Spatial differences in the distribution of benthic macroinvertebrates along a springbrook

Benthic samples (n = 54) were collected at three sites along an unshaded, first‐order springbrook, 0–3 m, 15–19 m, and 24–27 m below a permanent spring outflow in Mendocino Co., CA, USA. As distance from spring source increased, number of species and species diversity ([Hbar]) decreased, but number of individuals increased. These patterns may have resulted from temperature fluctuation regimes at these three sites, or from a spring source/springbrook ecotone effect. The sericostomatid caddisfly Gumaga nigricula (McL.) had highest population density ([xbar] > 10,000/m2) although seven other populations had mean densities > 100/m2. Distribution of G. nigricula in the springbrook appears to reflect adult oviposition behavior. Zonation patterns and sampling variability in springbrook habitats must be considered in studies that compare first‐order with higher‐order streams (e.g. the River Continuum Concept).