Abstract
The process of macroinvertebrate drift in streams is characterized by dislodgement, drift distance and subsequent return to the bottom. While dislodgement is well studied, the fate of drifting organisms is poorly understood, especially concerning Trichoptera. Therefore, the aim of the present study was to determine the ability of six case-building Trichoptera species to return to the stream bottom under different flow velocity conditions in a laboratory flume. The selected species occur in North-West European sandy lowland streams along a gradient from lentic to lotic environments. We determined species specific probability curves for both living and dead (control) specimens to return to the bottom from drift at different flow velocities and established species specific return rates. Species on the lotic end of the gradient had highest return rates at high flow velocity and used active behaviour most efficiently to return to the bottom from drift. The observed gradient of flow velocity tolerance and species specific abilities to settle from drift indicate that, in addition to dislodgement, the process of returning to the bottom is of equal importance in determining flow velocity tolerance of Trichoptera species.
Highlights
The process of macroinvertebrate drift in streams is characterized by dislodgement, drift distance and subsequent return to the bottom
The observed gradient of flow velocity tolerance and species specific abilities to settle from drift indicate that, in addition to dislodgement, the process of returning to the bottom is of equal importance in determining flow velocity tolerance of Trichoptera species
The species can be ordered along a range based on their tolerance threshold (R [ 0.85) for flow velocity from low to high tolerance: H. radiatus, L. lunatus, A. nervosa, L. rhombicus, C. villosa, M. sequax
Summary
The process of macroinvertebrate drift in streams is characterized by dislodgement, drift distance and subsequent return to the bottom. The fate of most dislodged organisms is poorly understood (Palmer et al 1996; Downes and Keough 1998; Lancaster 2008) and abilities of invertebrates to use behavioural moves to end drifting are scarcely documented (Lancaster et al 2009; but see Oldmeadow et al 2010), despite the importance of movements to colonize unexploited habitats (Rice et al 2010). We hypothesized that all species, being benthic invertebrates, use active behavioural moves to do so, but that drifting specimens of species from lotic environments can return to the stream bottom at higher flow velocities than species from lentic environments. To test this hypothesis, we performed experiments in a controlled laboratory environment, in which flow velocity was manipulated
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