The marine ecoregions of the South African exclusive economic zone are a set of geographically delineated regions of similar ecological characteristics on a fairly broad scale, covering the exclusive economic zone along the South African coast. There were originally five inshore bioregions defined over the continental shelf and four offshore bioregions covering the continental slope and abyssal regions. These bioregions were used for conservation research and planning. They were defined in the South African National Spatial Biodiversity Assessment of 2004. The South African National Spatial Biodiversity Assessment of 2011 amended this to reduce the number of regions to four inshore and two offshore and rename them as ecoregions.
The exclusive economic zone
An exclusive economic zone (EEZ) is a sea zone prescribed by the United Nations Convention on the Law of the Sea over which a state has special rights regarding the exploration and use of marine resources, including energy production from water and wind. It stretches from the baseline out to 200 nautical miles (nmi) from its coast. The term does not generally include either the territorial sea or the continental shelf beyond the 200 nmi limit. but in this context territorial waters are included. The difference between the territorial sea and the exclusive economic zone is that the first confers full sovereignty over the waters, whereas the second is merely a "sovereign right" which refers to the coastal state's rights below the surface of the sea. The surface waters of the EEZ beyond territorial waters are international waters.
History The first mapping of South African marine habitats was done in a series of workshops led by the NSBA marine team culminating in a marine biodiversity assessment report in of the South African National Spatial Biodiversity Assessment of 2004. This indicated 34 marine biozones extending from the supratidal zone to the border of the exclusive economic zone. They allow for future refinement where necessary. Nine South African marine bioregions were defined in the South African National Spatial Biodiversity Assessment (NSBA) 2004. The five inshore bioregions of 2004 were consolidated to four in the 2011 assessment. The Namaqua and southwestern Cape inshore bioregions became the southern Benguela shelf ecoregion. Similarly the Indo-Pacific offshore bioregion, the South-west Indian offshore bioregion, and the West Indian offshore bioregion were combined to become the Southwest Indian ecoregion, reducing the four offshore bioregions to two deepsea ecoregions. The other bioregions were renamed to ecoregions. The resulting regions are: Benguela, Agulhas, Natal, and Delagoa ecoregions, which include the coast, continental shelf and shelf edge, and the Southeast Atlantic and Southwest Indian ecoregions include the upper and lower continental slope and abyssal regions.
The regions
Depth zones The regions are divided into benthic depth zones. Along the coastline there are supratidal, above the high-water mark, intertidal between high and low water, shallow photic, or subtidal shoreface, where there is turbulence and enough light for seaweeds to flourish, down to about 10 m, deep photic, where there is less light, down to about 30 m, and sub-photic (lightless) zones, down to the edge of the continental shelf, which varies from about 400 m in the northern part of the west coast, to 200 m in the Agulhas region, 100 m off Natal, and can be shallow as 50 m in the Delagoa bioregion. The shelf break is defined by the slope angle of the seabed. The offshore regions include upper slope, from the shelf break down to about 1800 m, lower slope, and abyss, below 3500 m. The end boundaries of the supratidal zone do not generally coincide with the bioregion boundaries.
Inshore regions Five inshore marine bioregions that extend from the shoreline to the break of the continental shelf were defined. Boundaries between them are difficult to define, and overlaps between regions are accepted, because available species data may indicate large sections of coast with few endemics, and many species are found spread across more than one region.
West coast
Benguela ecoregion
This is the region comprising the consolidated Namaqua and South-western Cape bioregions.
Namaqua bioregion
This is a cool temperate region between Sylvia Hill just north of Lüderitz in Namibia to Cape Columbine. Sylvia Hill is the northern boundary of a large upwelling cell. The bioregion has large-scale intensive upwelling and nutrient rich water, and the cold Benguela current. The region is known for low oxygen events and it contains extensive mud banks and a relatively wide continental shelf. It is a productive bioregion and supports major commercial fisheries. In the 2011 assessment it was combined with the South-western Cape bioregion to form the Benguela ecoregion.
South-western Cape region
This region has a relatively narrow continental shelf. There is a change in geology at Cape Columbine which marks the northern extent of the exposed granite, and there is less offshore mud habitat south of this break. This region includes the two underwater canyons, Cape Point Valley and Cape Canyon, and there are large areas of rocky reef. The change in biology at Cape Columbine is indicated by change in seaweed and intertidal communities. There is less tendency for oxygen deficient bottom water than in the area further north. This region supports trawl and longline fisheries for hake, pelagic fisheries for anchovy, pilchard and roundherring, and a longline shark fishery. The break at the south-eastern end of the region is at Cape Point, where it is distinct in the inshore and tidal habitats, but the change in deeper water tends obliquely to the south-east, and is more diffuse, due to mixing of the Benguela and Agulhas currents between these regions. In the 2011 assessment it was combined with the Namaqua bioregion to form the Benguela ecoregion.
South coast
Agulhas region
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