MACROINVERTEBRATE ACTIVITY IN THE WATER COLUMN OF BACKWATERS IN AN UPLAND STREAM IN VICTORIA

The activity of benthic invertebrates was monitored in the water colum n of slowly flowing backwaters of the Acheron River during summer. Sam ples were taken throughout 24 h on two occasions, and densities of fau na were compared with densities in drift samples taken concurrently in the main channel. Drift densities were generally higher than those in backwaters, but not by orders of magnitude. Also, drift densities dis played significant diel variation, whereas densities in backwaters did not consistently show such a pattern. Species composition generally d iffered between the two habitats. This brief study demonstrates that b enthic invertebrates do swim in the water column of stream backwaters and that they may use this opportunity for colonization.