in Sri Lanka - Ministry of Environment

Taxonomy and Conservation Status of the Freshwater Crabs(Crustacea: Decapoda) in Sri LankaM. M. Bahir and D. E. GabadageTaprobanica Nature Conservation Society, 150/6 Stanley Thilakaratne Mawatha, NugegodaIntroductionThe exploration of Sri Lanka’s freshwater crabs began 132 years ago with the descriptionin 1880 of Thelphusa [Perbrinckia] enodis and Thelphusa [Ceylonthelphusa] rugosa by theAmerican zoologist, J. S. Kingsley. This was followed by several studies by Rathbun, (1904)Roux (1915) and Fernando (1960). The first revision of the freshwater crab fauna of Sri Lankawas carried out by Bott in 1970. A resurgence in the research interest on Sri Lanka’s freshwatercrabs was observed in 1990’s following a joint exploration carried out by the National Universityof Singapore and the Wildlife Heritage Trust of Sri Lanka (Ng, 1994, 1995a, 1995b; Bahir,1998, 1999; Ng & Tay, 2001; Bahir & Ng, 2005; Bahir & Yeo, 2005).Up to 1994, only eight valid species of freshwater crabs belonging to four genera were recognizedfrom Sri Lanka. The extensive exploration work carried out by the National University of Singaporeand the Wildlife Heritage Trust of Sri Lanka resulted in the discovery of many new species andgenera of freshwater crabs taking the total number of species to 51 and genera to 7. Based onthe present state of knowledge of the peninsular Indian carcinofauna (Bossuyt et al., 2004; Bahir& Yeo, 2005), 50 Sri Lankan freshwater-crab species and five of the genera (Ceylonthelphusa,Perbrinckia, Mahatha, Clinothelphusa and Pastilla) are endemic to Sri Lanka while the twolowland genera, Oziothelphusa and Spiralothelphusa, are shared with southern India. All the SriLankan freshwater crabs belong to a single family, Gecarcinucidae.DistributionSri Lanka supports a rich freshwater crab assemblage in comparison with other similar, wellstudiedtropical Asian countries such as Peninsular Malaysia and Singapore, which togetherhave a territory about twice the extent of Sri Lanka, and yet about the same number offreshwater crab species (Ng, 1988), while Taiwan which is about little over half the size of SriLanka (36,000 km 2 ) has 34 species (Ng et al., 2001). Another unique feature of Sri Lankanfreshwater crabs is that they show 98.04% endemicity which has not been observed in anyother faunal group in Sri Lanka.Nearly half the freshwater crabs known to date (23 species) are point endemics, renderingthem extremely vulnerable to habitat loss, degradation and stochastic events. The reason asto why freshwater crabs show such a highly restricted distribution is unclear. However, thisphenomenon has been observed to a lesser extent in other taxa with low mobility such asamphibians and reptiles as well. Out of the 51 known species of freshwater crabs 41 (80%) arerestricted to the wet zone. Only 4.6% of the wet zone (800 km 2 ) now contains natural forest.The wet zone of Sri Lanka also has a very high population density (700 per km 2 ) one of thehighest population densities observed in all of the global biodiversity hotspots of the world(Cincotta et al., 2000). Therefore, conserving freshwater crabs in such a human-dominatedlandscape is going to be a challenging task.58