The Importance of the Thukela River Estuary, East Coast of South Africa, for the Biology of the Near-Shore Environment and Associated Human Aspects: A Review

The Thukela is the largest river on the KwaZulu-Natal (KZN) coastline, located at the South-Western edge of the Indian Ocean. This coast and the KZN Bight, where the Thukela meets the ocean, is considered meso-oligotrophic with distinct sources of nutrients entering the system. These sources are a series of oceanographic phenomena, including an upwelling cell, and several estuaries, the largest of which is the Thukela River estuary. The shallow Thukela Bank, formed as a sediment plume just off the Thukela estuary mouth, is the major site of several fisheries, notably the prawn trawl and line fisheries. Riverine influence has long been thought to be important for this fishery, but oceanographic research has, until recently, suggested that the main ecosystem driver was the upwelling cell. However, recent studies have shown that the biology of the Bight is primarily maintained by riverine organic matter and nutrients, mainly from the Thukela River. This input has helped support subsistence, recreational and commercial fisheries in one of South Africa’s most populated provinces. Despite the evidence of the Thukela’s ecological importance for the marine environment, the possibility of increasing water abstraction from the Thukela catchment to meet the needs of a growing population has been considered in water-stressed South Africa. Policy makers will increasingly have to face trade-offs between water demands for human consumption and marine ecological functioning, which are likely to be complicated by uncertainty surrounding future climate change effects on the river and its associated marine ecosystems. This review examines the role played by the Thukela estuary, amongst other estuaries in the Bight, and assesses their overall importance for the area from an ecological and human perspective.