|Scientific Name:||Ceylonthelphusa nana|
|Species Authority:||Bahir, 1999|
|Taxonomic Notes:||This species was formerly included in the Parathelphusidae but has recently been reassigned to the Gecarcinucidae; Parathelphusidae is now regarded as a junior synonym of Gecarcinucidae (Klause et al. in press).
|Red List Category & Criteria:||Critically Endangered B1ab(iii)+2ab(iii) ver 3.1|
|Assessor(s):||Bahir, M.M., Ng, P.K.L., Crandall, K. & Pethiyagoda, R. and Cumberlidge, N.|
|Reviewer(s):||Darwall, W. (IUCN Freshwater Biodiversity Assessment Unit), Pollock, C.M. (IUCN Red List Unit) and McIvor, A.|
Listed as Critically Endangered because this is a very rare species, with extent of occurrence (EOO) and area of occupancy (AOO) both <10 km², and it is known from only three locations. Currently the range area for this species is not protected and habitat is subject to degradation because of direct human impacts.
|Range Description:||Endemic to Sri Lanka. Extent of occurrence 5 km². Known from three localities in southwestern Sri Lanka in the Bentota and Gin River basins (Bahir, 1999, original description). Found at Pituwala (06°15'N 80°12'E) near Elpitiya and Amugoda near Elpitiya (06°19'N 80°13'30'E); at a streamlet in Kottawa Proposed Forest Reserve, Galle District, southwestern Sri Lanka, in the Bentota and Gin River basins.|
|Range Map:||Click here to open the map viewer and explore range.|
|Habitat and Ecology:||Occurs in freshwater aquatic habitats in the wet zone area of Sri Lanka. Under moist stones and leaf litter in a small stream. Occurs in very shallow (<5 cm deep) water in small, rainforest streams, under rocks on stream margins, and among wet, fallen leaves among boulders in the stream.|
Sri Lanka’s aquatic habitats are threatened by invasive alien species (>90 percent of the freshwater-fish biomass comprises exotics: Pethiyagoda 1994) and pollution, while its forests are threatened by encroachment and illegal produce extraction. The greater threats to the island’s remaining wet zone habitats are perceived to be from indirect sources exacerbated by ‘island effects’ resulting from fragmentation— invasive species, pesticide influx, edge effects, local climate change and rainwater acidification.
Pesticides are a serious concern given that these substances are freely and widely used in Sri Lanka. Regulation presently addresses only human safety issues, and not impacts on other non-target organisms or the environment in general (Anon. 1980). Given that 24 of Sri Lanka’s 49 freshwater crab species are restricted to montane and sub-montane habitats, poor sloping-land management and unwise land-use change in the highlands continues to be a serious problem (Hewawasam et al. 2003). An estimated 292 MT ha-1 yr-1 of topsoil is lost to erosion from these lands, degrading habitats and increasing silt loads in streams and rivers (ADB 2003).
Even species with wide ranges and apparent tolerance of land-use changes could suffer catastrophic declines as a result of changes, for example, in land developments, hydrology or pesticide-use regimes. For example, the populations of two species of widely-distributed freshwater fishes (Labeo lankae and Macrognathus aral) assessed in 1980 as "common" (Senanayake 1980) crashed within a decade, without warning, for reasons still unknown— they are now presumed extinct (Pethiyagoda 1994).
The long-term security of Sri Lanka’s biodiversity will depend on minimizing fragmentation impacts through effective land-use planning and restoration initiatives while maximizing habitat connectivity between forest sites. Such goals can be met only through a policy framework built on sound scientific data, implemented through sustained, long-term financing mechanisms. Planning on such a scale is not imminent in Sri Lanka, and in the mean time, it is best that conservation activities be aimed primarily at preserving the integrity of sites and habitats while at the same time closely monitoring key populations.
The conservation of freshwater crabs hinges almost entirely on preserving patches of natural forest large enough to maintain the good water quality of the original streams. Many parathelphusids are extremely sensitive to polluted or silted waters, and will not survive when exposed to these factors.
|Citation:||Bahir, M.M., Ng, P.K.L., Crandall, K. & Pethiyagoda, R. and Cumberlidge, N. 2008. Ceylonthelphusa nana. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 04 July 2015.|
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