Diel changes in the benthos of stones and of drift in a southern Australian upland stream

Abstract

Diel changes in the density of the fauna of stones and of drift were investigated in the Toorongo River, an upland river of southern Australia . The densities of the ten most common taxa and of the total fauna in the drift and on the stones were negatively correlated, with 16 out of 33 cases being significant (p < 0 .05) . Five of the ten most common taxa displayed a general trend of reaching day-time peaks in the benthos (11 out of 15 cases) and night-time peaks in the drift (10 out of 15 cases) . The total density on the stones reached a significant peak in the day-time while the total drift density peaked at night .

Diel epibenthic activity of mayfly nymphs, and its nonconcordance with behavioral drift1

“…For any animals that exhibit such escape behavior, it seems plausible that removal of a stone or tile by the investigator would cause most individuals to be found on the underside. Moreover, because we also observed that Cinygmula was somewhat less easily disturbed under dim red light than in full daylight, it is possible that an investigator scraping the tops of stones, as did Graesser and Lake (1984), will catch relatively more such individuals by night than by day. In any event, we suggest that direct observations by an investigator on a platform above the stream may provide more useful information than the removal or scraping of stones.…”

Relationship between current velocity, depth and the invertebrate community in a stable river system

“…These models of habitat suitability, reflecting the complex interaction of velocity, depth and substrate, aim to predict the use of the benthic habitat and the distribution of populations (Statzner et al, 1988). Additional parameters which affect invertebrate density and variety include flow-related phenomena, such as drift, as they affect life in certain stages (Waters, 1972;Muller, 1974;Graessner & Lake, 1984), substrate composition (Statzner,198 1 a) and sizerelated flow preferences, according to oxygen consumption (Kovalek, 1978).…”

Colonisation patterns of mayfly nymphs (Ephemeroptera) on implanted substrate trays of different size

“…Nymphs were able to colonise either through drift or by directed or random movements over the substrate. Baetis dominated the drift and other species were effectively absent (see also Bailey, 1965;Anderson & Lemkuhl, 1968;Neveu, 1980;Bird & Hynes, 1981;Graesser & Lake, 1984). This can largely be related to morphology and behaviour, so that one can, for example, classify mayfly into rare passive drifters (e.g.…”

“…Invertebrate movements involved in colonisation and redistribution are normally attributed to one of four possible mechanisms; downstream drift, aerial sources, upstream and vertically directed movements (Williams & Hynes, 1977), but random lateral movements can contribute a fifth mechanism, especially when new areas, such as implanted substrates, become available within populated habitats. Downstream drift is usually considered to be the most important colonisation/redistribution mechanism (Townsend & Hildrew, 1976;Bird & Hynes, 1981;Graesser & Lake, 1984), although the propensity to drift is not the same in all species (Chaston, 1972;Turcotte & Harper, 1982;Kohler, 1983;Allan, 1984). Other studies have demonstrated that movement on, or in, the substrate can also contribute significantly to overall redistribution of benthos (e.g.…”