in Sri Lanka - Ministry of Environment

ThreatsSri Lanka’s aquatic habitats are threatened by invasive alien species. Further, influx of fertilizerand pesticides, local climate change (Schaefer, 1998), rainwater acidification and increasederosion leading to sedimentation of water bodies can be sited as other major threats on thehabitats of the freshwater crabs. The water yield in the freshwater systems is also influencedto a great extent by the loss of forest cover due to encroachment and illegal timber extraction.Pesticides are key pollutants of many aquatic systems as these substances are freely andwidely used in Sri Lanka. Regulation presently addresses only human safety issues, and notimpacts on other non-target organisms or the environment in general (Anon., 1980). Sincenearly half the freshwater crab species (24) of Sri Lanka are restricted to montane andsub-montane habitats, poor sloping-land management and unwise land-use change in thehighlands continues to be a serious problem (Hewawasam et al., 2003). An estimated 292MT ha -1 yr -1 of topsoil is lost to erosion from these lands, degrading habitats and increasingsilt loads in streams and rivers (ADB, 2003). A handful of freshwater-crab species have widedistributions and are clearly tolerant of land-use change, given that they persist in rice fields (e.g.Oziothelphusa spp.) and tea plantations (e.g. Ceylonthelphusa rugosa and Ceylonthelphusasoror). Even such species, however, could suffer catastrophic declines as a result of changesin the hydrology or pesticide-use regimes.ConservationGiven the fact that most of the freshwater crabs have been discovered over the last twodecades and they are poorly represented in museum collections, there is no reliable historicalbaseline against which to judge trends in distributions or population changes. Therefore it isnot possible to ascertain whether there have been any recent extinctions in the freshwatercrab fauna as has been recorded for flowering plants (~ 130 species: Dassanayake et al.,1980–2004); amphibians (19 species: Manamendra-Arachchi & Pethiyagoda, 2005; Stuartet al., 2004; Meegaskumbura et al., 2012; Wickramasinghe et al., 2012); and freshwater fish (2species: Pethiyagoda, 1994). However, according to the outcome of the current conservationstatus review of the freshwater crabs of Sri Lanka, nearly 90% of the freshwater crabs in SriLanka are globally threatened with 66% being listed under the critically endangered category.Thus, conservation of the entire freshwater crab fauna of Sri Lanka, given its remarkablediversity, richness and endemism, is a matter of the highest priority. The urgency to takeappropriate conservation action is more so given the fact that freshwater crabs are not targetedfor exploitation in Sri Lanka and yet a high proportion of them are globally threatened. It is notclear whether the exceedingly small populations seen in many species of crabs are a naturalphenomenon or have resulted due to a sudden decline. Further, it is not known whether thefreshwater crabs naturally have a severely restricted distribution, resulting in the extremelysmall extents of occurrence that is observed for nearly 90% of the crabs in Sri Lanka or thissituation has resulted due to habitat loss or some other driver operating on this taxa.As very little is known about the ecology of the freshwater crabs of Sri Lanka, it is prudentto take the precautionary approach when determining strategies for conserving this fauna.Therefore, the conservation assessment made here should be accepted at face value, andrecovery strategies devised accordingly, until more data become available to support theconclusion that each threatened species is in fact secure.59