Ecoregion Description

576: Zambezian Lowveld

Major Habitat Type:

tropical and subtropical coastal rivers

Author:

Helen Dallas, Freshwater Research Unit, Department of Zoology, University of Cape Town

Reviewers:

Paul Skelton, South African Institute for Aquatic Biodiversity, Grahamstown, South Africa and Brian Marshall, Biology Department, University of Zimbabwe

Countries:

Botswana; Mozambique; South Africa; Swaziland; Zimbabwe

Boundaries:

Perennial and seasonal rivers and associated floodplains, swamp forests, swamps, seasonally inundated pans and grasslands, and coastal lakes of this coastal plains ecoregion support an extremely rich and diverse biota. The ecoregion extends from south of the Zambezi Delta in central Mozambique southwards to and including the Tugela River system in South Africa. 

Main rivers or other water bodies:

The major rivers are the Pungwe, Búzi, lower Save, Limpopo, the lower Inkomati, Umbeluzi, Maputo (including Pongola and Usutu), Mkuze, Hluhluwe and Tugela Rivers, together with several important lakes, namely the lakes of Kosi Bay, Lake Sibaya, Lake St Lucia, Lake Satine, Lake Piti, Poelela Lagoon and numerous other smaller lakes and pans on the southern Mozambican coastal plain. 

Topography:

The geology of the ecoregion consists almost entirely of flat, low-level coastal plain, with pale sandy soils overlying Cretaceous beds. The coastal plain is separated from the Indian Ocean by an almost continual line of forested dunes composed of both Holocene and Pleistocene sand deposits. Alluvial terraces run along the rivers that flow eastwards (Maud 1980). The soils of the eastern part of the plain are very sandy and infertile, whilst those of the western part are inherently fertile to very fertile and the pans often have a high clay and peat content.

Climate:

The ecoregion has a warm and humid climate varying from moist subtropical in the east along the coast to moderately subtropical inland in the western portion of the coastal plain (Maud 1980). Annual rainfall averages 1,000 mm on the coast, decreasing to 600 mm at the foot of the mountain range that forms the western edge of the coastal plains. Along the Limpopo Valley there is an extensive area of very low rainfall (<400 mm per annum; duration of rainy season less than 50 days) (Torrance 1981). The rainfall is extremely variable and drought is the norm although severe floods do occur from time to time.  Rainfall occurs mainly during summer from October to March.

Freshwater habitats:

Towards the coast perennial and seasonal rivers are fringed in places by seasonally inundated pans and lagoons. Swamps and mangroves are common in the lowland reaches and coastal lakes – both estuarine and freshwater – are scattered on the coastal plateau. The northernmost Pungwe, Búzi, and Save Rivers are seasonal rivers, with winter low-flows confined to streams within the channel and summer flows overflowing the channel into adjacent floodplains along their lower reaches. At the coast these rivers form tidal mangrove swamps that are almost continuous from the Pungwe to the Save Rivers, extending 50 km inland at the Pungwe mouth (Hughes & Hughes 1992).

The Limpopo, Inkomati, and Maputo Rivers are all historically perennial although water abstraction in their upper catchments has resulted in periodic cessation of flow in the lower reaches during the dry season. The Limpopo (390,000 km²) has an extensive floodplain in Mozambique with hundreds of seasonal pans and approximately 170 km² of semi-permanent swamps (Hughes & Hughes 1992). The Inkomati River flows through the coastal plains of Mozambique where it forms floodplain swamps. The Pongola River, which forms part of the Maputo/Usutu River System, floods seasonally and its extensive floodplain pans capture and retain floodwater when the river overflows its banks. It forms part of the Ndumo Game Reserve.

Several coastal lakes and lagoons, ranging from freshwater to saline, are scattered throughout southern Mozambique and northern KwaZulu-Natal in South Africa. Of these, Lake St Lucia is the largest (1,555 km²) and possibly the most important saline coastal lake in Africa because of its faunal composition that includes both marine and freshwater elements and because of its extent, biotic diversity, and pristine character (Cyrus 1989). The highly variable nature of this system, in terms of hydrology and salinity ranges, has influenced the biota of the lake, which is diverse and adapted to variability (Cyrus 1989). Others lakes include the estuarine-linked Kosi Bay (110 km²), which is one of the best preserved large estuaries in South Africa, and Lake Sibaya (77.5 km²), which is the largest freshwater coastal lake in South Africa. 

Terrestrial Habitats:

There is a diverse floral landscape that includes open woodland, coastal thicket and palm veld with coastal grassland and dune forest along the coast. Swamp forest, papyrus swamp, marsh and sedge communities, mangrove and riverine woodland occur amongst the numerous wetlands on the coastal plain. The floral assemblage is diverse, and some 2,180 species of flowering plants have been recorded in the St Lucia system alone (Cowan 1995).

Fish Fauna:

Cichlids, cyprinids, gobies and mochokid catfishes dominate the fish of this ecoregion. Many species are found in fresh, brackish and saline waters and several catadromous species spend part of their life cycle in the freshwater coastal rivers and streams (e.g., several members of the Anguillidae family). About 120 freshwater fish species inhabit these waters, of which 22 are endemic. 

Description of endemic fishes:

The endemics are cichlids, cyprinids, gobies, kneriids, eleotrids, aplocheilids, and mochokid, amphiliid, and claroteid catfish. Interesting endemics include several rock catlets (Chiloglanis spp.) that live in rocky riffles and rapids, the Sibayi goby (Silhouettea sibayi) whose largest known population occurs in Lake Sibaya, and the brightly-colored turqoise killifish (Nothobranchius furzeri) that is limited in distribution to the ephemeral pans of the Gonarezhou National Park in Zimbabwe (Skelton 1994).

Other noteworthy aquatic biotic elements:

The extensive inland and coastal wetlands in this ecoregion support a moderately rich aquatic biota. In particular, the aquatic herpetofauna and several groups of aquatic invertebrates are very rich. Large numbers of wetland birds also congregate at the many wetlands that dot the coastline. 

The ecoregion has very rich flora and is globally recognized as a center of plant diversity (www.ccwr.ac.za/wetlands/st_lucia_ris.htm). Lake St Lucia, for example, has some 2,180 species of flowering plants, many of which are rare or endangered species. Because of its high diversity and endemism, the lake is of special value for maintaining the genetic and ecological diversity of the flora of this ecoregion. The Kosi system has a number of rare and threatened plants and has five species of mangrove. 

Eight aquatic or semi-aquatic species of mammal live in and alongside the watercourses in the ecoregion, including the hippopotamus (Hippopotamus amphibius),water mongoose (Atilax paludinosus), southern reedbuck (Redunca arundinum), Vlei otomys or African swamp rat (Otomys irroratus), African marsh rat (Dasymys incomtus), clawless and spotted-necked otters (Aonyx capensis and Lutra maculicollis) and a marine mammal, the endangered dugong (Dugong dugon).Several savanna animals utilize the coastal lakes and swamps seasonally, migrating to them in the dry season when inland pans and rivers are dry.

Avifaunal richness is high; for example, Lake St Lucia supports over 350 bird species and is the most important breeding area for waterbirds in South Africa. The Kosi system has 296 bird species. Among those inhabiting the swamp forests are the African finfoot (Podica senegalensis), white-backed night heron (Gorsachius leuconotus) and Pel’s fishing owl (Scotopelia peli). More than 20,000 waterbirds have been recorded at Lake Sibaya, an important wetland that provides a link between the Kosi Bay and Lake St Lucia systems (Barnes et al. 2001).

The ecoregion is an important destination or stopover for migratory birds and is one of the principal avifaunal breeding areas in southern Africa. Lake St Lucia is of particular importance for congregations of Pelecanus onocrotalus, Sterna caspia, Platalea alba, Phoenicopterus ruber, Anas undulata, A. smithii, Recurvirostra avosetta, and Larus cirrocephalus (Barnes et al. 2001).

The richness of several groups of aquatic invertebrates, including Odonata, Ephemeroptera and Trichoptera, is high. About 150 species of Odonata are known from the ecoregion and Lake St Lucia has 52 species of dragonflies. It also has 115 species of benthic amphipods whereas Lake Sibaya has one endemic copepod (Tropocyclops brevis). A particular species of butterfly, a skipper (Parnara micans), is regarded as endemic to Kosi Bay (Campbell 1969). Richness is also relatively high for freshwater molluscs, with 27 species occurring in the ecoregion, although only one (Eussoia leptodonta) is endemic, and this one is known only from the estuary of the Komati River.

This ecoregion is one of the richest areas for reptile and amphibian species in southern Africa. About seventy amphibians have been recorded in the ecoregion, of which three, Afrixalus delicatus, Hyperolius pickersgilli, and Cacosternum striatum, are endemic. Seventeen species of reptile have been recorded, including the water monitor(Varanus niloticus), African rock python(Python sebae), brown water snake(Lycodonomorphus rufulus), olive marsh snake(Natriciteres variegata sylvatica), northern green water snake(Philothamnus irregularis), common green water snake(P. hoplogaster), forest cobra(Naja melanoleuca) and the Nile crocodile(Crocodylus niloticus). Lake St Lucia and its associated fresh water systems support one of the largest populations of Nile crocodiles on the sub-continent and it is estimated that approximately 1500 individuals over 2 m long are present.

Justification for delineation:

This ecoregion is at the interface between tropical and subtropical African biota and the tropical Zambezian and temperate fish faunas overlap within this ecoregion. The ecoregion is defined by the low-lying portions of the coastal rivers south of the Zambezi Delta to Lake St Lucia. This ecoregion is included within the Zambezian bioregion since the rivers have historically been connected with the Zambezi River (Skelton 1994; Marshall 2000). As one moves southwards, the fish fauna changes from predominantly Zambezian in origin to temperate, with few Zambezian fishes remaining south of Lake St Lucia. The ecoregion is considered part of the tropical east coast region, defined by Skelton (1993), which is characterized by low-gradient mature systems with floodplain reaches(Skelton 1993).

Level of taxonomic exploration:

Fair. Many of the aquatic systems in this ecoregion have been extensively studied, in particular the coastal lakes of South Africa (Whitfield & Blaber 1978a, 1978b, 1978c; Whitfield & Cyrus 1978; Allanson 1979; Bruton & Cooper 1980). However, less work has been completed on the coastal rivers in Mozambique.

References/sources:

Allanson, B. R. (1979) Lake Sibaya. Monographiae Biologicae 36. The Hague, The Netherlands: Dr W Junk.

Barnes, K. N., Johnson, D. J., et al. (2001)"South Africa" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 793-876) Newbury and Cambridge, UK: Pisces Publications and BirdLife International (Birdlife Conservation Series No. 11).

Bruton, M. N.,Cooper, K. H. (1980). "Studies on the ecology of Maputaland" Cape Town, South Africa: Cape and Transvaal Printers.

Campbell, G. G. (1969). "A review of scientific investigations in the Tongaland area of Northern Natal" Trans. R. Soc. S. Afr. 38 305-316.

Cowan, G. I. (1995)"South Africa and the Ramsar convention" In Cowan, G.I. (Ed.). Wetlands of South Africa. (pp. 1-20) Pretoria, South Africa: Department of Environmental Affairs and Tourism.

Cyrus, D. P. (1989). "The Lake St Lucia System - a research assessment" Southern African Journal of Aquatic Sciences 15(1) 3-25.

Hughes, R. H.,Hughes, J. S. (1992). "A directory of African wetlands" Gland, Switzerland, Nairobi, Kenya, and Cambridge, UK: IUCN, UNEP, and WCMC.

Marshall, B. E. (2000)"Fishes of the Zambezi Basin" In Timberlake, J. (Ed.). Biodiversity of the Zambezi Basin wetlands. (pp. 393-460) Harare, Zimbabwe: Biodiversity Foundation for Africa, Bulawayo/The Zambezi Society.

Maud, R. R. (1980)"The climate and geology of Maputaland" In Bruton, M.N.;Cooper, K.H. (Ed.). Studies on the ecology of Maputaland. (pp. 1-7) Cape Town: Cape and Transvaal Printers.

Skelton, P. H. (1993) A complete guide to the freshwater fishes of Southern Africa. South Africa: Southern Book Publishers, Halfway House.

Skelton, P. H. (1994). "Diversity and distribution of freshwater fishes in East and Southern Africa" Annals of the Royal Central Africa Museum (Zoology) 275 95-131.

Torrance, J. D. (1981). "Climate handbook of Zimbabwe" Harare, Zimbabwe: Department of Meteorological Services.

Whitfield, A. K.,Blaber, S. J. M. (1978). "Feeding ecology of piscivorous birds at Lake St Lucia. Part 3: Swimming birds" Ostrich 50 10-20.

Whitfield, A. K.,Blaber, S. J. M. (1978). "Feeding ecology of piscivorous birds at Lake St Lucia. Part 2: Wading birds" Ostrich 50 1-9.

Whitfield, A. K.,Blaber, S. J. M. (1978). "Feeding ecology of piscivorous birds at Lake St Lucia. Part 1: Diving birds" Ostrich 49 185-198.

Whitfield, A. K.,Cyrus, D. P. (1978). "Feeding succession and zonation of aquatic birds at False Bay, Lake St Lucia" Ostrich 49 8-15.