Samoana diaphana 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Mollusca Gastropoda Stylommatophora Partulidae

Scientific Name: Samoana diaphana (Crampton & Cooke, 1953)
Common Name(s):
English Polynesian Tree Snail, Delicate Samoana tree snail, Moorean Viviparous Tree Snail
Taxonomic Notes: Molecular analysis has revealed the possible existence of S. diaphana, previously believed endemic to Moorea, on Tahiti (O'Foighil, pers. comm.).

Assessment Information [top]

Red List Category & Criteria: Endangered B2ab(i,ii,iii) ver 3.1
Year Published: 2012
Date Assessed: 2010-10-21
Assessor(s): O'Foighil, D.
Reviewer(s): Cowie, R., Barker, G., Triantis, K., García, N. & Pippard, H.
Contributor(s): Coote, T.
This species has an inferred area of occupancy of 20 km2, it has been reported from three locations (5 known sites; one on Moorea, four on Tahiti) and the extent and quality of its habitat is known to be declining. Thus, this species is listed as Endangered. Continued biosecurity vigilance is critical to prevent further invasive species establishments in this species' habitat. Surveys to determine the current distribution of this species and population size, status and trends are also recommended, as is site protection and habitat monitoring.
Previously published Red List assessments:

Geographic Range [top]

Range Description:

This species is endemic to French Polynesia and is found on Moorea (type locality) and also the neighboring island of Tahiti. It was thought to be extinct (Coote and Loève 2003), but it is now known to survive in four Tahitian and one Moorean localities (two and one locations, respectively).

This species was described by Cooke and Crampton (1953) using Moorean specimens collected in 1934 from montane forest habitat (~660 m altitude). Kondo (1973) also listed it as a Moorean endemic; J.B. Burch having collected it on a montane ridge in 1970.  However, Johnson et al. (1986) recorded it from a montane site on Tahiti (co-occurring with Samoana burchi) as well as from 4 Moorean sites: two lower elevation valleys in the northwest of the island where it co-occurred with S. attenuata; and two higher elevation localities in the southeast of the island.

Surviving populations were confirmed using morphological and molecular diagnoses to occur on two montane sites on Tahiti: Mts. Aorai and Pihaaiateta (Lee et al. 2009). In addition, a photographed montane Moorean individual (380 m elevation on a ridge above Col des 3 Cocotiers) was identified as a surviving S. diaphana (Lee et al. 2009). Additional Tahitian survivors were recorded by Trevor Coote in 2010 in two other sites: Mt. Mahutaa (high altitude) and Fautaua Valley (lower altitude, co-occurring with Partula clara).

Considering that the species is known from five sites, the inferred area of occupancy is 20 km2.

Additional data:
Estimated area of occupancy (AOO) - km2:20Continuing decline in area of occupancy (AOO):Yes
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:
Continuing decline in extent of occurrence (EOO):YesExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:3Continuing decline in number of locations:Unknown
Extreme fluctuations in the number of locations:NoLower elevation limit (metres):300
Upper elevation limit (metres):1300
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The five known site records consist of either a single observed snail or else a small cluster.
Current Population Trend:Unknown
Additional data:
Continuing decline of mature individuals:Unknown
Extreme fluctuations:NoPopulation severely fragmented:Yes
Continuing decline in subpopulations:Unknown
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:This is an arboreal species found in rain forest, in both valleys and montane habitats.
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):0-3
Congregatory:Congregatory (and dispersive)

Use and Trade [top]

Use and Trade: There is no known use or trade.

Threats [top]

Major Threat(s):

The primary threat is posed by the introduced predatory land snail Euglandina rosea. The predator has extirpated most valley partulid populations since its introduction in 1975 (Tahiti) and 1977 (Moorea) (Coote and Loève 2003, Coote 2007) and extends at least to an altitude of 1,400 m into the montane forests of Tahiti (Lee et al. 2008, 2009; Gargominy 2008).  Lower elevation  populations are therefore directly exposed to the predator and lower elevation populations on Moorea appear to have been extirpated, with only one record of a surviving montane Moorean population. On Tahiti, there is one known surviving valley population and three known montane populations. It is not clear how serious the threat is for surviving montane Tahitian populations because the predator may be relatively ineffective at these altitudes (Gerlach 1994, Gargominy 2008, Lee et al. 2009). Montane Tahitian habitats are relatively inaccessible and undisturbed; but there is some loss of habitat due to anthropogenic action, especially fire (Gargominy 2008).

Conservation Actions [top]

Conservation Actions: No directed conservation efforts are known to be in place for this species. Field work to define the current distribution of this species, as well as research on its population status and trends, is required. Identification of priority sites for species conservation (e.g. key biodiversity areas that include threatened land snails) and reducing the impacts of human activities, and invasive species, are also urgently needed.

Citation: O'Foighil, D. 2012. Samoana diaphana. The IUCN Red List of Threatened Species 2012: e.T19880A2537615. . Downloaded on 20 September 2018.
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