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# of Endemic Species
Major Habitat Type:
xeric freshwaters and endorheic (closed) basins
Liz Day, The Freshwater Consulting Group, Cape Town, South Africa
Paul Skelton, South African Institute for Aquatic Biodiversity, Grahamstown, South Africa
Tree-lined fossil river beds and ephemeral, endorheic pans dot the semi-arid landscape of the Karoo ecoregion. The pans include the Verneukpan-Grootvloer system (Barnes 1998a), one of a series of four major pan systems found in southern Africa (Baard et al. 1985). The ecoregion as a whole includes two distinct terrestrial habitat types (Lowe-McConnell 1996): the succulent Karoo, which contains the region known locally as Namaqualand, located on the west coast of South Africa; and the more easterly Nama Karoo (Branch & Braack 1989). The ecoregion is located almost entirely within the Northern Cape province of South Africa.
Drainages flowing into:
The succulent Karoo is separated from the Nama Karoo by the Bokkeveldberg Mountains, and its rivers drain either directly into the Atlantic Ocean (e.g. Groen River) or into the Olifants River, a perennial system immediately south of the ecoregion.
Main rivers or other water bodies:
The Nama Karoo is traversed by numerous intermittent rivers, including the Carnarvonleegte, Vis, and Sak. The Sak originates in the Nuweveldberge mountains, is joined by the Vis River, and flows into the vast panlands of Brandvlei. Beyond Brandvlei to the north, the Sak flows into Grootvloer Pan — a large, flat, alluvial floodplain that, during high summer rainfall periods, links the Sak River to the Orange River in the north. By contrast, Verneukpan, a system immediately east of Grootvloer, is an internal drainage basin (Lloyd & Le Roux 1985). Carnarvonleegte is one of many episodic rivers that flow into the Verneukpan system. Like Grootvloerpan, Verneukpan may, when full, also provide a passageway to the Orange River, via the Hartbeesrivier in the north. Verneukpan, measuring some 33.5 km long and 11 km wide, is the largest pan in the ecoregion and in all of South Africa (Lloyd & Le Roux 1985). Other major pans in this area include Brandvlei, Flaminkvlei, and Vanwyksvlei.
The succulent Karoo and Nama Karoo each occupy distinct climatic zones, the former falling within the winter rainfall region, and the latter within the summer rainfall region (Harrison et al. 1997). Rainfall in both biomes is unpredictable, patchy, and low; the succulent Karoo averages 20-290 mm per year, and the Nama Karoo averages 100- 520 mm (Lovegrove 1993). Temperatures also fluctuate dramatically, both daily and seasonally. Winter days are cool to mild, while nights are subject to frequent frost; summers are hot with temperatures reaching 45°C (Barnes 1998a).
Pans such as Verneukpan and Grootvloerpan reach depths of up to 1.2 m during wet periods, though this happens rarely. For example, Verneukpan contained substantial water only five times during the period from 1885 to 1985 (Baard et al. 1985). In the succulent Karoo, surface flow in the coastal-draining rivers is also intermittent, as most of the little runoff that the rivers receive is absorbed by the sandy river beds (Heydoorn & Grindley 1981).
Across the ecoregion, water in the rivers and many of the pans tends to brackish or even saline conditions, particularly toward the end of the wet season (Channing 1987). Closed for years at a time, the estuaries of rivers such as Groenrivier are saline to hypersaline, becoming fresher only after being scoured open by occasional floods (Heydoorn & Grindley 1981).
In the succulent Karoo, the winter rainfall regime prevents the widespread growth of trees and promotes an abundance of sclerophyllous shrubs (Harrison et al. 1997). The vegetation of the Nama Karoo, by contrast, is characterised by dwarf shrubs and grasses (Lovegrove 1993). Vegetation on pans such as Verneukpan include species such as Rhigozum trichotomum, Zygophyllum retrofractum complex, Lycium schizocalyx, L. oxycarpum, Pteronia mucronata, Stipagrostis spp., and Eriocephalus aspalathoides (Lloyd & Le Roux 1985).
Dry for most of the year (Barnes 1998b), riverbeds in the Nama Karoo descend sharply from escarpments to meander across the flat plains of the Central Plateau. Lined by belts of riverine Acacia karoo thicket, the riverbeds create a network of riparian habitats that extends across the landscape (Barnes 1998b). Other riparian species include Tamarix usneoides and Euclea, Ozoroa,and Acacia shrubs (Barnes & Anderson 1998).
The Grootvloer-Verneukpan system is the most outstanding wetland feature within the Karoo ecoregion (Baard et al. 1985). The only link between the Orange and the Sak River systems, Grootvloer plays an important role in fish migrations, allowing the free interchange of indigenous fish (e.g. smallmouth yellow fish, Barbus aeneus, and moggel, Labeo umbratus) as well as other aquatic organisms between these two river systems during periods of high summer rainfall (Lloyd & Le Roux 1985).
The fish fauna is depauperate, with only four species known from its waters (B. aeneus, B. anoplus, L. umbratus, and L. capensis). Pools along the Sak River provide refugia for these species during dry periods, from which they may disperse under more favorable conditions (Hocutt & Skelton 1983).
Other noteworthy aquatic biotic elements:
Aquatic fauna are able to withstand long periods of drought in a state of diapause. Among invertebrates, diapause is usually endured by the egg. Once wet conditions occur, the eggs hatch quickly and the animals mature rapidly, often reproducing asexually several times during the short wet season, and only reproducing sexually as conditions deteriorate and the wetlands dry up. The sexually reproductive stages of the life cycle produce fertile eggs, which are able to undergo diapause. Examples of invertebrates found in the pans include species of anostraca (e.g. Streptocephalus sp.), notostraca (e.g. Triops namaquensis), conchostraca (e.g. Eocyzicus gigas), cladocera (e.g. Daphnia gibba) and ostracoda (Lloyd & Le Roux 1985).
Standing water in the Karoo is a rare habitat, and the response of wetland- or riverine-associated animals in the ecoregion is to move to water wherever and whenever it occurs (Vernon 1986). Temporary water in the pans creates an attractive habitat for birds, and although there are no endemic waterbirds in the Karoo, this ecoregion provides an important area for the nationally rare black-necked grebe (Podiceps nigricollis)and black-winged stilt (Himantopus himantopus) (Vernon 1986). Perennial water at estuaries such as Groenrivier make these extremely important wetland oases for water-associated regional and Palearctic migrant birds traversing the succulent Karoo coastline (Heydoorn & Grindley 1981). Frogs occurring in these areas are largely restricted to opportunistic taxa, though several species are endemic to the succulent Karoo (e.g., namaqua caco, Cacosternum namaquense, and paradise toad, Bufo robinsoni (Harrison et al. 2001)). These species have adaptations that allow them to survive long periods without water in the adult stage. Larval stages are usually very short, allowing the frogs to take advantage of short wet periods (e.g. among the cacos – (Passmore & Carruthers 1995)). During hibernation, metabolic rates are drastically reduced. The ecoregion supports a low richness of Odonata with about 35 species of mostly eurytopic, widespread species.
Justification for delineation:
This semi-arid ecoregion is defined by the succulent Karoo and Nama Karoo regions and is characterized by a depauperate aquatic fauna with a southern temperate (Cape) ichthyofauna (Skelton et al. 1995). The rivers of the Karoo ecoregion flow through an area interpreted as the relict channels and overbank deposits of large meandering mixed-load rivers. These rivers had their headwaters in the wetter Gondwanide mountain catchments in the south some 255 million years ago (Smith 1987). The floodplains supported a diverse fauna of mammal-like reptiles, many of which have been preserved in fossilized alluvial deposits (Smith 1993). The more recent paleo-history of the Karoo ecoregion can be interpreted from its fish fauna. The Orange River system forms a focus of distribution for several near-endemic lineages, with the distributions of Barbus aeneus, B. anoplus,and Labeo umbratus overlapping into the Karoo ecoregion (Skelton 1986b, 1994). Species such as B. anoplus also overlap into the Olifants catchment, and Skelton (1986a) suggests that the faunal association between the Orange and Olifants Rivers probably relates to the period when the Upper Vaal-Orange drained via the Olifants mouth (from Paleogene to late Oligocene-early Miocene times), rather than via the present Orange mouth. In addition, the escarpment edge and its associated micro-climate forms an important biogeographic refugium, with relict populations of taxa that are associated with the moist montane grassland of the escarpment edge or regions of deep alluvial sands along the old river courses. Examples of these include amphibians like Cacosternum namaquense (Branch & Braack 1989).
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