The effects of fluid flow on the spatial density, distribution, and metabolism of larval Glossosoma

Abstract

The focus of this research was the mechanistic relationship between fluid flow, spatial density, distribution, and metabolism of stream-dwelling insect larvae of the caddisfly genus Glossosoma (Glossosomatidae: Trichoptera). Glossosoma are ecologically important for many reasons, including that they are dominant grazers in lotic food webs, are capable of suppressing stream periphyton, and act as an indicator of stream health. A description is herein presented of fluid flow and stream bathymetry environments where Glossosoma are often present. Predictive relationships for Glossosoma spatial density are proposed from local fluid flow and channel bathymetry variables. The research was conducted through a series of four separate studies. First, habitat was quantified for larval Glossosoma in three coastal mountain streams in northern California. Applying dimensional analysis, a functional relationship was developed for predicting larval abundance. Variogram analysis of Glossosoma spatial density and bed topography revealed overlap in the separation distance above which point measurements were statistically independent. Second, field measurements were conducted in Valley Creek, Minnesota and data were compared with the measurements in the coastal mountain streams. Third, a computational model was employed to estimate high resolution fluid flow variables along a riffle in Valley Creek. Simulation results were verified and implemented in a predictive model for Glossosoma abundance. Fourth, a laboratory study of Glossosoma metabolism under varying flow conditions revealed generally increasing oxygen consumption with increasing fluid flow velocities. The proposed research will be instrumental for predicting not only how Glossosoma respond to changes in fluid flow and stream bathymetry conditions, but also how these variables influence larval spatial density, distribution, and behavior in lotic environments.