Rhachistia aldabrae 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Mollusca Gastropoda Stylommatophora Cerastidae

Scientific Name: Rhachistia aldabrae (Martens, 1898)
Common Name(s):
English Aldabra Banded Snail

Assessment Information [top]

Red List Category & Criteria: Extinct ver 3.1
Year Published: 2009
Date Assessed: 2006-01-11
Needs updating
Assessor(s): Gerlach, J.
Reviewer(s): Pollock, C.M., Miller, R.M. & Seddon, M.B.
This snail was locally abundant in the 1970s and, a rapid decline and difficulty finding individuals starting in the 1980s notwithstanding, was still represented by shells in 2000. However, despite extensive and repeated searches in all previously recorded and potentially inhabitable areas, no evidence of its continued survival has been found since then. The last live individual was seen in 1997. Rangers have been looking out for the species since 2006. It has been concluded that this species is extinct as a result of climate change (Gerlach 2007). Increasing frequency of dry years is believed to have led to neonatal mortality and complete recruitment failure, causing population senescence and extinction shortly after 1997.

Geographic Range [top]

Range Description:Endemic to Aldabra atoll, in the Seychelles islands, this species' area of occupancy (AOO) was estimated to be 150 km2.
Countries occurrence:
Regionally extinct:
Seychelles (Aldabra)
Additional data:
Estimated area of occupancy (AOO) - km2:150
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:This snail was locally abundant in the 1970s, though it was believed to have declined since then; the only change in this time was an increase in dry years. Its shells were found as recently as 2000. However, despite extensive searches, no evidence of its continued survival has been found since.
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:An arboreal species that was found on trees in open woodland, in the prolonged dry season this snail aestivated (remains in a dormant state) on trees.

Threats [top]

Major Threat(s): This species was restricted to Aldabra atoll (area of occupancy estimated to be 150 km2), all of which is less than 8 m above sea level and mostly 1-2 m above sea level. Sea level rise was therefore a major threat throughout its range. A small number of rat-eaten shells have been found, indicating that low levels of rat predation were a minor threat. In the 1970s, the species was common and widespread, but declined rapidly thereafter. Only isolated individuals were found in the 1980s and the last one in 1997. An increase in the frequency of relatively dry years has been linked to this species' decline: it is thought that prolonged dry conditions led to mortality of juveniles and recruitment failure, ultimately causing population senescence and extinction.

Conservation Actions [top]

Conservation Actions: This snail was present in the Aldabra Special Reserve.

Citation: Gerlach, J. 2009. Rhachistia aldabrae. The IUCN Red List of Threatened Species 2009: e.T168122A6454921. . Downloaded on 21 May 2018.
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