forming centric diatoms, FilCy=Filamentous cyanobacteria, CocCy=Coccoid cyanobacteria, FilGr=Filamentous green algae, ColGr=Colonial green algae, SinGr=Single green algae.

Figure S5. Proportional abundance of algal functional groups in small acrylic (Acr; n=10), small polypropylene (Sm PP; n=10), medium polypropylene (Med PP; n=10), and large polypropylene (Lg PP; n=10) exclusion cages. Chain forming pennate diatoms were not included in graphs because they comprised <1% of all samples. SinPen=Single pennate diatoms, ChainCent=Chain-forming centric diatoms, FilCy=Filamentous cyanobacteria, CocCy=Coccoid cyanobacteria, FilGr=Filamentous green algae, ColGr=Colonial green algae, SinGr=Single green algae.

Figure S6. Macroinvertebrate community structure in screened (n=20) and unscreened (n=20) exclusion cages. Organisms occurring in less than three baskets (<0.075% of total individuals) were combined in the “Other” category, which included Hydroptilidae, Scirtidae, Perlodidae, Tipulidae, Hydrophilidae, and Entomobryidae. Chi=Chironomidae, Sim=Simuliidae, Eph=Ephemerellidae, Bae=Baetidae, Iso=Isonychiidae, Hept=Heptageniidae, Perl=Perlidae, Nem=Nemouridae, Phi=Philopatomidae, Hyd=Hydropsychidae, Oli=Oligochaeta.

Figure S7. Macroinvertebrate community structure in small acrylic (Acr; n=10), and small (Sm PP; n=10, medium (Med PP; n=10), and large polypropylene (Lg PP; n=10) exclusion cages. Organisms occurring in less than three baskets (<0.075% of total individuals) were combined in the “Other” category, which included Hydroptilidae, Scirtidae, Perlodidae, Tipulidae, Hydrophilidae, and Entomobryidae. Chi=Chironomidae, Sim=Simuliidae, Eph=Ephemerellidae, Bae=Baetidae, Iso=Isonychiidae, Hept=Heptageniidae, Perl=Perlidae, Nem=Nemouridae, Phi=Philopatomidae, Hyd=Hydropsychidae, Oli=Oligochaeta.

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