Bi Coastal


The east coast waters are characterised by the warm waters of the southward flowing Agulhas Current, while those of the west coast are characterised by the upwelling of cold, nutrient-rich waters of the Benguela Current.
Along the southwest and south coast, there is an extensive mixing of water masses. The currents influence the composition of the animal and plant communities along this coastline.
Sandy beaches consist of an unstable sandy bottom layer that is continually modified by waves and currents, resulting in an absence of plants between the tide marks. Yet, a few animal species have adapted to live in this harsh environment.
For example, the plough snail (Bullia sp.) and white mussel (Donax sp.) have adapted by burrowing in the sand. These animals emerge to feed when conditions are relatively mild, or they sit tight in the sand and filter food particles from the seawater with siphons or strainers.
The pink ghost crab (Ocypode ryderi) burrows deeply by day, emerging by night to feed on deposited carrion and small animals. Other animals, such as the leatherback turtle (Dermochelys coriacea), merely visit the intertidal zone to lay their eggs.
The rocky shores that are scattered along the coastline provide a firm foundation for the attachment of plants and animals, but are exposed twice a day by the tides and are often lashed by a strong wave action.
These shores support a great diversity of marine organisms, some of which are commercially significant, for example, mussels, oysters and seaweed.
The intertidal and the subtidal zones provide feeding grounds for many species of fish, some of which are important angling species.
South Africa’s only coral reefs occur in the subtropical waters off the coast of northern KwaZulu-Natal and Maputaland. These particularly fragile environments support an abundant growth of Indian Ocean corals that harbour diverse Indo-Pacific fish fauna. These reefs form a vital link in the overall food web of southeast Africa and play an important role in the distribution of migratory fish.
Commercially important species such as the larger mackerels, couta and kingfishes migrate along the narrow belt of the coral reefs of Maputaland, to reach southern African waters during the summer months.
Lekker Links
South Africa Department of Environmental Affairs and Tourism
Diving with Raggies on Aliwal Shoal Biomes.
Forests; Fynbos; Grasslands; Nama-Karoo; Savannas; Succulent Karoo.
Wetlands.
The west coast is dominated by dense beds of the giant kelps or sea bamboo (such as Ecklonia maxima), which form a calm underwater forest-like habitat and can extend to as much as 3 km offshore. These kelps are extremely productive. Not only are they a major source of food, but they also provide shelter for fish, animals and plants that inhabit calm waters such as the commercially important rock lobster and abalone stocks.
In the open sea, there is no firm base, and organisms must either drift or be able to swim. Examples include the bottlenose dolphin (Tursiops truncatus), the blue-and-gold fusillier (Caesio caerulaureus), the Cape moony (Monodactylus falciformis) and the Japanese bigeye (Pristigenys niphonia), phytoplankton and zooplankton.
The east coast waters are characterised by a greater biotic diversity than the southwest and south coast waters where fewer species occur but in greater numbers. The main focus of commercial fisheries is therefore centered in the more productive waters of the southwest and south coasts.
The cold tidal waters close to the south and eastern coast of South Africa make sharks a common occurrence. Divers come from around the world to South Africa to dive with sharks, such as the ragged tooth shark, Carcharias Ttaurus (or “raggies” as they are locally known).
Despite their large size and fearsome rows of sharp teeth, raggies are docile and allow divers to approach within a few metres. In winter and spring, ragged tooth sharks can be readily seen on the Aliwal Shoal – a submerged reef on the east coast of South Africa, 50 kilometres south of Durban.
Mothers give birth to two live young which spend their first few years in the waters of the Eastern Cape. When they’re old enough, the youngsters join the adults on the annual migration up the east coast to northern KwaZulu-Natal and southern Mozambique. On the way, they spend some time at offshore reefs such as the Aliwal Shoal, where they may engage in courtship and mating.
(Source: South Africa Department of Environmental Affairs and Tourism and WWF)


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