Variation in the Distribution of Supralittoral Vegetation Around an Atoll Cay: Desroches (Amirante Islands, Seychelles)


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The shores of the small coral cay on Desroches Atoll (Amirante Islands, Seychelles) span a range of conditions from relatively sheltered (along the atoll lagoonal coast) to very exposed (facing the Indian Ocean). This appears in no way to affect the occurrence of Scaevola, which dominates the entire coastline, but the frequencies of the other characteristic but less widespread shoreline plant species (Casuarina, Cocos, Guettarda, Suriana and Heliotropium) show significant variation around the cay perimeter.


In the popular imagination, especially of people living outside the tropics, coral islands are fringed by coconut palms. In reality, except on eroding shores, the dominant species is much more likely to be the somewhat less romantic Scaevola, variously known as ‘salt bush’, ‘fan flower’, ‘Cardwell cabbage’, ‘naupaka’, ‘half-flower’ and in Seychelles ‘vouloutye’, that pan-tropically forms – or used to form – dense impenetrable thickets at and above high tide level around atoll cays as well as around various other types of island. Although Scaevola is often the dominant component, several other plants may occur with it, including of course the coconut, Cocos.

Desroches is a low linear coral-sand cay, some 5km long, 0.5-1.0km wide and 2m high, oriented south-west to north-east on the southern margin of the large (20km diameter) sunken and tilted coral atoll of the same name in the Amirantes Group, Seychelles, at 50 40-42’ S; 530, 38-41’ E (see, e.g., Baker, 1963; Stoddart & Poore, 1970). Although most of its terrestrial vegetation is no longer in its natural state, and little
evidence of its original biota remains (Stoddart & Poore, 1970) having been converted like many other Indian Ocean islands to a coconut plantation, except in the vicinity of the island’s hotel the coastal fringe does appear to be in a largely natural state (although with some probably alien components). In this it contrasts with the coastal vegetation of many of the granitic Seychelles that has been severely changed by human activity (Sauer, 1967). This study set out to document the composition of the supralittoral vegetation around Desroches as an example of an atoll cay in the Indian Ocean and to ascertain whether this vegetation was uniform or contained significant local regional variation. The Coral and Coastal Ecology of the Seychelles Research Programme is one of the three component sections of the Mitsubishi Corporation’s Global Coral Reef Conservation


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