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. 

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.

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).

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).

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.