Experimental colonization of sand, gravel and stones by macroinvertebrates in the Acheron River, southeastern Australia

SUMMARY. 1. The contribution of drift to macroinvertebrate colonization was studied over 10 days using pairs of substratum-filled trays, one suspended above the streambed (and thus able to be colonized by drift only) and one buried flush with the streambed (and thus open to colonization from all directions). Trays were filled with sand, gravel or stones.
2. Colonization of sand-filled trays was rapid, being completed within 24h (i.e. no subsequent change in numbers of individuals per tray); colonization of gravel or stone-filled trays was not completed by the end of the experiment.
3. Drift contributed an average of 86% of the colonizing fauna of the sand-filled trays, 36% of the fauna of the gravel-filled trays and 25% of the fauna of the stone-filled trays. The low contribution of the drift to the gravel and stones is at odds with some studies which, using similar techniques, suggest that drift is the primary source of colonizing individuals.
4. Most individual species showed low contributions by drift to colonization, with the majority having contributions under 66%.
5. Distinct differences were noted between the fauna colonizing the sand-filled trays and those colonizing the gravel or stone-filled trays (which were similar).
6. Several species common in the drift were rare in the colonizing fauna and several species which were common colonizers were absent or rare in the drift.