The eThekwini coastline is 98 kilometres in length, and incorporates 16 estuaries ranging from the uThongathi in the north to the iMahlongwa in the south. The estuaries within this area are made up of 13 temporarily open/closed estuaries, two permanently open estuaries (uMkhomazi and uMngeni) and one estuarine bay (Durban Bay).
Among the most important goods and services delivered by these ecosystems are:
• the provision of nursery grounds for estuarine dependent marine species
• habitats for species confined to estuaries
• refugia for birds
• nutrient cycling
• supply of nutrients to the coastal environment
• sediment supply to the coastal environment
• water supply
• flood mitigation
• waste treatment and
• recreational activities
Lying at the interface between two environments, estuaries experience dramatic changes in the abiotic environment (e.g. floods and tidal influence). It is these sudden changes which exclude many species from estuaries, resulting in relatively low diversity. Nevertheless, those species which are tolerant of abiotic fluctuations are able to exploit a highly productive environment from which many competitors are excluded.
Estuaries are consequently characterised by high densities of biota, but relatively low species diversity when compared with coastal and oceanic environments. Primary producers in these systems range from microscopic algae to the more charismatic mangroves. Representatives from the animal kingdom include zooplankton, benthic invertebrates, fish and birds. The latter three represent the major focal point of the MER study. Detailed methodology is available in the full report “Estuaries of Durban”.