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Ecoregion Description

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Species Richness

# of Endemic Species


584: Comoros - Mayotte

Major Habitat Type:

Oceanic Islands


Ashley Brown, Conservation Science Program, WWF-US, Washington, DC, USA


Roger Safford, BirdLife International, Cambridge, UK




The Comoros Islands are located in the Indian Ocean northwest of Madagascar in the Mozambique Channel and cover about 2,171 km2 (Mittermeier et al. 1999). From west to east, the islands include Grande Comore (Njazidja), Mohéli (Mwali), Anjouan (Ndzuani), and Mayotte (Maore), among others. Mayotte is a French territory while the other islands form the Republique Fédérale Islamique des Comores. The volcanic, mountainous Comoros Islands have a depauperate freshwater fauna that inhabits the lakes and streams of the ecoregion. 

Drainages flowing into:

Indian Ocean

Main rivers or other water bodies:

Streams originate in forested highlands, dropping precipitously to flow through the coastal plain before reaching the ocean. There is also one crater lake, Dziani Boundouni, located in the southeast portion of Mohéli Island, and two natural lakes on Mayotte: Dziani Karehani and Dziani Dzaha (crater) (Louette 1999).


On Grande Comore, the youngest and largest island, the soil is thin and rocky and there are no valleys or permanent watercourses. The 2,361 m high Karthala Volcano on Grande Comore is still active, erupting every 10 to 20 years (Henkel & Schmidt 2000).


The ecoregion experiences a tropical climate, greatly influenced by its location in the Indian Ocean. Northwest monsoon winds begin in September and the climate is hot (25- 33o C) and humid from October to April. From May to September, it is cooler and drier with southerly winds and temperatures ranging between 16 o C and 25 o C (Battistini & Vérin 1984). Rainfall varies greatly throughout the islands and by elevation, ranging from a minimum of 900 mm/year to 6,000 mm/year (FAO Inland Water Resources and Aquaculture Service Fishery Resources Division 1999), although few data exist for the wettest parts of the uplands. Periodically destructive cyclones hit the islands (Sayer et al. 1992).

Freshwater habitats:

Whereas Mohéli and Mayotte both possess streams and other water bodies, including crater lakes, the islands of Grande Comore and Anjouan possess few freshwater habitats. Mayotte, the oldest of the islands, has many meandering streams that flow from the highland rainforests of the island, in addition to the two lakes Dziani Karehani and Dziani Dzaha. On Mohéli, the freshwater, but sulphurous Dziani Boundouni, has frequent upwellings due to subterranean volcanic activity (Wetlands International 2002). 

Terrestrial Habitats:

Tropical rainforest remains in a few places at high altitudes (500 to 1,900 m asl), especially on Karthala and dry forest, mangroves, baobabs and Indo-Pacific scrub grow in parts of the lowlands (Stuart et al. 1990; Sayer et al. 1992). On lava flows, lichens, ferns, other herbaceous vegetation, and woody plants grow in succession (Henkel & Schmidt 2000). Thirty-three percent of the plant species in Comoros are endemic (Mittermeier et al. 1999). However, many plant species have been introduced to the islands. In 1979, out of 1,000 plant species identified from the Comoros, about 500 had been introduced by man (Henkel & Schmidt 2000).

Fish Fauna:

Between ten to fifteen species of fish frequent the rivers and lakes of this ecoregion. However, most of the riverine fish are not restricted to freshwater, but also inhabit the brackish deltas and ocean. The freshwater fish fauna of the Comoros is dominated by freshwater gobies and catadromous species. These species inhabit all portions of the rivers, from the forested, headwater streams to the low elevation marshes and estuaries. Species such as the rock flagtail (Kuhlia rupestris) prefer fast-flowing, clear rainforest streams such as those found on higher elevations of the islands. The catadromous and widespread Indonesian shortfin eel (Anguilla bicolor) and giant mottled eel (Anguilla marmorata) spawn at sea and move up the rivers to live as adults (Louette 1999). Sicyopterus lagocephalus is also catadromous, but is restricted to Madagascar, Reunion, Mauritius and the Comoros (FishBase 2001).

Other noteworthy aquatic biotic elements:

The ecoregion hosts sixteen freshwater snails, although all of these except those of the marine-derived Ellobiidae family are thought to have been brought to the islands by man or birds. Neritids dominate the lower watercourses on Anjouan whereas only Lymnaea natalensis and Ceratophallus sp. have been documented at elevations above 150 m (Brown 1994). 

There are over 20 species of dragonfly (Odonata) that are known from the ecoregion, especially representatives of the genera Palpopleua and Anax (Louette 1999). Several of these stream inhabitants are endemic (Samways 2003). The ecoregion also contains several species of caddisfly (Trichoptera), and the island of Anjouan has a trichoptera fauna that is similar to that of nearby continental Africa (Malicky 1989).

The freshwater Dziani Boundouni hosts a large population of little grebes (Tachybaptus ruficollis). Other birds seen at the lake are Madagascar squacco heron (Ardeola idae), striated heron (Butorides striatus of the Comoro-endemic race rhizophorae) cattle egret (Bubulcus ibis), great egret (Casmerodius albus), grey heron (Ardea cinerea), common moorhen (Gallinula chloropus), and greenshank (Tringa nebularia) (Wetlands International 2002). Several threatened wetland birds also occur on the islands: Madagascar heron (Ardea humbloti), Ardeola idae, and Madagascar harrier (Circus maillardi) (Safford 2001). The latter species has been taxonomically rearranged, and this population is now usually accepted as Madagascar serpent eagle (Circus macrosceles).

Two aquatic-dependent frogs occur on Mayotte but not the other islands: the near-endemic Mantidactylus granulatus and Boophis tephraeomystax (Louette 1999), which also occur on Madagascar and Nosy Bé islands(Glaw & Vences 1994). However, it is uncertain whether they are native and suspected that they might be accidental introductions.

Justification for delineation:

The Comoros Islands comprise this ecoregion, which hosts a diversity of brackish and freshwater fish, dragonflies, caddisflies, waterbirds, and frogs. All of the freshwater fish of the islands are from secondary families. The Miocene volcanic origin of the islands and the fact that they have never been joined with a continent explain the lack of primary fish families (Louette 1999).

Level of taxonomic exploration:

Low for fish, Medium for Odonata


Battistini, R.,Vérin, P. (1984). "Géographie des Comores" Paris, France: Agence de Co-opération Culturelle et Technique.

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

FishBase (2001) "Search FishBase" <>(2001)

Food and Agriculture, Organization (1999) "State of the World fisheries and Aquaculture 1998". Rome, Italy. FAO.

Glaw, F.,Vences, M. (1994). "A field guide to the amphibians and reptiles of Madagascar" Leverkusen, Germany: Moos-Druck.

Henkel, Friedrich-Wilhelm,Schmidt, Wolfgang (2000) Amphibians & Reptiles of Madagascar, the Mascarenes, the Seychelles & the Comoros Islands. (pp. 324) Malabar, Florida, USA: Krieger Publishing Company.

Louette, M. (1999) La faune terrestre de Mayotte, Annales du Musée Royal d’Afrique Centrale (Sciences Zoologiques), No. 284. Tervuren, Belgium: Musée Royal de l'Afrique Centrale.

Malicky, H. (1989). "Caddisflies (Insecta:Trichoptera) from the Syechelles, Comoro and Mascarene Islands" Annalen des Naturhistorischen Museums in Wien Serie B Botanik und Zoologie 93 143-160.

Mittermeier, R. A., Myers, N., et al. (1999). "Hotspots: earth’s biologically richest and most endangered terrestrial ecoregions" Mexico: CEMEX.

Safford, R. J. (2001)"The Comoros" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 185-190) Newbury and Cambridge, UK: Pisces Publications and BirdLife International (Birdlife Conservation Series No. 11).

Samways, M. J. (2003). "Threats to the tropical island dragonfly fauna (Odonata) of Mayotte, Comoro archipelago" Biodiversity and Conservation 12 1785-1792.

Sayer, J. A., Harcourt, C. S., et al. (1992) The conservation atlas of tropical forests: Africa. London, UK: IUCN.

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.

Wetlands, International (2002) "Ramsar Sites Database: A directory of wetlands of international importance" <>(2003)

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