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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

562: Mulanje

Major Habitat Type:

montane freshwaters

Author:

Denis Tweddle, South African Institute for Aquatic Biodiversity (formerly J.L.B. Smith Institute of Ichthyology), Grahamstown, South Africa

Reviewers:

Paul Skelton, South African Institute for Aquatic Biodiversity (formerly J.L.B. Smith Institute of Ichthyology, Grahamstown, South Africa

Countries:

Malawi; Mozambique

Boundaries:

The Mulanje Massif defines the boundaries of this ecoregion, whose headwater streams are isolated from downstream reaches by waterfalls, such that several endemic and relict species occur in and along these highland rivers. The massif is a huge, isolated block of mountains, more than 640 km2 in extent, situated in the southeast corner of Malawi close to the Mozambique border (Eastwood 1979).

Drainages flowing into:

The streams from the massif feed two systems. The northern streams flow into Lake Chilwa, a large (700 km2), shallow lake at the headwaters of the Ruvuma River system. The southern streams coalesce into the Ruo River, a tributary of the Lower Shire River and ultimately the Lower Zambezi.

Main rivers or other water bodies:

High rainfall and an extended rainy season result in many perennial streams flowing from the massif, with important implications for biodiversity. All streams have torrential flow in the rainy season and during the dry months are much reduced in volume, with crystal clear water protected from excessive sedimentation by the forest reserve of the massif.

Topography:

The massif rises abruptly from the flat Phalombe plain (600 m above sea level), to a plateau at nearly 2,000 m, and then up to rocky peaks reaching 3,002 m.

Climate:

The climate of the ecoregion is influenced largely by the equatorial area of low pressure and the position of the Inter-Tropical Convergence Zone (ITCZ). The ITCZ fluctuates in position over Malawi during the rainy season from October to March. The warm northeast monsoon is sometimes unstable, causing heavy storms to develop, especially over the northern facing slopes. Apart from the rainy season, southeast trade winds prevail. The airstream is cool and moist, and forced uplift causes heavy rainfall on the south-east facing slopes, and rainfall in all months, whereas northern Mulanje has a single rainfall maximum in December/January and a fairly long dry season. The southern slopes and plateau average 2,500 mm of rainfall annually and the northern slopes receive about 1,000-1,500 cm. 

Freshwater habitats:

The Phalombe plain is heavily populated and used extensively for agriculture. To the south of the mountain, the Lower Shire rift escarpment causes the Ruo River to drop rapidly to around sea level. This descent includes the 60 m-high Zoa Falls, which effectively isolate the Ruo River fish fauna from the Lower Zambezi fauna found in the lower reaches of the Ruo and in the Lower Shire. The area to the east of Mulanje in Mozambique is poorly known. Isolated smaller mountains in the area may have similar aquatic faunal characteristics to Mulanje.

Fish Fauna:

The Mulanje Massif is effectively an island of montane biodiversity. Its steep slopes and relative inaccessibility, together with the protection afforded by the forest reserves, have safeguarded its natural resources from large-scale exploitation and clearance for agriculture. The high relief results in much more rainfall than in surrounding areas, and thus many more perennial streams. 

On top of the plateau, the only fish species are introduced rainbow trout (Oncorhynchus mykiss) and an indigenous mountain catfish (Amphilius hargeri). The identity of the latter is in doubt as the species was described from one specimen collected on top of the mountain. The type specimen shows slight differences from the common and widespread A. uranoscopus, which is found, together with A. natalensis, at the base of the mountain. Further study is needed of specimens from the top of the mountain to determine the validity of A. hargeri

Description of endemic fishes:

In the Ruo River from the base of the plateau to Zoa Falls, at least ten fish species out of 37 recorded are not found in neighbouring river systems, including at least six probable endemics that are currently under investigation (Tweddle (Tweddle 1985; Tweddle unpublished data; Tweddle & Skelton 1998). Sampling in nearby Mozambique streams that drain to the East African coast is needed to verify the endemism of the Ruo River species. 

Several relict fish species occur in the Ruo as well as in other Zambezi tributaries. These include Hippopotamyrus ansorgii, Barbus eutaenia, B. lineomaculatus,and Opsaridium zambezense. The perennial nature of the streams flowing from the southern slopes of the massif, and the barrier to upstream movement created by Zoa Falls, have allowed the long term survival of a fish fauna that now shows major differences to those of neighboring river systems.

The northern streams from the massif do not contain any endemic fish species, though some have still to be described (Tweddle 1979). These perennial streams form a valuable refuge for the Lake Chilwa fauna during the periodic drying out of the lake (Kalk et al. 1979).

Other noteworthy aquatic biotic elements:

The biodiversity in other floral and faunal groups is also high, although poorly known (Dudley 2000). There are two endemic amphibians, Afrana johnstoni and Arthroleptis francei,and two near-endemics, Nothophryne broadleyi and Hyperolius spinigularis (Broadley 2001), out of 30 known species (Poynton & Broadley 1985, 1986, 1987, 1988). There are at least 22 dragonflies, of which one, Oreocnemis phoenix, is an endemic species within an endemic genus (Wilson 1988). Predaceous diving beetles from the Dyticidae family are also well represented in the fauna (Dudley 2000). 

Justification for delineation:

The massif is a quartz-syenite and granitic plutonic intrusion(s), uplifted, fractured and eroded. Larger river valleys are truncated at the edge of the plateau, forming high waterfalls. Waterfalls on the Ruo River, for example, descend 200 m in a single fall. The plateau is surrounded on many sides by sheer rock walls up to 1,700 m in height (Chapman 1962; Dudley 2000). Floristically, Mulanje belongs to the Afro-montane regional centre of endemism (White 1983).

Level of taxonomic exploration:

Fair. The fish fauna is generally well known, though further sampling is needed as some species are known only from few specimens (one each in the case of two unidentified Barbus species). Dudley (2000) summarizes information on all other flora and fauna and points out that many groups are poorly collected; further research on these taxa is essential, preferably under the umbrella of the Conservation Trust.

References/sources:

Broadley, D. G. (2001). "An annotated check list of the herpetofauna of Mulanje Mountain" Nyala 21 27-36.

Chapman, J. D. (1962). "The vegetation of the Mulanje Mountains, Nyasaland: a preliminary account with particular reference to the Widdringtonia forests" Zomba, Nyasaland (Malawi): Government Printer.

Dudley, C. (2000)"Freshwater molluscs of the Zambezi River Basin" In Timberlake, J.R. (Ed.). Biodiversity of the Zambezi Basin wetlands. (pp. 487-526) Harare, Zimbabwe: Biodiversity Foundation for Africa, Bulawayo/The Zambezi Society.

Eastwood, F. (1979). "Guide to the Mulanje Massif" Johannesburg, South Africa: Lorton Publications.

Kalk, M., McLachlan, A. J., et al. (1979). "Lake Chilwa: Studies of change in a tropical ecosystem. Monographiae Biologicae, vol. 35" The Netherlands: Dr. W. Junk.

Poynton, J. C.,Broadley, D. G. (1985). "Amphibia Zambesiaca 1. Scolecomorphidae, Pipidae, Microhylidae, Hemisidae, Arthroleptidae" Annals of the Natal Museum (Pietermaritzburg) 26 503-553.

Poynton, J. C.,Broadley, D. G. (1988). "Amphibia Zambesiaca 4. Bufonidae" Annals of the Natal Museum (Pietermaritzburg) 29 447-490.

Poynton, J. C.,Broadley, D. G. (1986). "Amphibia Zambesiaca 2. Ranidae" Annals of the Natal Museum (Pietermaritzburg) 27 115-181.

Poynton, J. C.,Broadley, D. G. (1987). "Amphibia Zambesiaca 3. Rhacophoridae and Hyperoliidae" Annals of the Natal Museum (Pietermaritzburg) 28 161-229.

Tweddle, D. (1979)"The zoogeography of the fish fauna of the Lake Chilwa basin" In Kalk, M.;McLachlan, A.J.;Howard-Williams, C. (Ed.). Lake Chilwa: Studies of change in a tropical ecosystem. Monographiae Biologicae, 35. (pp. 177-182 & 440-441) The Netherlands: Dr. W. Junk.

Tweddle, D.,Skelton, P. H. (1998). "Two new species of Varicorhinus (Teleostei: Cyprinidae) from the Ruo River, Malawi, Africa, with a review of other southern African Varicorhinus species" Ichthyolological Exploration of Freshwaters 8 369-384.

White, F. (1983) "The vegetation of Africa, a descriptive memoir to accompany the UNESCO/AETFAT/UNSO vegetation map of Africa, Natural Resources Research 20: 1-356". Paris, France: UNESCO.

Wilson, J. G. M. (1988). "Check-list of dragonflies of Mulanje" Unpublished manuscript

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