Aldabra

Aldabra is an atoll, consisting of four main limestone islands which form a rim around a large, shallow lagoon. Aldabra is in the western Indian Ocean, approximately 1040 km south of the equator and 650 km east of the African mainland. The atoll’s maximum length is about 30.5 km with a maximum width about 13 km. The largest of the four main islands is famous for its large number of Aldabra giant tortoise giant tortoises. There are about 40 small islands and rocky outcrops inside the lagoon. The atoll is part of the Aldabra Group of islands belonging to the Outer Islands (Seychelles) Outer Islands of the Republic of Seychelles. In 1982 Aldabra was declared a World Heritage Site UNESCO World Heritage Site. Quotes The principal difference between Aldabra and other coral islands is that it seems to be of very ancient formation and has undergone an elevation of 15 to 20 feet. The island is flat, composed almost entirely of naked coral rock, rough and jagged, completely honeycombed in every direction with pits and fissures. Scarcely any soil exists, excepting where a small quantity of rich mold, formed by decomposing coral, has accumulated in hollows of the rock. The sea face is an overhanging cliff of rock, but in a few places, especially on Île Picard and on the west coast, are sandy beaches and low sand-hills. Upon the south coast are Dune Jean Louis and Dune du Mêche, sand hills, which reach 65 feet above sea level—the highest points in Aldabra.Nearly the whole surface is covered with a dense, almost impenetrable scrub of tangled bushes. No large trees now exist except the mangroves, which attain a height of 10 feet and a diameter of a foot or more. William Louis Abbott, Notes on the natural history of Aldabra, Assumption and Glorioso islands, Indian Ocean Proceedings of the United States National Museum 1894 XVI 973 759–764 https://repository.si.edu/bitstream/handle/10088/13354/1/USNMP-16_973_1894.pdf (quote from p. 760) The Pleistocene Pleistocene vertebrate assemblage of Aldabra Atoll has been comparatively well studied. Three Late Pleistocene Upper Pleistocene fossil localities have been described yielding birds, reptiles and terrestrial molluscs. Those of Bassin Cabri and Bassin Lebine on Île Picard are undated but must be in excess of 136,000 YBP, whereas Point Hodoul on Malabar Island is circa 100,000 YBP. Aldabra was seemingly completely submerged between deposition of the Île Picard and Point Hodoul deposits, resulting in local faunal extinctions. Here we present the results of an ongoing study of fossil material collected on Île Picard in 1987, which reveals a more diverse assemblage than previously realised. Notable discoveries are an Pond heron Ardeola heron, three Procellariformes, Tropicbird tropic-bird Phaethon, Larus gull Larus, Dryolimnas rail Dryolimnas, Circus (bird) harrier Circus and Tyto owl Tyto, plus evidence of recolonisation of the atoll by some seabirds, rail, harrier, owl, giant tortoises and lizards after the Île Picard/Point Hodoul submergence event. Julian P. Hume, David Martill, and Richard Hing, A terrestrial vertebrate palaeontological review of Aldabra Atoll, Aldabra Group, Seychelles PLOS One March 28, 2018 https://doi.org/10.1371/journal.pone.0192675 10.1371/journal.pone.0192675 13, 3 e0192675 Documenting post-Coral bleaching bleaching trajectories of coral reef communities is crucial to understand their resilience to climate change. We investigated reef community changes following the 2015/16 bleaching event at Aldabra Atoll, where direct human impact is minimal. We combined benthic data collected pre- (2014) and post-bleaching (2016–2019) at 12 sites across three locations (lagoon, 2 m depth; seaward west and east, 5 and 15 m depth) with water temperature measurements. While seaward reefs experienced relative hard coral reductions of 51–62%, lagoonal coral loss was lower (− 34%), probably due to three-fold higher daily water temperature variability there. Between 2016 and 2019, hard coral cover did not change on deep reefs which remained dominated by turf algae and Halimeda, but absolute cover on shallow reefs increased annually by 1.3% (east), 2.3% (west) and 3.0% (lagoon), reaching, respectively, 54%, 68% and 93% of the pre-bleaching cover in 2019. Full recovery at the shallow seaward locations may take at least five more years, but remains uncertain for the deeper reefs. The expected increase in frequency and severity of coral bleaching events is likely to make even rapid recovery as observed in Aldabra’s lagoon too slow to prevent long-term reef degradation, even at remote sites. Anna Koester, Valentina Migani, Nancy Bunbury, Amanda Ford, Cheryl Sanchez, and Christian Wild, Early trajectories of benthic coral reef communities following the 2015/16 coral bleaching event at remote Aldabra Atoll, Seychelles Scientific Reports 10 1 2020 17034 https://www.nature.com/articles/s41598-020-74077-x 10.1038/s41598-020-74077-x Mangrove trees grow only on sheltered coasts, hence on Aldabra they occur along the shores of the lagoon. In these mangrove communities four species are common and were found in each locality visited. These are Avicennia marina (Forsk.) Vierh., Bruguiera gymnorhiza (L.) Lam., Ceriops tagal (Perr.) C.B. Rob., and Rhizophora mucronata Lam. In a few localities only, these are accompanied by one or other of Lumnitzera racemosa Willd., Sonneratia alba Sm., or Xylocarpus granatum Koen. The fern Acrostichum aureum L. is abundant on Aldabra, sometimes in association with mangroves but more commonly among the maritime scrub where it tends to occur in crevices and Sinkhole#Solution sinkholes solution holes at a slightly lower level than the trees and shrubs of the scrub. Mangroves occur almost all round the lagoon shores, more commonly in some places than in others, more luxuriantly in some places than in others. Along only a few rocky stretches of the lagoon shores are they absent. William Macnae, Mangroves on Aldabra Philosophical Transactions of the Royal Society of London. B, Biological Sciences 260 836 4 March 971 237-247 https://royalsocietypublishing.org/doi/abs/10.1098/rstb.1971.0013 10.1098/rstb.1971.0013 A very large endemic population of Aldabra giant tortoise giant land tortoises, which are the major terrestrial herbivores, survives on the western Indian Ocean atoll of Aldabra. Tortoise densities are highest in the inland areas of the south-east where the habitat is being greatly modified by tortoise activity. In particular, they are responsible for considerable soil erosion and the death of many trees and shrubs with the resultant reduction in the amount of shade cover, which is so important to tortoise survival. There are also signs that food resources may be limiting: the low vegetation is intensively cropped; there are pronounced browse lines on most tree species and tortoise growth rates are reduced. A reduction in tortoise numbers is therefore a distinct possibility. L. F. H. Merton, D. M. Bourn, and R. J. Hnatiuk, Giant tortoise and vegetation interactions on Aldabra Atoll—Part 1: Inland Biological Conservation 9 4 1976 293-304 https://www.sciencedirect.com/science/article/abs/pii/0006320776900513 10.1016/0006-3207(76)90051-3 External links One of the most isolated ecoregions in the World , ALDABRA: Seychelles: Amazing Planet (4K) 2023 March 26, 2023 YouTube https://www.youtube.com/watch?v=wOvcpZzyK6U Guardians of Aldabra August 16, 2023 DocumentAria film, YouTube https://www.youtube.com/watch?v=Buf84bapmz0 Discovering the Pristine Beauty of Aldabra Atoll, Seychelles December 22, 2024 World Wonders, YouTube https://www.youtube.com/watch?v=lJBkLOoynsk Category:Islands of Africa Category:Seychelles