APPLICATION OF THE COMMUNITY DEGRADATION INDEX TO SOUTH-AFRICAN ESTUARIES

A community degradation index has been recently developed which utilized the information contained in the fish assemblages from several North American river basins to describe their relative degree of degradation (Ramm, Wat. Res. 22, 293-301, 1988). We have applied this approach to describe the relative degradation of 62 estuarine and lagoonal systems situated on the Natal coast in South Africa. The 62 systems were first classified into six major groupings based upon eight physical-hydrologic parameters. This classification procedure involved the use of detrended correspondence analysis, two-way classification techniques and principle components analysis. Reference faunal lists were then developed for each of the physical groupings using historical data and by obtaining the consensus of local experts. CDI values were calculated for each system by comparing its reference faunal list with species lists resulting from biological surveys conducted between 1981-1986. Computed values ranged from 0.2 (undegraded) to 8.2 (severely degraded). The most degraded system was one which, through excessive siltation, no longer exchanges water with the sea and has largely lost its estuarine functions. Several interesting examples are presented of the application of the index to planning concerns in Natal Province. © 1990.