Mascarene Islands
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The Mascarene Islands (or Mascarenhas Archipelago) is a group of islands in the Indian Ocean east of Madagascar, which includes Mauritius, Réunion, Rodrigues, and Cargados Carajos shoals. The collective title is derived from the Portuguese navigator Pedro Mascarenhas, who first visited them in 1512. The islands share a common geologic origin, and form a distinct ecoregion with a unique flora and fauna.
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Geology
The Mascarene Islands are volcanic in origin, and were created as the African plate drifted over the Réunion hotspot. Mauritius is the oldest of the existing islands, and was created 8-10 million years ago (MYA), along with Rodrigues ridge, and undersea ridge. The islands of Rodrigues and Réunion were created in the last two million years. Réunion is the largest of the islands (2,500 km²), followed by Mauritius (1,900 km²) and Rodrigues (110 km²). Réunion is home to the highest peaks in the Mascarenes, the shield volcanoes Piton des Neiges (3,069 m) and Piton de la Fournaise (2,525 m). Piton de la Fournaise, on the southeastern corner of Réunion, is one of the most active volcanoes in the world, erupting last on August 13, 2004. Piton de la Rivière Noire (828 m) is the highest peak on Mauritius, and the gentle hills of Rodrigues rise to only 390 m.
The Mascarene Plateau is an undersea plateau that extends approximately 2000 km, from the Seychelles to Réunion. The plateau covers an area of over 115,000 km² of shallow water, with depths ranging from 8 to 150 meters, plunging to 4000 m to the abyssal plain at its edges.
The northern part of the plateau, including the Seychelles, is formed of granite, and is a fragment of the ancient supercontinent of Gondwana. the southern part of the plateau, including the Saya de Malha Bank, Nazareth Bank, and Cargados Carajos Shoals (Saint Brandon), were formed by the Reunion hotspot. These were once volcanic islands much like Mauritius and Réunion, which have now sunk or eroded to below sea level, or, in the case of the Cargados Carajos, to low coral islands. The Saya de Malha Bank formed 35 million years ago, and the Nazareth Bank and the Cargados Carajos shoals after that. Limestone banks found on the plateau are the remnants of coral reefs, indicating that the plateau was a succession of islands. Some of the banks may have been islands as recently as 18,000 - 6,000 years ago, when sea levels were up to 130 meters lower during the most recent ice age.
Macarene forests
The Mascarene islands form a distinct ecoregion, known as the Mascarene forests. The islands were formerly covered in tropical moist broadleaf forest, and harbored a diverse range of forest types. Near the seacoast were coastal wetlands and swamp forests, transitioning to rain forest to windward and lowland dry forest to leeward, palm savannas, montane deciduous forests, and montane heathlands on the highest peaks of Réunion.
The islands are home to many endemic plants and animals. Most of the Mascarene flora and fauna is thought to be derived originally from Madagascar and Africa. The islands were never connected to the mainland, so the flora and fauna of the Mascarenes arrived from over the sea. Prehistoric islands of the Mascarene Plateau, now disappeared under the sea, may have served as 'stepping stones' which allowed species to island-hop from the Seychelles or Madagascar. The Mascarenes are home to one endemic family of flowering plants, Psiloxylaceae, which has only one species, Psiloxylon mauritanum.
The islands have no native mammals, except for bats. Many of the Mascarene birds evolved into flightless forms; the most famous of which was the Dodo, an extinct flightless pigeon of Mauritius. 16 endemic bird species survive on the islands. Mauritius, Réunion, and Rodrigues were also each home to one or more species of giant tortoise (Geochelone spp.). There are 13 living endemic reptile species, including a number of species of day geckoes (genus Phelsuma).
Many of the native Mascarenes flora and fauna has become endangered or extinct since the human settlement of the islands in the 17th century. Settlers cleared most of the forests for agriculture and grazing, and introduced many exotic species, including pigs, rats, cats, monkeys, and mongooses. Fourteen bird species became extinct; in addition to the Dodo, some of the other extinct species are the Rodrigues Solitaire, a flightless pigeon related to the Dodo, and the Réunion Flightless Ibis. The giant tortoises are also extinct.
The Tambalacoque (Sideroxylon grandiflorum), often called the dodo tree, is also threatened with extinction. It depended on the Dodo for reproduction, as its seeds can only germinate after passing through the digestive tract of a Dodo, which removes the seeds' thick outer coating. Scientists are using turkeys to process the seeds in an effort to save the tree.
Reference
- Quammen, David, (1996) The Song of the Dodo. Touchstone, New York.
- Diamond, Jared, (1984) "Historic extinctions: A rosetta stone for understanding prehistoric extinctions". In: P. Martin and R. Klein (eds.) (1984) Quaternary Extinctions: A prehistoric revolution. University of Arizona Press, Tucson.
External link
- Mascarene forests (World Wildlife Fund) (http://www.worldwildlife.org/wildworld/profiles/terrestrial/at/at0120_full.html)
- Dispersal of the Genus Phelsuma in the Mascarenes (Phelsumania) (http://www.phelsumania.com/public/articles/biogeography_dispersal_mascarenes.html)de:Maskarenen