Chapter 6. Freshwater crabs of the Indo-Burma hotspot: diversity, distribution, and conservation Neil Cumberlidge1, Peter K.L. Ng2 and Darren C.J. Yeo2 6.1 Overview of the freshwater crab fauna of the Indo-Burma hotspot ..............................................................................................................102 6.1.1 Biogeographic patterns ....................................................................................................................................................................................103 6.2 Conservation status ....................................................................................................................................................................................................103 6.3 Patterns of species richness .......................................................................................................................................................................................104 6.3.1 All freshwater crab species: interpretation of distribution patterns.....................................................................................................105 6.3.2 Threatened species distribution patterns ....................................................................................................................................................106 6.3.3 Restricted range species ...................................................................................................................................................................................107 6.3.4 Data Deficient species......................................................................................................................................................................................108 6.4 Major threats ................................................................................................................................................................................................................109 6.4.1 Habitat destruction ..........................................................................................................................................................................................109 6.4.2 Pollution .............................................................................................................................................................................................................110 6.4.3 Natural predators and competition with introduced species ................................................................................................................110 6.4.4 Taxonomic issues ..............................................................................................................................................................................................110 6.5 Research actions required .........................................................................................................................................................................................110 6.6 Conservation recommendations ............................................................................................................................................................................. 111 6.7 References ..................................................................................................................................................................................................................... 111 6.1 Overview of the freshwater crab fauna The number of species of freshwater crabs found in the Indo- of the Indo-Burma hotspot Burma hotspot has grown steadily as the number of revisionary taxonomic studies in this part of Asia has increased (Rathbun Freshwater crabs are among the most important invertebrates 1902, 1904, 1905; Alcock 1909, 1910; Balss 1914, 1918, 1923; inhabiting Asian inland waters and these large and conspicuous Bott 1966, 1968, 1970; Ng 1988, Ng and Naiyanetr 1993, 1995; crustaceans are present in almost all freshwater habitats from Yeo and Ng 1997, 1998, 1999, 2003, 2004, 2005, 2007, 2010; mountain streams to large lowland rivers and smaller water Yeo et al. 1999, Yeo and Naiyanetr 1999, 2000, 2010; Ng and Yeo bodies (Yeo et al. 2008). The present work focuses on the 2001, Yeo 2004, 2010; Yeo and Naruse 2007, Yeo et al. 2008, Ng freshwater crabs of the biodiversity hotspot that is centred in et al. 2008, Naiyanetr and Yeo 2010, Naruse et al. 2011). These the Indo-Burma region that lies in five countries: Thailand, works have resulted in the description of large numbers of new Cambodia, Viet Nam, Lao Peoples Democratic Republic (Lao species and new genera. The revisions at the family-level have PDR), and the eastern part of Myanmar. A small portion of included the revalidation of the subfamily Potamiscinae of the Malaysia (the northwestern states of Perlis and Kedah) falls Potamidae Ortmann, 1896, to include all east Asian potamids, within the southern tip of the Indo-Burma region (Figure 1.1); including those in the Indo-Burma hotspot (Yeo and Ng 2003), however, this contributes only four species (one endemic) to and the reassignment to the Gecarcinucidae Rathbun, 1904 of the region’s richness, representing less than 5% of the country’s all species formerly assigned to the Parathelphusidae following freshwater crab fauna, as such Malaysia will be excluded from our the synonymy of these two families, with priority going to the discussions of country level patterns in this paper. Specifically, the Gecarcinucidae (Klaus et al. 2009). Indo-Burma region as considered here extends from the Salween eastwards, and includes the Thai peninsula, coastal basins in In biogeographical terms the Indo-Burma hotspot lies in the Myanmar, Thailand, and Indochina, and the major river basins Oriental zoogeographical region, an area that includes India, (Mekong, Chao Praya, Hong and Da, Mae Klong), excluding the southern China, and Southeast Asia as far east as Wallace’s line Chinese parts of these river basins. (Yeo et al. 2008). The Oriental region is the most taxonomically 1 Department of Biology, Northern Michigan University, Marquette, Michigan 49855, USA. [email protected]. 2 Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Republic of Singapore 117543. [email protected], [email protected]. 102 diverse part of the world with over 900 species of freshwater crabs et al. 2008). However, with only a few exceptions, there is no in 154 genera and two families, totals that are markedly higher close correlation between freshwater crab distribution patterns than those of the faunas of the Neotropical region (50 genera, and freshwater ecoregion boundaries found in the Indo-Burma 298 species, two families) and the Afrotropical region (18 genera, hotspot. The only instances where freshwater crab distribution 133 species, two families) (Yeo et al. 2008, Cumberlidge et al. coincides with ecoregion boundaries are those species that have a 2009). restricted distribution. The Indo-Burma hotspot hosts 182 known species of freshwater Most freshwater crabs are nocturnal scavengers or opportunistic crabs in 55 genera and two families, the Gecarcinucidae (45 predators, and some species have economic and ecological species, ten genera) and the Potamidae (136 species, 45 genera) importance (Yeo et al. 2008). For example, some species are rice (Ng et al. 2008, Yeo et al. 2008, Cumberlidge et al. 2009). This field pests, some are a source of protein for people, and other species fauna is more diverse than previously assumed, and there are many have medical importance serving as the second intermediate host more species still to be discovered. The freshwater crab genera of of the parasitic human lung fluke, Paragonimus. Some species the Indo-Burma hotspot is highly endemic at the country level – of freshwater crabs also serve as bio-indicators of ecosystem 92% of the potamid species, and 76% of the gecarcinucid species disruption, some are threatened by collection for the aquarium endemic (Yeo et al. 2008, Cumberlidge et al. 2009). trade, and some are even conservation icons, such as the Thai Royal crabs: Phricotelphusa sirindhorn (LC), Indochinamon 6.1.1 Biogeographic patterns bhumipol (EN), and Thaiphusa sirikit(LC). The Indo-Burma hotspot shows a distinct north-south latitudinal trend that corresponds to the broader regional trend 6.2. Conservation status reported by Yeo and Ng (2003), whereby potamids dominate over gecarcinucids in the north, but gecarcinucids dominate The conservation status of 173 Indo-Burma’s known freshwater over potamids in the south. For example, in China the ratio of crab fauna was assessed as part of the global study by Cumberlidge potamids:gecarcinucids is 91:9, but this ratio changes further et al. (2009) using the IUCN Red List Categories and Criteria at south, and is 73:27 in Indochina, and 51:49 in Peninsular the global scale (IUCN 2003) and individual species assessments Malaysia (Yeo and Ng 1998). In the Indo-Burma hotspot dealt are available through the IUCN Red List website (www. with here, the Potamidae constitute approximately 75% of the iucnredlist.org). The conservation assessments of nine species, known fauna, with the Gecarcinucidae making up the remaining mainly recently described taxa, are in progress and are considered 25%. In the northern part of this region gecarcinucids are poorly provisional. The Cumberlidge et al. (2009) study included represented in Myanmar and Lao PDR (only 9% and 12%,