VARIABILITY IN THE INVERTEBRATE FAUNA OF AN INTERMITTENT STREAM OVER THREE CONSECUTIVE MIDSUMMER PERIODS

Abstract

Summary Non-perennial rivers in semi-arid regions are exposed to unpredictable and highly variable rainfall and hydrology which can have considerable effects on faunal organisation at different scales. Spatial and temporal dynamics in the aquatic invertebrate fauna of an aseasonal intermittent river in the Eastern Cape, South Africa, were studied over three consecutive midsummer periods. Taxonomic composition varied widely from month to month and between years. Faunal abundances were generally low, and spatial distribution was highly heterogenous. Most of the abiotic variables measured remained within a narrow range over the study period, and only current speed in individual biotopes could be linked to biotic organisation. Faunal similarities were greatest between samples collected during similar hydrological conditions (rather than during similar times of the year). These findings suggest that rainfall and hydrology are major determinants of biotic organisation in this section of the river. The erratic n...