- Astove Island
Astove Island is part of the
Aldabra Groupof the Seychelles. It is 38 km SSEof CosmoledoAtoll, located at (coord|10|06|S|47|45|E|). It is a raised coralisland of most peculiar form: a single stretch of land, more than 1 km (nearly one mile) at the widest, almost entirely encloses a shallow lagoon. This has a maximum depth of 3 metres (10 ft), and the only exit is a winding passage in the southwest, called "Gueule Bras Channel".
Astove Island measures nearly 6 km (3.7 miles) north to south and about 4 km (2.5 mi) at most east to west. The land area is 4.96 km²Verify source|date=April 2008 , and the total area including the
lagoon9.5 km²Verify source|date=April 2008 . The only settlement, on the western coast, has been abandoned since the 1980s. There is a grass airstripon the north east point of the island, and remnants of a former coconutand sisal plantation. Today, the island is rarely visited - usually by scientistsresearching the lagoon's ecology- but the near-vertical drop-off from its outer reefedge is a popular location for divingcruises.
Geology and geography
Astove's unusual structure has raised questions about its formation. It was suggested that Astove is not a true raised
atoll, but rather a reefflat, with the lagoon being washed out later. In any case, the lagoon indeed grows slowly, owing to rainwater, acidic from the soil's humic acids, dissolving the lagoon's carbonate rockbottom. This causes the unusual milky-white color of the lagoon's waters.Piggott (1961)]
On the large land mass towards the western tip, exposed reef rock raises to some 5 m (15 ft) ASL. Elsewhere it is largely covered by
gravelly debris. Dunes of up to 18 m (60 ft) line the windswept eastern rim of the island, and the eastern part of the lagoon is especially shallow due to the inblown dune sand. Astove Island's fringing reefis just about 180 m (300 ft) wide. As noted above, beyond the reef's outer edge the seafloor drops down steeply, with a depth of 550 m (300 fathoms) a mere 300 metres (900 ft) away from the shoreline.
climateis dominated by the southeast trade winds which are most pronounced between April and November. Temperatures are around 28 °C (83°F) in the shade during that time, and slightly higher during the northwest monsoonseason. At that time, tropical cyclones with torrential rain sometimes hit the island, but overall it is very arid.
Astove Island has a very thin
soillayer overlying its rocky core, which is pockmarked with caverns. Guanoof nesting seabirds has accumulated in these, and the western part has been worked over and some of the guano was mined in the past. Large stretches of the reef rock were stripped bare of vegetation, but some " Pisonia grandis" and White Milkwood(" Sideroxylon inerme") persisted. The general vegetation on much of the island's western side is herbaceous plants however, mainly the leadwort " Plumbago aphylla", as well as " Stachytarpheta" speciesand the crowfoot grass" Dactyloctenium pilosum". Coconut Palms ("Cocos nucifera") remaining from the struggling plantation along the western shore, Sisal("Agave sisalana"), and wild cottonplant("Gossypium") are also found here and there. Maize("Zea mays") was planted by the guano miners, but presumably this plant which depends on constant care has disappeared since.
The eastern dunes are overgrown with the
dropseed grass" Sporobolus virginicus" near the sea, and on the higher parts " bwa matlo" ( Bay Cedar, " Suriana maritima") shrubs are found. In more sheltered places, a regular scrubland of " vouloutye" (" Scaevola sericea") and Velvet Soldierbush("Tournefortia argentea"), with some "Pisonia", occurs. Here, the main herbs are fimbries ("Fimbristylis") and the parasitic vine" Cassytha filiformis".
The flats around the lagoon show a mixture of grassland (mainly
Pembagrass, " Stenotaphrum dimidiatum") and " Pemphis acidula" scrub; in places, it is difficult to penetrate to the lagoon through the mass of "Pemphis" and "bwa matlo". Small Grey Mangroves ("Avicennia marina") line much of the southern half of the lagoon rim.
Astove Island is home to four landbirds:
Abbott's Sunbird("Cinnyris sovimanga buchenorum" or "C. abbotti buchenorum") - only occurs here and on nearby Cosmoledo
Madagascar Cisticola("Cisticola cherina")
Pied Crow("Corvus albus")
Madagascar White-eye("Zosterops maderaspatanus maderaspatanus")
There are few seabirds, probably due to the presence of
rats and feral pigs, left behind when the settlement was abandoned. Unlike the other two atolls of the group, ( Aldabraand Cosmoledo), there are no predator-free islets except for a few small sandbanks close to the lagoon entrance. At the lagoon, Caspian Terns ("Hydroprogne caspia") will often be seen but it is not known whether or not they ever breed on the sandbanks. Indopacific Sooty Terns ("Onychoprion fuscatus nubilosus") and Western Black-naped Terns ("Sterna sumatrana mathewsi") have also been reported. Green Turtles ("Chelonia mydas") remain very common here despite years of exploitation and remarkably high numbers will be seen on dives or from tender trips to the lagoon entrance close to high tide.
* (1961): Notes on some of the Seychelles Islands, Indian Ocean. "Atoll Research Bulletin" 83: 1-10. [http://www.botany.hawaii.edu/faculty/duffy/ARB/076-84/83.pdf PDF fulltext]
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