Cape Fold
ID
578
Author(s)
Genevieve Jones, Freshwater Research Unit, University of Cape Town, South Africa
Countries
South Africa
Reviewer(s)
Paul Skelton, South African Institute for Aquatic Biodiversity (formerly J.L.B. Smith Institute of Ichthyology), South Africa
Major Habitat Type
Temperate coastal rivers
Drainages flowing into
Drainages flow into the Atlantic and Indian oceans.
Main rivers to other water bodies
Within the Cape Fold ecoregion, Brown et al. (1996) (Brown et al. 1996)describe five sub-regions, each dominated by different climates and thus resulting in different aquatic ecosystems. The fynbos (bordered by the Orange River in the north and the Atlantic Ocean in the west) and the southern coastal bioregions receive 600-2,000 mm per annum of winter rainfall and support oligotrophic (nutrient poor), peat-stained, acidic rivers. These rivers include the Olifants, Berg, and Breede rivers in the fynbos bioregion and the Bloukraans, Elands, Silwer, Kaaimans, Duiwe, Homtini, and Touws rivers in the southern coastal bioregion. The southern inland bioregion lies to the north of the southern coastal bioregion and includes the Couga, Baviaanskloof, and Olifants rivers. The rainfall is low (200- 600 mm per annum) and the aquatic systems have pH levels in the neutral range, with low conductivities and clear water. The alkaline interior bioregion lies inland of the fynbos and surrounds the southern inland and coastal bioregions. It supports alkaline seasonal or ephemeral waters and includes parts of the Doring, Gamtoos, and Gouritz rivers. The drought corridor bioregion has erratic rainfall and thus supports seasonal rivers, including the Great Fish, Sundays, Kowie, and Bushmans (Van Nieuwenhuizen & Day 2000).
Non-riparian wetlands of the ecoregion are also diverse and include acid sponges, restioid marshes, peat-stained systems, and other perennial and seasonal wetlands. A number of coastal lakes and alkaline saltpans of variable sizes and shapes and important estuarine areas (such as Langebaan Lagoon, Berg River Mouth, and Wilderness Lakes) also occur. Pans, some permanent in wetter areas, are associated with the low-lying Karoo and coastal plain (Silberbauer & King 1991).
Description
Boundaries
Located at the southernmost part of the African continent, the Cape Fold ecoregion is bounded on the south and west by the cold Atlantic Ocean and in the southeast by the warm Indian Ocean. Thus, many of the inland ecosystems experience a strong marine influence. The ecoregion is bound on the northwestern side by the Orange River and in the interior by the arid Karoo. The Cape Fold is a relatively small ecoregion that encompasses a phenomenal diversity of landscape types and correspondingly high levels of biotic diversity and endemism. The diversity of aquatic systems is linked to the different climatic regimes within the area.
Topography
Some areas within the ecoregion rise to 1500 m (Silberbauer & King 1991), but the coastal plain, which reaches an average altitude of 500 m, extends far inland and affects the ecological processes and types of wetlands. The main geological type of the southwestern Cape is Table Mountain Group sandstones, but Malmesbury shales and alluvium areas occur as well (Silberbauer & King 1991).
Freshwater habitats
Compounds such as tannins and phenols derived from fynbos vegetation run into the freshwater systems and result in the so-called “black” waters, which are characteristic of the southwestern Cape (Britton 1991). The temperate acidic waters of this ecoregion are a rare habitat type to which many aquatic organisms have adapted.
Description of endemic fishes
There are about thirty indigenous fish in the freshwater systems of the Cape Fold ecoregion, 16 of which (53 %) are endemic. Eleven of these are critically endangered, three are vulnerable, and one is near-threatened (Skelton 1987). There are two endemic genera, Austroglanis and Pseudobarbus,and the near-endemic Sandelia. Current genetic work indicates that the galaxiid and Sandelia taxa both represent species complexes rather than single species.
Justification for delineation
The ecoregion is defined by the coastal rivers of the southern tip of the continent and is bound on the northwestern side by the Orange River and in the interior by the arid Karoo. Although the history of the area has generally been investigated in connection with the floral kingdom, the same processes would have affected aquatic fauna. The freshwater fish fauna, for instance, is highly endemic and has ancient origins (Skelton 1994). One species complex (Galaxias spp.) has phylogenetic relatives in South America, Australia, and New Zealand and therefore is most probably of Gondwanan age and derivation.The close phylogenetic affinities of other endemic species are uncertain, but it appears that the region is an isolated evolutionary arena.
Level of taxonomic exploration
Extensive systematic and ecological research has been carried out on particular river systems. A few of the larger permanent wetland systems have been well studied (such as The Wilderness Lakes, Langebaan Lagoon, and some urban systems), but there is little understanding of the ecological processes that occur in many others, particularly small and temporary wetland systems.
References
- Britton, D. L. (1991). "Fire and the chemistry of a South African mountain stream" Hydrobiologia 218 pp. 177-192.
- Brown, C. A., Eekhout, S. and King, J. M. (1996) \National Biomonitoring Programme for Riverine Ecosystems: Proceedings of spatial frame workshop\ Pretoria, South Africa. Department of Environmental Affairs and Tourism.
- Cowan, G. I. and Marneweck, G. C. (1996) \South African National Report to the Ramsar Convention 1996\ Pretoria, South Africa. Department of Environmental Affairs and Tourism.
- Shmueli, M., Izhaki, I., Arieli, A., et al. (2000). "Energy requirements of migrating great white pelicans, Pelecanus onocrotalus" Ibis 142 (2) pp. 208-216.
- Skelton, P. H. (1987). "South African Red Data Book - Fishes" South African National Scientific Programs Report 40 pp. 199.
- Skelton, P. H. (1994). "Diversity and distribution of freshwater fishes in East and Southern Africa" Annals of the Royal Central Africa Museum (Zoology) 275 pp. 95-131.
- Van Nieuwenhuizen, G. D. P. and Day, J. A. (2000) \Chapter 2: Freshwater Ecosystems\ In G. D. P. Van Nieuwenhuizen and J. A. Day (Ed.), Cape Action Plan for the environment: The conservation of freshwater ecosystems in the Cape Floral Kingdom> Cape Town, South Africa: Freshwater Research Unit, University of Cape Town.
- Wishart, M. J. and Day, J. A. (2003). "Endemism in the freshwater fauna of the South-Western Cape, South Africa" Verhandlungen Internationale Vereinigung Limnologie 28 pp. 1762-1766.