Rhachistia aldabrae

Taxonomy

Assessment Information

Geographic Range

Population

Habitat and Ecology

Threats

Conservation Actions

Bibliography

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Taxonomy [top]

Kingdom	Phylum	Class	Order	Family
ANIMALIA	MOLLUSCA	GASTROPODA	STYLOMMATOPHORA	CERASTIDAE

Scientific Name:

Rhachistia aldabrae

Species Authority:

(Martens, 1898)

Common Name/s:

English

–

Aldabra Banded Snail

Assessment Information [top]

Red List Category & Criteria:	Extinct ver 3.1
Year Assessed:	2009
Assessor/s:	Gerlach, J.
Reviewer/s:	Pollock, C.M., Miller, R.M. & Seddon, M.
Justification: 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:	Regionally extinct: Seychelles (Aldabra)
Range Map:	(click map to view full version)

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.

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.

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.
Systems:	Terrestrial

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.

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.

Conservation Actions:

This snail was present in the Aldabra Special Reserve.

Bibliography [top]

	Gerlach, J. 2006. Terrestrial and Freshwater Mollusca of the Seychelles Islands. Backhuys, Leiden. Gerlach, J. 2007. Short-term climate change and the extinction of the snail Rhachistia aldabrae (Gastropoda: Pulmonata). Biology Letters 3: 581-585. Gerlach, J. In prep. Declines in terrestrial Molusca on Aldabra atoll. Gerlach, J., Matyot, P. and Samways, M.J. 2005. Developing strategies for invertebrate conservation, the case of the Seychelles islands. Phelsuma: 9-12. IUCN. 2009. IUCN Red List of Threatened Species (ver. 2009.2). Available at: www.iucnredlist.org. (Accessed: 3 November 2009).

Gerlach, J. 2006. Terrestrial and Freshwater Mollusca of the Seychelles Islands. Backhuys, Leiden.

Gerlach, J. 2007. Short-term climate change and the extinction of the snail Rhachistia aldabrae (Gastropoda: Pulmonata). Biology Letters 3: 581-585.

Gerlach, J. In prep. Declines in terrestrial Molusca on Aldabra atoll.

Gerlach, J., Matyot, P. and Samways, M.J. 2005. Developing strategies for invertebrate conservation, the case of the Seychelles islands. Phelsuma: 9-12.

IUCN. 2009. IUCN Red List of Threatened Species (ver. 2009.2). Available at: www.iucnredlist.org. (Accessed: 3 November 2009).

Citation:	Gerlach, J. 2009. Rhachistia aldabrae. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. <www.iucnredlist.org>. Downloaded on 10 February 2012.
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