Forestry impacts and the vertical distribution of stream invertebrates in south-western Australia

1. Vertical distributions of invertebrates (> 53 mu m) were compared between two logged and two undisturbed headwater streams in south-western Australia. The abundance and composition of invertebrates from core samples (4 cm diameter, 30 cm depth) were determined at intervals of 0-1 cm 1-5 cm 5-15 cm and 15-30 cm. 2. In addition to examining the effects of clearfell logging, this study provides the first description of the interstitial communities of Australian sandy streams. The interstitial fauna of the undisturbed streams were concentrated in the upper 5 cm of the bed and were numerically dominated by nematodes, a characteristic more typical of marine and lentic habitats than lotic systems. 3. The invertebrate community structure was substantially altered in the logged streams, with fewer taxa collected than in undisturbed streams. Invertebrate densities in the logged and undisturbed streams did not differ in the upper 5 cm of the bed, but, below this, densities were significantly lower in the logged streams. Increased sedimentation did not appear to be responsible for the differences in community structure between logged and undisturbed streams. 4. The impact of clearfell logging to the extent shown here has not previously been demonstrated in south-western Australia. As a consequence it is strongly recommended that sampling of the benthic meiofauna is included in future biomonitoring protocols for the sandy streams of this region.