Stream hydraulics and the distribution of microcrustacea: A role for refugia?

Anne Robertson, J. Lancaster, A. G. Hildrew

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1. The relationship between microcrustacean abundance and flow habitat in three contrasting reaches of a single stream was examined.

2. Three methods of characterizing stream hydraulics (shear stress frequency distributions, Froude numbers and mean reach velocity) showed the same pattern among the three reaches, which were subsequently termed ‘fast’, ‘slow’ and ‘medium’.

3. Distributions of epibenthic microcrustacea matched flow characteristics of the three reaches, being most abundant in the slow reach and least abundant in the fast reach. In contrast, densities of three out of four species of interstitial Harpacticoida did not vary significantly with reach, and none of the parameters measured explained much of their between-patch variation in density. Hydraulic conditions at the substratum surface may not affect the distribution of species with interstitial habits.

4. Patterns in the abundance of organic matter (a possible food source) were examined. Measures of organic matter were highly correlated with hydraulic variables, with detritus being most abundant in the slow reach and least in the fast reach. Despite their strong response to reach, local densities of most microcrustacea (including many epibenthic species) did not vary with organic matter. Food for detritivorous microcrustacea may not be limiting in this highly retentive stream.

5. There was some evidence to suggest that different numbers of animals were retained in the three reaches during flow disturbances. One reach may function as a ‘flow refugium’. Models illustrating the processes by which lotic organisms may use flow refugia are presented and provide a framework for future empirical and theoretical studies
Original languageEnglish
Pages (from-to)469-484
Issue number3
Publication statusPublished - 1995

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