INVERTEBRATES IN THE ORANGE RIVER, WITH EMPHASIS ON CONSERVATION AND MANAGEMENT

Summary

Distribution and abundance of aquatic invertebrates in the lower 1800 kilometres of the Orange River is examined in relation to the conservation and management of the Orange River. Data are based on published information and surveys conducted during research into blackfly control, conducted between 1991 and 1996.

The river is characterised by low numbers of species, reflecting the historically seasonal nature of the river. The fauna is dominated by filter-feeders, highlighting the importance of fine particulate material (bacteria, phytoplankton and detritus) in the ecology of the river. No taxa are considered endemic, although the present day distribution of the blackfly S. gariepense is almost certainly restricted to the Orange River. At least three species have probably disappeared from the Orange River in recent years, one is endangered, one is a serious pest, at least fourteen are potential disease vectors, and two are considered invasive. New records for South Africa include five species of Chironomidae and one of Trichoptera.

The middle and lower Orange River is biogeographically isolated, and therefore highly vulnerable to change. Important ecological components of the river include riparian trees, floodplains and rapids. It is recommended that high priority should be placed on the protection of riparian vegetation, and strict control should be imposed on the development of artificial levées. At least one representative and undeveloped floodplain area should be set aside as a conservation area. Furthermore, a dam built directly downstream of Lake van der Kloof, to buffer the effects of hydro-electric pulses, would be highly beneficial.

Keywords:

• Orange River
• invertebrate
• functional feeding
• impoundment
• blackfly
• Simulium
• conservation