Influence of substrate size, Cladophora , and caddisfly pupal cases on colonization of macroinvertebrates in Sagehen Creek, California

Colonization of stream macroinvertebrates onto artificial substrates was examined in Sagehen Creek, California, during 1993. Substrate size and presence or absence of pupal cases of the caddisfly Anagapetus (Glossosomatidae) were examined as possible influences on macroinvertebrate colonization. Macroinvertebrates were collected from substrates after 60 d of incubation and identified to the lowest feasible taxonomic unit. Dry weight of the filamentous green alga Cladophora also was determined for each substrate. A general linear model indicated a significant positive relationship between both substrate size and presence of pupal cases on richness ( P Anagapetus cases on Micrasema bactro , Epeorus , and Rhyacophila sp. 1, and of substrate size on Hydropsyche occidentalis and Epeorus . Neither cases nor substrate size had a significant effect on Cladophora density ( P > 0.05). There were significant negative correlations between Cladophora density and both Shannon H′ and J′ indices. There were significant positive relationships between Cladophora density with Baetis , Simulium , and Chironomidae density. Combined main effects of substrate size, Anagapetus pupal cases, and Cladophora have dynamic influences on this macroinvertebrate fauna. This study demonstrates the complex interplay of biotic and abiotic factors that determine macroinvertebrate distribution and abundance in this system.