Habitat effects on invertebrate drift in a small trout stream: implications for prey availability to drift-feeding fish

Abstract

In this study, we focused on the drivers of micro-and mesohabitat variation of drift in a small trout stream with the goal of understanding the factors that influence the abundance of prey for drift-feeding fish. We hypothesized that there would be a positive relationship between velocity and drift abundance (biomass concentration, mg/m 3 ) across multiple spatial scales, and compared seasonal variation in abundance of drifting terrestrial and aquatic invertebrates in habitats that represent the fundamental constituents of stream channels (pools, glides, runs, and riffles). We also examined how drift abundance varied spatially within the water column. We found no relationship between drift concentration and velocity at the microhabitat scale within individual pools or riffles, suggesting that turbulence and short distances between high-and low-velocity microhabitats minimize changes in drift concentration through settlement in slower velocity microhabitats. There were also minimal differences in summer low-flow drift abundance at the mesohabitat scale, although drift concentration was highest in riffle habitats. Similarly, there was no differentiation of drifting invertebrate community structure among summer samples collected from pools, glides, runs, and riffles. Drift concentration was significantly higher in winter than in summer, and variation in drift within individual mesohabitat types (e.g., pools or riffles) was lower during winter high flows. As expected, summer surface samples also had a significantly higher proportion of terrestrial invertebrates and higher overall biomass than samples collected from within the water column. Our results suggest that turbulence and the short length of different habitat types in small streams tend to homogenize drift concentration, and that spatial variation in drift concentrations may be affected as much by fish predation as by entrainment rates from the benthos.

Spatial and temporal patterns of macroinvertebrates in drift and on substrate of a mountain stream (Cordoba, Central Argentina)

“…Therefore, we agree with Waters (1965) who points out that the drift structure at a given stream point depends not only on local production but also on upstream distant areas. In other studies conducted in small and medium order streams of the northern hemisphere, the highest drift densities were observed in riffles (Leung et al, 2009;Rader, 1997).…”

“…This is consistent with the fact that the drift integrates populations from different communities of a river section (Waters, 1965;1972;Hynes, 1970). Several authors studied seasonal variation of the structural attributes of the stream's macroinvertebrate communities in temperate climates (Gualdoni et al, 1991;Shearer et al, 2002;Leung et al, 2009) by Insecta and the most abundant orders were Ephemeroptera, Trichoptera and Diptera. The same insect taxa showed high densities in drift and benthic community in neotropical streams (Ramírez and Pringle, 1998b;.…”

“…results also showed a clear segregation of the run and riffle benthic assemblages. Few research studies have considered changes in the drift among fluvial habitats of mountain streams (Leung et al, 2009). In the drift of Achiras stream, diversity and evenness did not differ between riffle and run.…”

“…The study of drift process has increased in recent decades because of the importance of this phenomenon in the fish feeding ecology Leung et al, 2009); in the effect of pesticides (Gladsø and Raddum, 2002;Jergentz et al, 2004 a, b) and in the interpretation of landscape changes as a consequence of human actions (Svendsen et al, 2004).…”

“…Traditionally, the drift phenomenon has been studied on a limited spatial scale such as one river (Svendsen et al, 2004) or at stream reach level. However, research on changes in composition and structure between fluvial habitats and the factors contributing to this variation is scarce (Leung et al 2009;Boyero and Bosch, 2002;Brooks et al, 2005). Drift studies conducted in Córdoba province (Argentina) have shown that, in a braided river reach, mayflies, chironomids and oligochaetes were the dominant groups with a distinct seasonal variation (Gualdoni et al, 1991;Corigliano et al, 2001).…”