LONG-TERM PATTERNS OF INVERTEBRATE STREAM DRIFT IN AN AUSTRALIAN TEMPERATE STREAM

1. Invertebrate stream drift was sampled bimonthly in the Acheron Rive r, Victoria, Australia, over a period of 18 months. Replicated hourly samples were collected over a 25-h period on each sampling date. A tot al of 194 taxa were identified in the drift. However, total drift dens ity was dominated by few taxa. 2. Some evidence was obtained for a sea sonal pattern in drift: this was most pronounced in relative abundance s of individual taxa and the composition of the drift, rather than in total drift densities. Most of the commonly collected taxa reflected t he seasonal pattern of total drift. However, some of the common taxa d id not. 3. A small number of taxa showed behavioural drift, with a noc turnal increase in drift densities. One species of 'Baetis' drifted in high densities over short periods of time around dusk and dawn. It di d not drift in higher densities during the night than during the day. The results emphasize the need for drift studies to be more rigorously designed than is typically the case.