|Title||Effects of structural habitat on drift distance and benthic settlement of the caddisfly, Ceratopsyche sparna|
|Publication Type||Journal Article|
|Year of Publication||2002|
|Authors||Holomuzki JR, Van Loan AS|
We conducted two experiments in flow-through, artificial streams to examine how habitat structure affected drift and benthic resettlement of larval hydropsychid caddisflies (Ceratopsyche sparna). In the first experiment, we quantified drift distance and the number of times larvae re-entered the drift in 9.0 x 0.51-in channels with contiguous patches (ea. 2.5-in long) of biofilm-covered gravel, biofilm-covered cobbles (Cladophora), and Cladophora-covered cobbles (+ Cladophora). In the second experiment, we tracked nocturnal movements of larvae after benthic settlement in 2.8 x 0.1-rn channels, each containing one of the three habitat types. In experiment 1, drift distance was (I) greatest in gravel and lowest in cobbles + Cladophora, (2) inversely related to hydraulic roughness of habitats, (3) independent of body size, and (4) similar for live and dead larvae. Average drift distance was relatively short (<2.5 m ), regardless of habitat type. Number of drift re-entries also varied among habitats, being greatest in gravel and lowest in cobbles + Cladophora. No larvae re-entered the drift after settling in Cladophora patches. Results from experiment 2 revealed that drift propensities were higher for larvae in biofllm-covered gravel and cobbles than in cobbles + Cladophora. Larvae remaining in substrate patches (i.e. not drifting) laid fewer draglines in biofilm-covered stones than in Cladophora patches. Extent of benthic movement (i.e., crawling) by non-drifting larvae did not differ significantly among habitats. However, distance moved did differ with flow direction, being 4 x greater downstream than upstream. These results highlight how local substrate and hydraulic conditions interact to affect small-scale movements of caddisfly larvae.