Heterogeneous currents and algal resources mediate in situ foraging activity of a mobile stream grazer

N.L. Poff, J.V. Ward

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    Near-bed current velocities were characterized for topographically-complex substrata concurrently with spatial patterns of algal density and taxonomic composition. Activities of self-marked mobile Agapetus boulderensis (Glossosomatidae: Trichoptera) larvae were examined in relationship to current and algal resources. Near-bed currents alone influenced the distribution and local abundance of individuals in a size-dependent fashion: fifth (final) instar larvae occurred across a velocity range of <5-50 cm s-1, while smaller third and fourth instar larvae were found only at currents ranging from <5-30 cm s-1. Direction of movement on stone surfaces was significantly into or lateral to incoming flow. Rate of movement was inversely related to local current speed and positively related both to temperature and to travel in the upstream direction. Movement rate was inversely correlated with estimated diatom density but positively correlated with densities of green and blue-green algae for larvae on one stone. Gut analysis revealed a significant positive preference by Agapetus for diatoms, particularly Cocconeis placentula, which was overrepresented in the gut. -from Authors
    Original languageUndefined
    Pages (from-to)465-478
    Number of pages14
    Issue number3
    Publication statusPublished - 1992

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