Distribution of Cryptopotamon anacoluthon (Kemp, 1918) (Crustacea: Brachyura: Potamidae), a freshwater crab endemic to Hong Kong

Cryptopotamon anacoluthon (Kemp, 1918) is a tropical freshwater crab currently considered endemic to Hong Kong. The species is more widely distributed than previously known and potentially occurs outside Hong Kong; however, the habitat of the species is under threat due to developmental activities and channelisation of watercourses. It is hoped that understanding of the distribution of this species will aid in its conservation.

D a v fi d J o h n S t a n t o n , M fi c h a e l R o b e r t s o n L e v e n & T omm y C h u n g H o n g H u fi 2 6 F e b r u a r y 2 0 1 7 | V o l . 9 | N o . 2 | P p . 9 7 8 6 -9 7 9 4 1 0 . 1 1 6 0 9 / j o t t . 3 0 0 7 . 9 . 2 . 9 7 8 6 -9 7 9 4 T h r e a t e n e d T a x a

INTRODUCTION
First described from Hong Kong, Cryptopotamon anacoluthon (Kemp, 1918) is a tropical freshwater crab (Image 1). This species appears to be relatively stenotopic and is found in shaded shallow streams with clear or unpolluted, fast-flowing waters, rocky substratum, and leaf-litters, which serve as shelter and food (Ng & Dudgeon 1992;Esser & Cumberlidge 2008). The species is listed under the 'Vulnerable' (VU) category of the IUCN Red List of Threatened Species because it might be under long-term threat from rapid anthropogenic changes and also due to its limited distribution (Esser & Cumberlidge 2008 IUCN stated that this species may be threatened by future degradation of clean streams, a result of human population increases and industrial and agrarian development and, incorrectly, that it is not found in a protected area (Esser & Cumberlidge 2008). According to a local conservation assessment, the species is listed as being of Potential Global Concern (Fellowes et al. 2002).
While some Chinese freshwater crabs have been quite well studied, most species are either known only from the type locality or from just a few localities. In these situations, further collections are necessary to ascertain their actual distributions (Cumberlidge et al. 2010). Therefore, we have reviewed literature and made field observations in Hong Kong in order to provide additional information on the distribution of C. anacoluthon.

Study Area
The present study area, Hong Kong Special Administration Region (SAR), People's Republic of China (PRC) (22 0 09'-22 0 37'N & 113 0 50'-114 0 30'E) is situated on the south China coast to the east of the Pearl River (Zhujiang) estuary (Fig. 1). Hong Kong occupies an area of 1,100km 2 and is made up of a section of the Chinese Mainland (Kowloon and the New Territories, 793km 2 ) and islands, of which Hong Kong and Lantau are the largest (78km 2 and 147km 2 , respectively). The topography of Hong Kong is generally rugged with little flat land; much of the flatter areas (c. 60km 2 ) are a result of land reclamation (Dudgeon & Corlett 2004). The Shenzhen River to the north largely separates Hong Kong from the Shenzhen Special Economic Zone of the PRC.
The climate of Hong Kong is distinctly monsoonal and despite its subtropical nature has well-defined seasons associated with the east Asian monsoons (Carey et al. 2001). During winter, the continental high-pressure region over Siberia and Mongolia results in north or northeasterly winds that bring cool, dry air to Hong Kong (Dudgeon & Corlett 2004).

Literature review
A review of literature was undertaken to examine the known distribution of C. anacoluthon. Full details of Image 1. Cryptopotamon anacoluthon (Kemp, 1918) in its natural habitat this review and sources can be seen in Appendices 1 and 2. Hong Kong SAR has a robust environmental impact assessment (EIA) process and numerous developments requiring EIA studies have taken place in Hong Kong; potentially affecting streams where this crab occurs. Such EIA studies invariably require surveys of the streams that may be affected. Accordingly, desktop studies of EIA reports were made from the documents available at the Environmental Protection Departments website (http://www.epd.gov.hk/eia/) in order to comprehensively review the available ecological findings from these studies. Additional data was obtained from unpublished studies and the authors' own unpublished results of previous survey findings.

Observations
A review of 110 EIA reports, published between 2002 and 2016, was undertaken and these are listed in Appendix 1. The findings of the present review, combined with additional data obtained from unpublished studies have revealed that C. anacoluthon is known from at least 25 locations at 22 sites in Hong Kong (Appendix 1, C. anacoluthon have been found mostly in fast flowing watercourses, which pass through semi-mature secondary woodland with limited anthropogenic influences, and with altitudinal range from 8m to 827m. Examples of typical watercourses where the crab has been observed are shown in Image 2. Field observations by the authors are that numbers recorded are generally low, i.e., only several individuals.

Distribution and habitat requirements of C. anacoluthon
Esser & Cumberlidge (2008) stated that C. anacoluthon occurred in four locations in Hong Kong and the probable range may extend into coastal Guangdong. From the present review, however, it is clear that the species is more widespread than previously thought, i.e., with 25 identified locations and approximately 200km 2 area of occupancy. Esser & Cumberlidge (2008)

Distribution of Cryptopotamon anacoluthon in Hong Kong
Stanton et al.
suggested that the population of C. anacoluthon is not severely fragmented, though the watercourses within Hong Kong are often fragmented (Stanton & Leven 2016) and do not share downstream confluences, a result of urbanisation. Many watercourses have been piped or channelised in their lower sections, and these modifications are likely to inhibit the movement of crabs between catchments. Hence, it is likely that within this area of occupancy there are now a number of more or less isolated sub-populations.

Mitigation and Conservation
According to IUCN, no conservation measures are known to be in place for C. anacoluthon, and the species is not found in a protected area (Esser & Cumberlidge 2008); however, one of the sites listed by Esser & Cumberlidge (2008) was in fact protected at that time, as it is today. They also mentioned that habitat loss and pollution are the major threats to C. anacoluthon. Given its habitat requirements, many of the sites occur within upland, fast-flowing hill streams within wooded habitats, which are largely situated within country parks or protected areas (e.g., Tai Po Kau); however, those sites zoned 'Green Belt' under local planning guidelines are under pressure for housing developments (Authors pers. obs.). It should also be noted that the species does also occur at lower elevations, particularly in the western New Territories and on Lantau Island, where there are developmental pressures on lowland watercourses (see Appendix 2, Fig. 1).
Currently, there is no mechanism in place to protect the ecology of entire rivers and their catchments in Hong Kong (Dudgeon & Chan 1996;Cheung et al. 2010), and there is an urgent need for protection of the remaining rivers in their natural state (Hong Kong Birdwatching Society 2013); a similar situation is occurring in much of the rest of Asia (Cumberlidge et al. 2009(Cumberlidge et al. , 2010. When mitigation is prescribed through the EIA process in Hong Kong, it is usually in the form of watercourse preservation and the inclusion of riparian buffers and/or translocation exercises. Currently, there are no stringent guidelines for implementation of habitat management, riparian buffer zones or conducting species translocation (Stanton & Leven 2016). Projects for reducing habitat loss and fragmentation by watercourse restoration, recreation or enhancement and faunal conservation programs are being started or in progress (e.g., Cumberlidge et al. 2009Cumberlidge et al. , 2010Hong Kong Birdwatching Society 2015) in Hong Kong and elsewhere in the southern China region. The restricted range of many crab species from China, together with

Image 2. View of watercourses where Cryptopotamon anacoluthon occurs. A -Ma Yau Tong; B -Tei Lung Hau; C -Keung Shan
the ongoing human-induced loss of habitat in many parts of the region are a cause for concern, and it is considered that conservation activities should be aimed primarily at preserving the integrity of sites and habitats while closely monitoring key populations at the same time (Cumberlidge et al. 2010).
Many of the sites in Hong Kong are isolated, fragmented by a combination of developed areas (where downstream sections have been lost) and physical topography, and have few ecological linkages suitable for a predominantly aquatic species to exploit. Protection of known sites is therefore important, so that these can ensure the continued survival of the species, and suitable habitat management would also be beneficial either by providing increased habitat area or by providing corridors to link populations.

IUCN Red List Status
The present study is not intended to constitute a review of the IUCN listing of C. anacoluthon. Nevertheless, we suggest that the IUCN Red List of Threatened Species status of C. anacoluthon should be revisited in the light of our findings: it is most unlikely that the population size or its rate of decline and the extent of species occurrence or area of occupancy meet the IUCN criteria for the listing of C. anacoluthon as 'Vulnerable'. Conversely, the species is still known only from Hong Kong and probably with a relatively small, fragmented and declining population. Cumberlidge et al. (2010) stated that the existing IUCN Red List status can be updated by gathering current data on the distribution, natural history, population trends, threats, and endemism of China's highly diverse freshwater crabs. Once the IUCN Red List is updated, the conservation strategies can be developed for these understudied, diverse and potentially threatened fauna. It is hoped that the information gathered during the present study will help to feed into this process.

CONCLUSIONS
Cryptopotamon anacoluthon is widely distributed within Hong Kong; recorded throughout the New Territories, Hong Kong and Lantau Islands. So far, the species has not been recorded outside of Hong Kong. Generally, C. anacoluthon prefers fast flowing upland streams shaded by secondary woodland; however, the species has also been recorded in lower elevations from several locations, notably on Lantau Island and in the western New Territories. Watercourses in which this species occurs are largely natural with limited anthropogenic impacts such as channelisation or modification, but as the requirement of land increases for development, such areas will be under threat. Watercourse restoration projects provide an opportunity to conserve habitat of the species, and its habitat requirements should be taken into account when restoration measures are planned for potentially suitable watercourses.

Distribution of Cryptopotamon anacoluthon in Hong Kong
Stanton et al.