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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

586: Mascarenes

Major Habitat Type:

Oceanic Islands

Author:

Robin. Abell and Ashley Brown, Conservation Science Program, WWF-US, Washington, DC, USA

Reviewers:

Roger Safford, BirdLife International, Cambridge, UK

Countries:

Mauritius; Reunion

Boundaries:

The isolated islands of the Mascarenes ecoregion host a highly endemic aquatic biota, including several gobies that inhabit swift streams. The islands are of volcanic origin and are situated in a line along a mid-Ocean ridge, located east of Madagascar in the western Indian Ocean. The largest islands are the French Dependent Territory (Département) of Réunion (2,500 km2) and the island of Mauritius (1,900 km2). Mauritius, along with Rodrigues (110 km2) and several smaller islands, form the single independent nation of Mauritius. Réunion, at about 690 km from Madagascar, is the most westerly of the islands, followed by Mauritius; Rodrigues lies some 570 km further to the east. 

Drainages flowing into:

Indian Ocean

Main rivers or other water bodies:

On the island of Mauritius, the Grand River South East (34 km) is the longest river, followed by Rivière du Poste (23 km), Grand River North West (22 km), Rivière La Chaux (22 km), and Rivière des Créoles (20 km). In addition to numerous man-made reservoirs, Mauritius has two natural crater lakes, Grand Bassin and Bassin Blanc (Government of Mauritius 2001). Rodrigues and Réunion are similarly endowed with high-gradient rivers.

Topography:

The islands have a rugged topography with many ravines and cliffs. On Réunion, Piton de la Fournaise (2,525 m) becomes active several times each year, and as a result the island’s topography is particularly steep. The other major peak on Réunion is Piton des Neiges, a long extinct volcano that reaches 3,069 m and is the highest peak in the Indian Ocean (Defos du Rau 1960). On the island of Mauritius, the highest point is Piton de la Rivière Noire, which reaches a height of only 828 m. Mauritius is considered to be the oldest of the Mascarene Islands and was formed by three periods of volcanic activity occurring between 10 million and 20,000 years ago (Montaggioni & Nativel 1988). The island consists of an irregular central plateau at about 300-600 m, surrounded by three mountain ranges and plains (Ramdin 1969). Rodrigues has even lower relief, with rolling hills rising only to 390 m. Though comprised primarily of basaltic lava and some volcanic dust, there are small areas in the south and the east of Rodrigues where wind-blown sand has accumulated to form limestone rocks. In these areas caves have formed (Sok Appadu & Nayamuth 1999). Many smaller islands also occur in this ecoregion; of particular interest is Round Island, a small island off the northern tip of Mauritius with a distinctive flora and fauna (especially reptiles) comprising many species found nowhere else.

Climate:

At lower elevations, summer (December-April) temperatures average 30° C, whereas in winter (May-November) the average is closer to 25° C. However, at the highest elevations the temperature averages only 18° C and ice sometimes forms. Southeasterly trade winds blow throughout the year. On Mauritius, rainfall varies from 890 mm in coastal areas on the leeward side of the island, to 4,445 mm in parts of the central plateau, with large variations over short distances. Due to this rainfall pattern, both tropical moist and tropical dry forests grow on Mauritius. Abundant and heavy rains from cyclones cause pronounced erosion and landslides (WWF and IUCN 1994). The climate on Réunion is influenced by southeasterly trade winds and depressions. Mean annual temperatures are less than 16° C over large areas, and up to 25° C in the drier, leeward lowlands (Le Corre & Safford 2001). Rainfall ranges from less than 2,000 on the leeward side of the island, to 5,000 mm (and up to 9,000 mm locally) in the mountains. On Rodrigues, annual rainfall varies between 1,000 and 1,700 mm, and temperatures are roughly 24° C (Safford 2001).

Freshwater habitats:

Fast-flowing rivers and streams are relatively abundant on the Mascarene Islands. Several of these rivers are marked by waterfalls, the highest being Tamarin Falls or Sept Cascades (293 m). Mangroves occur along the coast near river mouths and estuaries. On Mauritius, small areas of mangrove are present at various locations including Terre Rouge, Riviere Noire, Baie du Cap, Riviere du Rempart, Trou d’Eau Douce, Poste Lafayette, Bras d’Eau, Roches Noires, and Poudre d’Or (Institute of Marine Sciences et al. 1998).

Terrestrial Habitats:

The main communities of native vegetation on the islands historically were probably lower montane wet evergreen forest, scrub and marsh vegetation in the uplands, evergreen or semi-deciduous forest in the rain-shadow and palm savanna at lower elevations (Le Corre & Safford 2001). Habitats ranged from coastal wetlands and swamp forests at low elevations, through lowland dry forest, rain forest, and palm savanna, to montane deciduous forests and finally (on Réunion) to heathland vegetation types on the highest mountains. Most of the original vegetation has been destroyed and almost all remaining native plant communities have been badly degraded by introduced species (Stuart et al. 1990; WWF and IUCN 1994). Major plant families include Sapotaceae, Ebenaceae, Rubiaceae, Myrtaceae, Clusiaceae, Lauraceae, Burseraceae, Euphorbiaceae, Sterculiaceae, Pittosporaceae, and Celastraceae. There is a high diversity of palm species on the islands, including many endemic genera (WWF and IUCN 1994).

Fish Fauna:

About thirty-five species of fish use Mascarene freshwater habitats, and many move between fresh, brackish, and marine waters. Gobies dominate the freshwater fish fauna. Other fish families with freshwater species represented in this ecoregion include Anguillidae, Kuhliidae, and Eleotridae. According to Fishbase (2001), Réunion has the highest number of native fish species (30), followed by Mauritius (21), and the two islands have many species in common. Rodrigues has a depauperate freshwater fish fauna (4 species).

Description of endemic fishes:

About twenty species of fish are tied to freshwater habitats for part of their life cycle and were included in our richness estimates. Of these, five are endemic to the Mascarenes (Hypseleotris cyprinoides, Cotylopus acutipinnis, Glossogobius kokius, Gobius commersonii, and Oxyurichthys guibei). Cotylopus acutipinnis, a goby endemic to Réunion, hatches in the sea and following its larval stage migrates to swift rainforest streams to live as an adult (FishBase 2001). Sicyopterus lagocephalus, a goby found predominantly in the Mascarenes, has a similar life history. 

Other noteworthy aquatic biotic elements:

About 20 species of snail are known from the fresh and brackish waters of the Mascarenes. The fauna is a mixture of those with Afrotropical (e.g., Afrogyrus rodriguezensis and Bulinus cernicus) and Asiatic (e.g., Lymnaea mauritania and Gyraulus mauritianus) affinities and at least two are known to have been introduced by man. The endemic Lantzia carinata lives in or near a waterfall on the island of Réunion and is apparently adapted to cling to rocks (Brown 1994). This species was recently rediscovered after more than a century.

Two species of dragonfly, Argiocnemis solitaria and Platycnemis mauriciana, are currently considered endemic to Mauritius and critically endangered (IUCN 2002). However, both species are known only from the type locality, and thus, require taxonomic verification. The specific status of P. mauriciana is particularly in doubt (Samways 2002). 

Until the arrival of man, the islands supported several endemic (and often extraordinary) aquatic birds (Cheke 1987), but these are all extinct. The only surviving native freshwater bird species are green-backed heron (Butorides striatus), on all three main islands, and common moorhen (Gallinula chloropus) on Mauritius and Réunion.

Justification for delineation:

The Mascarene Islands define the boundaries of this ecoregion, which supports an endemic freshwater fauna that shares affinities with Madagascar, East Africa, and Asia. All of the endemic fish species are from the marine family, Gobiidae.

Level of taxonomic exploration:

Poor

References/sources:

Brown, David (1994). "Freshwater snails of Africa and their medical importance" London, UK: Taylor & Francis.

Cheke, A. S. (1987)"An ecological history of the Mascarene Islands, with particular reference to extinctions and introductions of land vertebrates" In Diamond, A.W. (Ed.). Studies of Mascarene Island birds. (pp. 5-89) Cambridge, UK: Cambridge University Press.

Defos du Rau, J. (1960). "L’Ile de la Réunion" Bordeaux, France: Institut de Géographie.

FishBase (2001) "Search FishBase" <http://www.fishbase.org/search.cfm>(2001)

Government of, Mauritius (2001) "Official web portal: geography and climate" <http://ncb.intnet.mu/govt/geograph.htm.>(2001)

Institute of Marine, Sciences, Fao, et al. (1998). "Overview of land-based sources and activities affecting the marine, coastal and associated freshwater environment in the eastern African region. UNEP Regional Seas Reports and Studies No. 167" Dar es Salaam, Tanzania: UNEP.

IUCN, W. W. F. and (1994). "Centres of plant diversity: A guide and strategy for their conservation. 3 Volumes" Cambridge, UK: IUCN Publications Unit.

Le Corre, M.,Safford, R. J. (2001)"La Réunion and Iles Eparses" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 693-702) Newbury and Cambridge, UK: Pisces Publications and BirdLife International (Birdlife Conservation Series No. 11).

Montaggioni, L.,Nativel, P. (1988). "La Réunion, Ile Maurice, géologie et aperçus biologiques" Paris, France: Masson.

Ramdin, T. (1969). "Mauritius, a geographical survey" London, UK: University Tutorial Press.

Safford, R. J. (2001)"Mayotte" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 597-601) Newbury and Cambridge, UK: Pisces Publications and BirdLife International (Birdlife Conservation Series No. 11).

Samways, M. J. (2002). "Threatened Odonata species of Africa" Odonataologica 31(2) 151-170.

Sok Appadu, S. N.,Nayamuth, A. R. (1999) "Initial National Communication of the Republic of Mauritius under the United Nations Framework Convention on Climate Change" <http://www.unfccc.de/resource/docs/natc/maunc1/>(2001)

Stuart, S. N., Adams, R. J., et al. (1990) Biodiversity in Sub-Saharan Africa and its islands: Conservation, management and sustainable use, Occasional Papers of the IUCN Species Survival Commission No. 6. Gland, Switzerland: IUCN.

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