Short-term colonisation by macroinvertebrates of cobbles in main channel and inundated stream bank habitats

In small, forested catchments, short rainfall events cause relatively rapid increases in river discharge that inundate previously dry streamside habitats and last for several days. We examined the colonisation and use of such newly inundated habitats by macroinvertebrates in the riffles of a cobble-dominated river over a 4-day period. First we simulated inundation by adding dry river rocks to the main channel of the stream. Second, we observed colonisation of streamside rocks that were inundated following rainfall and subsequent natural spate. Macroinvertebrates colonised rocks in both habitats within 24 h, yet overall macroinvertebrate abundance did not change significantly over the subsequent 3 days. The abundances of common taxa were similar on mid-channel and stream bank rocks but each habitat contained a unique suite of uncommon taxa. Taxon richness was significantly greater on the stream bank rocks, which we attribute to the non-selective colonisation of fauna to avoid high flows in the main channel during the spate. Our study shows that fauna use the stream bank habitat as a haven from high flows in the main river channel, but the fate of the animals colonising this habitat is uncertain. Handling editor: D. Dudgeon