Experimental manipulations were conducted in Carnation Creek, British Columbia, to determine the response of macroinvertebrate distribution and abundance to differences in detritus source and quantity. Four treatments (no detritus, low hemlock (Tsuga heterophylla), low alder (Alnus rubra), high alder) with a standardized substrate were established in a riffle and left for 28 d. Densities and/or biomasses of 12 of the 20 colonizing macroinvertebrate taxa were significantly different among the detritus treatments. Microbial activity, detritus processing, and macroinvertebrate abundances were highest in substrate patches with alder detritus. Compared with the no detritus and low hemlock treatments, the low alder treatment increased the abundances of nine taxa and decreased three taxa, while the high alder treatment increased the abundances of six taxa and decreased six taxa. Thus, detritus source and quantity strongly influenced macroinvertebrate community composition within the streambed. Although most of the macroinvertebrates in all treatments were either collector–gatherer or shredder detritivores, these macroinvertebrates responded to changes in detritus in a species-specific manner. Therefore, the Carnation Creek experiments emphasize the importance of interstitial detritus in the substrate as a factor that influences the microdistribution of the benthos at the species, rather than trophic feeding, assemblage level.
Species-specific decomposition rates of beach-cast wrack in Barkley Sound, British Columbia, Canada
