Aldabra

"The principal difference between Aldabra and other 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 s, which attain a height of 10 feet and a diameter of a foot or more."

"The vertebrate assemblage of Aldabra Atoll has been comparatively well studied. Three 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 , three , , , , and , 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."

"Documenting post- trajectories of coral reef communities is crucial to understand their resilience to . 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 and ', 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."

"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 ' (Forsk.) Vierh., ' (L.) Lam., ' (Perr.) C.B. Rob., and ' Lam. In a few localities only, these are accompanied by one or other of ' Willd., ' Sm., or ' Koen. The fern ' 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 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."

"A very large endemic population of , which are the major terrestrial herbivores, survives on the western 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 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."