Terrestrial Ecosystems
Vegetation
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The Seychelles hosts a high level of plant diversity on the Inner Islands, with 69 endemic plant species, including 6 endemic palm species in the Vallée de Mai on Praslin. The outer islands are coralline islands that have developed from the slow accretion of coral living in shallow waters. The coralline islands are small, flat and geologically much younger than the granitic islands. While still diverse, they do not harbor the same degree of species endemism as the granitic islands. The coral islands have 15 known floral endemic species. The island of Aldabra is the largest raised coral atoll in the world, and is considerably older than the other coralline islands and accordingly has a higher degree of endemism. Original forests on the outer islands were mainly composed of indigenous broadleaved trees such as Cordia subcordata, Calophyllum inophyllum and Guettarda speciosa.
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However, the majority of the native vegetation of the outer islands have been disturbed by human settlements activities, particularly phosphate mining, guano digging, and the building of airstrips, to create space for coconut and casuarina (Casuaurina equisetifolia ) plantations towards the end of the 19th century and these have replaced the natural vegetation in many cases. However, the demand for coconut oil declined and by the 1970’s coconut production was no longer profitable, and most plantations were abandoned. Likewise wood production from casuarina ceased with the importation of cheaper foreign wood. Scrub vegetation is also an important feature of the outer islands, and is composed of either mixed stands or, often mono-specific stands of species such as Scaevola sericea, Tournefortiaa argentea and Suriana maritima. It had however, been reported by Betts (2009) that the coastal woodland on the southern and north-eastern coast of Desroches island is largely intact. While forests have partly or wholly been restored on the Inner Islands of Seychelles restoration efforts on the outer islands are only just commencing.
Birds
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The official Seychelles Bird Records Committee lists a total of 263 species (2013), comprising of 63 breeding species, 28 annual migrants, 163 vagrants and nine extinct species (three of which were introduced) occurring in Seychelles. There are 188 confirmed records from the outer islands, 124 of which are found around the islands included in this project: Alphonse (96 species), Desroches (65 species), D'Arros (63 species), St Joseph (50 species), Farquhar (47 species), St François (47 species), and Poivre (49 species).
BirdLife International has identified 20 Important Bird Areas (IBA) in the Seychelles, nearly half of which are located around the outer islands. These include the African Banks, Aldabra Atoll, Boudeuse, Cosmoledo, D'Arros, Desneoufs, Etoile, Farquhar and Marie Louise. Birdlife International has also identified several potential marine IBAs. There are 13 endemic species of birds in Seychelles which are all globally threatened. Large numbers of Crab Plovers (max. 1,750) have been consistently recorded at St. Francois, indicating that, along with Aldabra and Cosmoledo, it may hold up to 10% of the world population of 60-80,000 during the non-breeding season. Numbers of Turnstone, Saunders’ Tern and Black-naped Tern around the same area also exceed thresholds set for the African Important Bird Area (IBA) network. |
Rare vagrant birds in Seychelles have been recorded at Desroches. The airstrip and sparser woodland have attracted and held small numbers of Amur Falcon (breeding in NE Asia, one in March 1995 being the first record for the whole of Seychelles) and Blue-cheeked Bee-eater (NE Africa to NW India) during the North West monsoon, have been spotted in recent years. Both bird species feed on insects.
In the South and Goëlletes Islands of Farquhar between 10 and 40 pairs of Black-naped Tern (Sterna Sumatrana) (protected in the Seychelles only at Aldabra) breed making it one of only 6 known breeding sites for this species in Seychelles, which hosts the entire known population of the African region.
Bijoutier and St Francois islands in the Alphonse group meet IBA criteria for four species of congregatory water-birds: Black-naped Tern, Saunders’ Tern, Crab Plover and Ruddy Turnstone. St Francois may be a site of global importance as a wintering ground for Crab Plover (Dromas ardeola); up to 1,500 birds (3% of the known world population) have been recorded. St Francois is also host to a large number and diversity of crabs, including the world largest crab Coconut or Robber Crab (Birgus latro).
In the South and Goëlletes Islands of Farquhar between 10 and 40 pairs of Black-naped Tern (Sterna Sumatrana) (protected in the Seychelles only at Aldabra) breed making it one of only 6 known breeding sites for this species in Seychelles, which hosts the entire known population of the African region.
Bijoutier and St Francois islands in the Alphonse group meet IBA criteria for four species of congregatory water-birds: Black-naped Tern, Saunders’ Tern, Crab Plover and Ruddy Turnstone. St Francois may be a site of global importance as a wintering ground for Crab Plover (Dromas ardeola); up to 1,500 birds (3% of the known world population) have been recorded. St Francois is also host to a large number and diversity of crabs, including the world largest crab Coconut or Robber Crab (Birgus latro).
Invertebrates
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The Harlequin Cockroach (Neostylopyga rhombifolia) which is widespread in the tropics is only known in Seychelles on Desroches. The millipede Dactylobius bivirgattus, a West Indian Ocean endemic, is also found in abundance in the woodlands on the lagoon side of Desroches. Impressive migration of large swarms of Wandering Glider (Pantala flavescens) and Spot-winged Glider (Pantala hymenaea), are known to occur at Alphonse Group during the NW monsoon, and also likely across the Amirantes. These species circulate throughout the Indian Ocean completing their entire life cycles en route while travelling.
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Reptiles
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The Seychelles has 3 species of terrestrial snake, of which 2 are endemic; more than 20 species of lizards, skinks and geckos and 3 species of terrapins. Aldabra has the largest surviving wild population of giant tortoises in the world (around 140,000), and the last remaining wild populations of tortoises in the Indian Ocean. Some of these giant land tortoises have also been re-introduced to Desroches, whilst Alphonse has a total population of only 11 free-roaming giant tortoises. Desroches is also the only Seychelles site for Hemidactylus brookii brookii (the Asian race of Brook’s House Gecko).
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Invasive Species
Norway (Brown) rat Rattus norvegicus is present on islands in Seychelles including Mahé, the main source of supplies and materials. Although, Ship (Black) rats are already on Desroches and Alphonse, the accidental introduction of larger, burrow-dwelling Norway Rats would add a further pressure to island species, particularly Wedge-tailed Shearwater. Alien birds, reptiles, invertebrates and plants have also had negative impacts on island ecosystems throughout Seychelles. Quarantine and contingency guidelines devised for Aride, Cousine, Cousin and North Island to minimise risk of colonisation by invasive species will be applied and refined for biosecurity on Desroches and Alphonse.
