Spatio-temporal attributes of water temperature and macroinvertebrate assemblages in the headwaters of the Bushmans River, southern Drakensberg

Currently, there is little understanding of the controls that instream thermal limits and hydraulic biotype diversity have on macroinvertebrate assemblages, particularly in association with changing altitude within given southern African mountain drainage systems. Thus, the aim of this research was to examine aquatic macroinvertebrate assemblage changes in response to spatial and temporal geo-hydrological contexts (temperature and hydraulic biotype) along the upper Bushmans River, southern Drakensberg. Instream temperature was continuously logged at 3 altitudes (1 760, 2 030, 2 280 m amsl) along the Bushmans River to the east of the Great Escarpment, and in the headwaters of the Sani River (2 860 m amsl) to the west of the escarpment, for the period January–May 2007. Aquatic macroinvertebrates were sampled during early December 2006, late March 2007, and late May 2007. The study demonstrates that decreasing water temperatures, both spatially (with increasing altitude) and seasonally (from summer to winter), and/or decreasing diversity of hydraulic biotypes associated with stream-channel narrowing in Drakensberg rivers/streams, are associated with a general decrease in the absolute number of macroinvertebrate families, a lower dissimilarity coefficient along the Bushmans River altitudinal transect, and a decreasing variance in the numbers of macroinvertebrate families across various hydraulic biotypes.