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There are few places on this blue planet that can match the marine diversity found along the shores of Southern Africa. Two very different oceanic currents flank the coast of the southern tip of the African Continent. The west coast of Southern Africa is surrounded by the cold Benguela Current and on the east coast the warm Agulhas Current moves south from the tropics. These two currents create not only two radically different marine environments but also shape the terrestrial ecosystems and the human settlements along the South African coast.
The cold Benguela Current host one of the largest wind driven upwelling systems in the world, as the dominant and strong south easterly winds push coastal surface waters offshore forcing deep, cold and rich-nutrient waters to wells from the depth. When this cold soup full of nutrients reaches the sunlight at the surface it triggers one of the richest marine environment on earth dominated by large production of plankton and massive kelp forests that fringe the rocky shallow coast. Giant kelp plants dominate the shallow reefs along the Benguela and it is under the shelter of this golden forest that there are a myriad of life with many endemic species. The abundance of kelp also feed the shores as plants and particulate seaweed fuels grazers, filter feeders and scavengers waiting on the rocks and sandy beaches. The west coast of South Africa has some impressive records as the world largest biomass of marine flesh of grazers per unit of rock.
On the east side of Southern Africa the warm, fast flowing current moves south from the Mozambique Channel. This is the intense Agulhas Current of about 100km wide and surface water reaching speeds of 2 meters per second. The Warm Agulhas Current creates a much benign environment as the warm ocean releases more moisture into the air generating more precipitation and creating a much greener landscape on land. Many more rivers enter the sea compared to the west coast and many more people settle along these shores, as fresh water is more abundant. For the first time semitropical flora and fauna is seen along this coast. The first large mangrove forests are found along the Mgazana Estuary on the Wild Coast.
During the months from May to July, the cooler Benguela current strengthens and moves up towards the east coast of South Africa (termed the ‘Benguela counter current) and the warm Augulas current weakens and flows off the continental shelf. This cold counter current ‘finger’ of the Benguela current extends northwards along the eastern cape of South Africa, and up into the KwaZulu-Natal province. It is this cool northwards current that opens a migratory pathway for the sardines to move northwards towards KwaZulu-Natal.
Some oceanographic variables have been found useful for describing conditions influencing sardine presence.
Other conditions associated with sardine presence are: