Short-term colonization dynamics of macroinvertebrates in restored channelized streams

Macroinvertebrate colonization of restored rivers is a function of dispersal into the restored reach and its suitability for population establishment. To maximize potential for colonization success, spatial considerations such as distance to colonizer source pools and dispersal pathways must be included in restoration planning. Unfortunately, the dispersal abilities of macroinvertebrates and ecological importance of different dispersal modes for colonization are still poorly understood. We used a field experiment that controlled colonization by passive drift and allowed distinction between active upstream aquatic and active/passive aerial dispersal, thus testing their differential importance during colonization of experimentally restored stream reaches. Two agricultural streams emanating below culverts were longitudinally separated along the first 30 m and one stream side each was covered with a fine-mesh net to limit aerial dispersal. Colonization of manually disturbed background and experimentally introduced cobble substrate was investigated over 6 months. We found that upstream in-stream dispersal, especially in these agricultural streams, can be rapid (days) and play an important role in the short-term colonization of restored streams. We conclude that a landscape perspective, in addition to in-stream measures, must be considered when attempting to restore streams dominated by agricultural and urban land use that constrains available species pools and limits dispersal pathways.