Spatial and temporal variation in the macroinvertebrate fauna of streams of the northern jarrah forest, Western Australia: community structure

Highest stream discharge occurs during winter (June-November) reducing to negligible flow over late summer and autumn (January-May). Low flows in summer were associated with warm water, lower dissolved oxygen, increased concentrations of cations and, in many cases, lower pH. Temporal changes in abundance, diversity and evenness indicated that the invertebrate fauna became dominated by a few taxa during the summer months. Summer and winter faunas were distinguished at most sites and were associated with seasonal changes in the physical and chemical environment. This seasonality is not typical of stream systems previously studied in Australia. Large spatial differences also occurred over small distances among sites in 2 similar-sized forested catchments. Velocity and depth were highly associated with the observed temporal changes in the fauna, though other variables, including concentrations of cations and water temperature, were also important. Spatial differences were correlated with concentrations of cations which may simply reflect differences in the geologies of the catchments