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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

587: S. Tome & Principe - Annobon

Major Habitat Type:

tropical and subtropical coastal rivers

Author:

Ashley Brown and Robin Abell, World Wildlife Fund-US, Washington, DC, USA

Reviewers:

Angus Gascoigne, Environmental Information and Technical Services, São Tomé, São Tomé et Príncipe

Countries:

Equatorial Guinea; Sao Tome and Principe

Boundaries:

Located off the coast of Equatorial Guinea and Gabon, these volcanic islands include São Tomé (836 km2), Príncipe (128 km2), and Annobón (17 km2), as well as several smaller islands. Most of this ecoregion lies within the Democratic Republic of São Tomé and Príncipe. Annobón is part of Equatorial Guinea and lies 180 km southwest of São Tomé.

Drainages flowing into:

Gulf of Guinea, Atlantic Ocean

Main rivers or other water bodies:

Rivers drain from the central highlands of São Tomé and the other islands, radiating towards the coasts. The largest river of São Tomé is the Io Grande, which drains the southeastern portion of the island. Other large rivers on São Tomé include the Abade, the Manuel Jorge and the Rio d\'Ouro and the Rio Papagaio is the longest river on Príncipe (Juste & Fa 1994).

Topography:

The islands are generally mountainous in the interior, sloping sharply down to the coasts. In São Tomé, one major mountain chain runs north to south while a second runs northwest to southwest. Príncipe has two chains as well, both running east to west (Juste & Fa 1994). The highest peak on São Tomé is 2,024 m asl and on Príncipe it is 948 m asl. On the much smaller island of Annobón the highest peak is 630 m asl (Juste & Fa 1994). 

Climate:

The islands have an oceanic equatorial climate with temperatures about 22 o C to 33 o C near sea level. At higher altitudes, the temperature often drops to 9 o C or lower (Sayer et al. 1992; Juste & Fa 1994). Annual rainfall varies dramatically depending on elevation. The maximum annual rainfall is 7,000 mm on São Tomé, 5,000 mm on Príncipe, and 3,000 mm on Annobón. The main dry season on São Tomé and Príncipe occurs from June to September and is called the gravana. A smaller dry season called the gravanito lasts from December to February. The seasons on São Tomé and Príncipe are more affected by the inter-tropical front than are the seasons on Annobón. On Annobón, oceanic winds cause a well-defined single dry season that lasts from May to October (Juste & Fa 1994).

Freshwater habitats:

On each of this ecoregion’s islands, swift rivers marked by waterfalls and rapids descend from highland interiors and flow to the Gulf of Guinea. Most rivers are perennial and experience seasonal fluctuations. The islands of São Tomé and Annobón also have volcanic crater lakes.

Terrestrial Habitats:

Prior to conversion, the primary vegetation of the ecoregion was tropical rainforest (Juste & Fa 1994). Now much of the land is used for agrarian purposes. The remaining primary and secondary forests fall under the category of lowland forest, montane rainforest, mossy forest, and mangrove forest. The forests on São Tomé, Príncipe and Annobón contain many endemic and imperiled species such as Rinorea thomensis, Afrocarpus mannii, Craterispermum montanum, and Pandanus thomensis (WCMC 2001).

Fish Fauna:

There are only two species of freshwater fish: the frillfin goby (Bathygobiussoporator) and the West African freshwater goby, Awaous lateristriga (FishBase 2001). The widespread and brackish banded lampeye, Aplocheilichthys spilauchena, is found up to an altitude of 50 m in the Rio Papagaio on Príncipe (Rossignon 1999). All species are able to tolerate brackish water. 

Other noteworthy aquatic biotic elements:

Overall, freshwater faunal richness is extremely low, but there is high endemism among certain taxa. For instance, only five species of frogs live in this ecoregion, but all are endemic. Leptopelis palmatus lives in the lowland forests of only Príncipe, and is distinct enough from the mainland L. rufus that it is considered a different species and a classic example of island gigantism. Nesionixalus thomensis and Ptychadena newtoni have only been found on São Tomé. N. molleri and Phrynobatrachus dispar live on both São Tomé and Príncipe (Schiøtz 1999; Christy 2001). The genus Nesionixalus is endemic to the two islands.

Only three species of freshwater molluscs live in the ecoregion, two from the Neritidae family and the vector of schistosomiasis, Bulinus forskalii. This species shows distinctive morphological characteristics in comparison with mainland forms (Brown 1991). Like gobiid fish, Neritidae species are primarily marine but some lineages have adapted to live in brackish and fresh water. The freshwater crab, Potamonautes margaritarius, is endemic to São Tomé (Cumberlidge 1999). Four species of freshwater shrimp have been recorded from the islands, Macrobrachium zariquieyi, M. chevalieri, Atya intermedia,and Atya sulcatipes (Holthuis 1966).

On São Tomé, Lagoa Amelia located in the center of the island at 1,400 meters is covered by a floating two meter thick layer of vegetation comprised of mosses, ferns and orchids including the endemic Diaphananthe brevifolia. The crater walls are home to the endemic giant begonia Begonia crateris. On Annobón, Lagoa A Pot is located in the north of the island and consists of open water populated with the shrimp species A. sulcatipes and the fish Gambusia affinis introduced by the Spanish to control mosquito larvae in the colonial period. The depths of the two crater lakes are unknown.

Justification for delineation:

São Tomé, Príncipe, Annobón form the boundaries of this ecoregion. These islands were formed by volcanic eruptions that occurred along a fracture in the earth’s crust during the lower Tertiary and early Quaternary (Juste & Fa 1994). Because the islands have never been connected with each other or the mainland, which is about 220 km away from São Tomé and Príncipe and 340 km from Annobón, the flora and fauna are relatively low in richness but high in endemism (Jones 1994). Bioko, the largest island in the Gulf of Guinea, is part of the volcanic chain that includes Mt. Cameroon, São Tomé, Príncipe, and Annobón. However, Bioko is included in the Northern Gulf of Guinea Drainages - Bioko ecoregion [518] because the island was connected to the continent some 10-12,000 years ago and shares a majority of its fish species with those of the mainland (Kamdem Toham, pers. comm., 2000).

Level of taxonomic exploration:

Fair. The crater lakes on São Tomé and Annobón are unique habitats that offer unique opportunities for palaeobotanical and palaeoclimatological research. Gascoigne (1993; 1996) provides a bibliography on the fauna of the islands.

References/sources:

Brown, D. S. (1991). "Freshwater snails of São Tomé, with special reference to Bulinus forskalii (Ehrenberg), host of Schistosoma intercalatum" Hydrobiologia 209 141-153.

Christy, P. (2001)"São Tomé and Príncipe" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 727-731) Newbury and Cambridge, UK: Pisces Publications and BirdLife International (Birdlife Conservation Series No. 11).

Cumberlidge, Neil (1999). "The freshwater crabs of West Africa: Family Potamonautidae" Paris, France: IRD.

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

Gascoigne, A. (1993). "A bibliography of the fauna of the islands of São Tomé e Príncipe and the island of Annobon (Gulf of Guinea)" Arquipelago Ciencias Da Natureza 11 91-105.

Holthuis, L. B. (1966). "The R/V Pillsbry deep-sea biological expedition to the Gulf of Guinea, 1964-65. 11. The freshwater shrimps of the island of Annobon, West Africa" Studies in Tropical Oceanography 4(1) 224-239.

Jones, P. J. (1994). "Biodiversity in the Gulf of Guinea: An overview" Biodiversity and Conservation 3(9) 772-784.

Juste, B. J.,Fa, J. E. (1994). "Biodiversity conservation in the Gulf of Guinea Islands: Taking stock and preparing action (Jersey Wildlife Preservation Trust, Jersey, June 4-6, 1993)" Biodiversity and Conservation 3(9) 759-771.

Rossignon, O. (1999) "Contribution à l'ecologie des crevettes dulcaquicoles de São Tomé: du cadre limnologique à l'elevage". Faculté Universitaire des Sciences Agronomiques de Gembloux.

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

Schiøtz, A. (1999) Tree frogs of Africa. Frankfurt, Germany: Edition Chimaira.

Wcmc (2001) "Vallée de Mai Nature Reserve" <http://www.wcmc.org.uk/protected_areas/data/wh/mai.html>(2001)

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