Macroinvertebrate movements in a large European river*

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Abstract
SUMMARY. 1. Quantitative variations in downstream movements of benthic macroinvertebrates were studied in a large European river, the Rhône, upstream from Lyon. Artificial substrates were suspended at three depths in the water column, both near a bunk and in mid‐channel, monthly from December 1978 to March 1980. Drift nets were used to determine the diurnal rhythm in drift and to investigate the efficiency of our suspended artificial substrates in capturing the drifting macrofauna.2. Drift densities (number and biomass) reached a maximum during summer, especially near the river bank, and at night. Mean individual weight of organisms was higher close to the bottom and at night.3. Artificial substrates were reliable, but underestimated drift by about a quarter in number and a sixth in biomass. compared with drift nets. Two detailed analyses of the drift distribution across the width of the river revealed similar densities along both banks, and uniformity in the channel as a whole.4. Mean annual drift densities estimated for the section of river were 100 individuals, per 100 m3 and 60 mg dry weight per 100 m3. These densities are similar to those obtained from other temperate rivers.