Ecoregion Description

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Species Richness

# of Endemic Species

Threats

583: Madagascar Eastern Lowlands

Major Habitat Type:

tropical and subtropical coastal rivers

Author:

John S. Sparks, Department of Ichthyology, Division of Vertebrate Zoology, American Museum of Natural History, New York, NY, USA

Countries:

Madagascar

Boundaries:

The Eastern Lowlands comprise a narrow strip of land flanking Madagascar’s eastern coast.

Drainages flowing into:

Indian Ocean

Topography:

Rivers flowing through the Eastern Lowlands have relatively flat profiles compared to their steep upper reaches, have moderate to slow flows, and are frequently turbid (probably a result of extensive upstream deforestation).

Climate:

Rainfall along the eastern coast of Madagascar reaches a mean high of approximately 350 mm per month on the Masoala Peninsula and coastal areas immediately to the south, the wettest region of the island (Donque 1972). Precipitation in this ecoregion is, for the most part, evenly distributed throughout the year (Donque 1972).

Freshwater habitats:

Within this narrow coastal plain, rivers often meander and terminate in chains of brackish lagoons (Aldegheri 1972). The substrate in most rivers ranges from coarse gravel to sand or mud, and the water is relatively warm compared to middle and upper reaches of the same rivers. Lowland Pandanus and palm swamps, as well as numerous estuarine habitats along the eastern coast, continue to support native fish faunas.

Terrestrial Habitats:

Fish Fauna:

A single Pandanus and palm swamp within Manombo Special Reserve, on the southeast coast, is the only remaining habitat of Pantodon sp., a small, endemic cyprinodontiform fish of uncertain familial affinity (Sparks 2003). Prior to the discovery of the southeastern Manombo population, which represents a distinct species (Reinthal and Sparks, unpub. data), the cogener P. madagascariensis had only been collected from a single coastal location to the north of Tamatave (a population and species now considered to be extinct).

The lower reaches of eastern drainages are more diverse ichthyofaunally than headwater regions. In terms of endemic taxa, these lower elevation communities are primarily rich in Bedotia, but members of the endemic cichlid genera Paretroplus, Paratilapia, and Ptychochromis are also present.

Other noteworthy aquatic biotic elements:

Madagascar’s eastern rivers and streams are also home to six species of crayfish in the endemic genus Astacoides (Benstead et al. 2003). Recent studies have also revealed tens of new aquatic insect species, indicating that diversity and endemism of aquatic insects is high in this region (Benstead et al. 2000; Benstead et al. 2003). For example, among the Trichoptera a relationship has been established between the eastern rain forest stream habitats and microendemism. The highest species diversity for mayflies on the island is also found in the eastern rain forests, with the number of described species inhabiting Madagascar increasing from 15 in the early 1990s to 100 in early 2002 (Benstead et al. 2003). Frogs are also abundant in this ecoregion with about half of the seventy species being endemic. Several wetlands and forested streams along the coast are also important sites for waterbirds, including Glareola ocularis, Phoenicopterus ruber, the near-threatened Lophotibis cristata , the vulnerable Ardeola idea, and the vulnerable Tachybaptus pelzelnii (Project ZICOMA 2001; IUCN 2002).

Justification for delineation:

The upper and lower eastern basins have traditionally been considered as a single hydrographic region. Based on the results of recent ichthyofaunal surveys throughout eastern Madagascar, however, an elevational disjunct in species distributions has been documented (Reinthal & Stiassny 1991; Sparks & Stiassny 2003). Sparks and Stiassny (2003) record a total of 69 native fish species from basins in the Eastern Lowlands, and 51 species from the Eastern Highlands. In total, 57 native species are restricted to the Eastern Highlands [581] and Lowlands combined, whereas 48 native species are restricted to western basins. Thus, eastern drainages are richer than western basins. Within the eastern basins, the fish assemblages present in highland and lowland habitats differ considerably (Sparks & Stiassny 2003). Taking into account the substantial differences in their respective ichthyofaunal assemblages, the upper and lower eastern basins have been split at the edge of the coastal plain.

Level of taxonomic exploration:

Fair. Of Madagascar’s five major aquatic ecoregions, the Eastern Highlands [581] and Eastern Lowlands are certainly the best studied. This is mainly due to a number of large towns and a network of regularly maintained roads along most of the eastern coast that permit access to these basins.

References/sources:

Aldegheri, M. (1972)"Rivers and streams on Madagascar" In Battistini, R.;Richard-Vindard, G. (Ed.). Biogeography and ecology in Madagascar. (pp. 261-310) The Hague, The Netherlands: Dr. W. Junk.

Project, Zicoma (2001)"Madagascar" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 489-537) Newbury and Cambridge, UK: Pisces Publications and BirdLife International (Birdlife Conservation Series No. 11).

Reinthal, P.,Stiassny, M. L. J. (1991). "The freshwater fishes of Madagascar: A study of an endangered fauna with recommendations for a conservation strategy" Conservation Biology 5 231-243.

Sparks, J. S. (2003)"Pantanodon" In Goodman, S.M.;Benstead, J.P. (Ed.). The natural history of Madagascar. Chicago, USA: The University of Chicago Press.

Sparks, J. S.,Stiassny, M. L. J. (2003)"Introduction to Madagascar's freshwater fishes" In Goodman, S.M.;Benstead, J.P. (Ed.). The natural history of Madagascar. (pp. 849-863) Chicago, USA: The University of Chicago Press.