Mobility of stream invertebrates in relation to disturbance and refugia: a test of habitat templet theory

The rate of recolonization of artificially denuded substrata by benthic macroinvertebrates was investigated in 7 southeastern England streams that differed in disturbance frequency and refugium availability. Disturbance frequency and refugia were estimated from observation of substratum movements and shear stress distributions, respectively. Thus, high-refugium sites had a high proportion of low shear stress spots at high discharge, whereas low-refugium sites had a low proportion. Colonization was estimated experimentally using wide-meshed cages containing washed substratum, which remained in the stream for 2 or 7 d. Natural and recolonized benthic assemblages were ordinated, and colonization rate was estimated from Euclidean distances. Macroinvertebrate colonization rate (i.e., mobility) increased with disturbance frequency, but only where refugium availability was low. High-refugium sites had faster colonization than low-refugium sites, irrespective of disturbance regime. Higher mobility in high-refugium sites may reflect lower mortality risk from flow disturbance when the physical habitat is heterogeneous. Our study suggests that high refugium availability may reduce the effect of flow disturbance in streams.