Distribution notes on the Endangered freshwater crab Ceylonthelphusa armata Ng (1995) (Crustacea: Brachyura: Gecarcinucidae) in Sri Lanka

U.S.C. Udagedera 1, Dinesh E. Gabadage 2 & M.M.M. Najim 3

 

1­ Graduate Student, Faculty of Graduate Studies (FGS), University of Colombo, Sri Lanka

2 Biodiversity Conservation Society, Number 150/6, Stanly Thilakaratne Mawatha, Nugegoda, Sri Lanka

3 Department of Zoology and Environmental Management, Faculty of . Science, University of Kelaniya, Kelaniya, Sri Lanka

1 uscudagedara@gmail.com (corresponding author), 2 degabadage@gmail.com, 3 mnajim@kln.ac.lk

 

 

 

doi: http://dx.doi.org/10.11609/JoTT.o3949.7791-4 | ZooBank: urn:lsid:zoobank.org:pub:14667660-C269-4428-8619-EB5A04F1524B

 

Editor: Raymond Henry, Auburn University, Auburn, USA. Date of publication: 26 September 2015 (online & print)

 

Manuscript details: Ms # o3949 | Received 24 February 2014 | Final received 21 August 2015 | Finally accepted 30 August 2015

 

Citation: Udagedera, U.S.C., D.E. Gabadage & M.M.M. Najim (2015). Distribution notes on the Endangered freshwater crab Ceylonthelphusa armata Ng (1995) (Crustacea: Brachyura: Gecarcinucidae) in Sri Lanka. Journal of Threatened Taxa 7(11): 7791–7794; http://dx.doi.org/10.11609/JoTT.o3949.7791-4

 

Copyright: © Udagedera et al. 2015. Creative Commons Attribution 4.0 International License. JoTT allows unrestricted use of this article in any medium, reproduction and distribution by providing adequate credit to the authors and the source of publication.

 

Funding: None.

 

Conflict of Interest: The authors declare no competing interests.

 

Acknowledgements The authors thank M.M. Bahir (Researcher at Biodiversity Conservation Society & Biodiversity Education and Exploration Society) for confirming the identity of the crabs in the field, providing literature, reviewing this note and encouraging this study. The authors also thank Prof. U. S Amarasinghe and Thasun Amarasinghe for reviewing this article. We thank Madhava Bothejue for the photographs.

 

 

 

Abstract: There are 52 species of freshwater crabs in Sri Lanka and 51 of them are endemic. There are several species that are known only from a single locality. Ceylonthelphusa armata is such a species, and we have initiated a study to record the distribution of this species as its typical locality is heavily polluted at Kadugannawa. At present C. armata is known from six localities, and this information will be useful to facilitate the conservation of the species by assessing the Red List.

 

Keywords: Conservation, endemic, invertebrates, pollution, threatened taxa.

 

 

There are 52 species of freshwater crabs known from the island of Sri Lanka with 51 endemics, many of which are threatened taxa (Bahir et al. 2005; Ng et al. 2008; Beenaerts et al. 2010). As restricted endemism has been the main criterion for categorizing them as threatened (Bahir et al. 2005), it is important to have accurate records of the distribution of the species. The endemic freshwater crab genus Ceylonthelphusa is represented by 17 species with 12 categorized as Critically Endangered, three as Endangered and one Near Threatened (MOE 2012). More than 50% of freshwater crabs of the island are known from very restricted localities. More than half of the Ceylonthelphusa species is also known from a single locality each and these are categorized as Critically Endangered. The habitat of Ceylonthelphusa armata (Ng 1995) is being exploited by human activities (Images 1a–c) such as washing vehicles, garbage dumping and burning, and commercial activities such as installation of fruit stalls. Therefore, a study was initiated to document the distribution of Ceylonthelphusa armata (Ng, 1995), which was common two decades ago at its type locality, Galavidaputhena, Kadugannawa (07015’N & 80028’E altitude 300m), beside the Kandy-Colombo main road.

Ceylonthelphusa armata (Image 2a–c) was described in a revision (Ng 1995) of the genus Perbrinckia (Bott 1969). Initially there was a single species in that genus, and in the revision (Ng 1995) added nine more new species to the genus, bringing the total number of species within the genus up to 10. Subsequently, (Ng & Tay 2001) studied the Sri Lankan freshwater crabs and redefined the genera Ceylonthelphusa (Bott 1970) and Perbrinckia based on the characteristics of the second male pleopod. The key character separating these two genera is the length of the distal segment of the second pleopod of the male; in Perbrinckia the distal segment is about 0.2–0.3 times the length of the basal segment while in Ceylonthelphusa it is relatively longer (Ng & Tay 2001; Bahir & Ng 2005).

 

 

Material and Methods

The type locality of Ceylonthelphusa armata is Kadugannawa located within Maha Oya catchment (Ng 1995). In this study C. armata’s distribution was examined at several locations upstream and downstream to the type locality. These sites were selected within the Maha Oya catchment. Twelve locations at which streamlets of Maha Oya originate were selected as the sampling sites, which were: Miyanagolla (07006’N & 80029’E; 1000m); Udahenthenna (07006’N & 80032’E; 850m); Selawa (07009’N & 80031’E; 300m); Deiyanwala (07008’N & 80028’E; 400m); Kehelpannala (07010’N & 80032’E; 400m); Duldeniya (07010’N & 80028’E; 350m); Ambadeniya (07012’N & 80029’E; 300m); Mahanthegama (07013’N & 80031’E; 400m); Urakanda (07012’N & 80025’E; 500m); Bathalegala (07011’N & 80026’E; 798m); Welimanna Village (07009’N & 80027’E; 400m); Hulankaduwa (07005’N & 80026’E; 500m).

The crabs were hand collected with minimum disturbance to their microhabitats by slowly removing rocks, pebbles and root outcrops on wet rocks, and the external characters of the animals were observed by using hand lenses. Live photographs were taken to study the dorsal, frontal and ventral views, and the crabs were then released back into their habitats (Image 2a–c). Species identifications and nomenclature were followed based on Ng (1995), Ng & Tay (2001), Bahir & Ng (2005), Klaus et al. (2009) and Beenaerts et al. (2010).

 

 

 

 

Observations

In this study C. armata from five more localities (Table 1) were recorded within Kegalle District (Fig. 1) assuming that the present distribution of the species will be useful to facilitate its conservation towards assisting the Sri Lankan Red Listing of carcinofauna according to IUCN criteria (IUCN 2001).

1. We found that C. armata was common (authors termed it common when an individual spotted five or more adult crabs within 30 minutes of search from a particular location) in Urakanda (07012’N & 80025’E; 500m) near Asmadala. The crabs were found under stones and under root outcrops on wet rocks adjacent to a small stream in a shady area.

2. We found that C. armata was uncommon (authors termed it uncommon when an individual spotted three or four adult crabs within 30 minutes) in Bathalegala (07011’N & 80026’E; 798m). The crabs were observed from a small cave, under stones in wet soil.

3. We also found C. armata which was uncommon from Welimanna Village (07009’N & 80027’E; 400m) near Aranayake. The crabs were observed from a wet rock, and in crevices with root outcrop and leaf litter.

4. We found C. armata which was common from Hulankaduwa (07005’N & 80026’E; 500m) near Ambalakanda. The crabs were observed under stones and rocks in a moist, shady area.

5. We found that C. armata was common in Deiyanwala near Aranayake (07008’N & 80028’E; 400m). The crabs were found under stones and under root outcrops on wet rocks adjacent to a small stream in a shady area.

It is interesting to note that this species was observed from Welimanna and Bathalegala only in the wet months, and our attempts to record the species in the dry months of January and February were unsuccessful. We hypothesize that this crab moves downstream to reach wet areas or goes underground until the rainy season, which is worth further investigation.

The type locality of C. armata is heavily polluted due to dumping of trash by local traders and local tourists. We found that many microhabitats of C. armata were heavily polluted and as a result we failed to observe crabs (Image 1c) from some of the microhabitats where they were recorded two decades ago. One of us (DG) recorded this species as common from six moist areas/small stream banks at the type locality in 1994, but unfortunately now it is restricted to only a few sites and the species has become rare in its type locality. We assumed that C. armata cannot live in polluted water. We believe that conservation managers should take immediate action (e.g., control pollution and burning) to conserve the type locality and microhabitats of C. armata at Kadugannawa. In addition, we observed Ceylonthelphusa rugosa Kingsley (1880) to be sympatric with C. armata in all the six sampling localities that were observed. It is essential to record the known habitats of freshwater crabs like C. armata to assess their conservation status in the long run, because one of us (DG) is in the process of observing the freshwater crab populations in their type localities.

 

 

Conclusion

At present, the distributions of C. armata include six localities with existing information and we believe it is important to record the extent of occurrence of the threatened species of freshwater crabs to evaluate during the Red Listing process. We found that the type locality of C. armata is threatened by pollution and economic activities. Immediate measures should be taken against pollution and fire. In the future, this information may facilitate conservation assessment of C. armata because at present the Red List is recognized as a conservation tool (Vié et al. 2008). Not many invertebrate groups of Sri Lankan taxa are assessed to produce the Red List, but it is important that the freshwater crabs of Sri Lanka are already assessed according to the IUCN criteria to prioritize freshwater crab conservation (Bahir et al. 2005; IUCN 2007; MOE 2012).

 

 

References

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