The Mangrove Ecosystem of Deep Bay and the Mai Po Marshes, Hong Kong

The brachyuran fauna of the Mai Po Marshes Nature Reserve and Deep Bay, Hong Kong

The Mangrove Ecosystem ofDeep Bay and the Mai Po Marshes, Hong Kong (ed. S.Y. Lee). Proceedings of the International Workshop on the Mangrove Ecosystem of Deep Bay and the Mai Po Marshes, Hong Kong, 3-20 September 1993. Hong Kong: Hong Kong University Press, 1999. THE BRACHYURAN FAUNA OF THE MAl PO MARSHES NATURE RESERVE AND DEEP BAY, HONG KONG s.y. Lee* Department of Ecology & Biodiversity and The Swire Institute of Marine Science, The University of Hong Kong, Pokfulam Road, Hong Kong and v. Leung Edi~ao da Camara Municipal das Ilhas, Macau ABSTRACT A survey was conducted on the brachyuran fauna of the Mai Po Marshes and Deep Bay in September 1993. Thirty-two species, dominated by Grapsidae (13 species) and Ocypodidae (18 species) were recorded from the intertidal and semi-terrestrial habitats at the Mai Po Marshes, while only 14 species from four families were collected from the trawl survey of the sub-tidal areas in Deep Bay. There is a distinct underrepresentation of the semi-terrestrial component of the brachyuran fauna compared to assemblages characteristic of the region. This reduced species richness is probably a result of the modification of the supra-littoral habitats at Mai Po into aquaculture ponds, destroying much of the high-shore sesarmines. Different and non-overlapping assemblages of crabs dominated in the various habitats. Species richness was low in Deep Bay compared to other surveyed Hong Kong waters. Although the deep waters of Urmston Road housed the highest diversity among the stations, no distinct species groups could be identified for the various parts of Deep Bay. A brief description is given for selected species recorded in the survey. * Present address: School of Environmental and Applied Science, Faculty of Environmental Sciences, Griffith University Gold Coast, PMB50 Gold Coast Mail Centre, Qld 9726, Australia 57 58 S.Y.LEE & V. LEUNG INTRODUCTION Situated at about 300 km south of the Tropic of Cancer, Hong Kong (22°N 114°E) has a generally diverse fauna with species of both tropical and temperate origins present in the territory. This high diversity is well exemplified by Brachyura, as a rough estimate suggests an overall species richness of > 300, with Portunidae, Grapsidae and Ocypodidae being important families each contributing> 20 species (Lee, unpubl. data; Lee at a!., in press). Dai et al. (1991) described a total of > 800 species of marine bracyhurans from the Chinese seas. With a land area of just :::::1078 km2 but a coastline considerably extended by drowned river valleys, Hong Kong contributes about 25% of the overall Chinese Brachyura fauna. The high diversity of Hong Kong's brachyuran community has also been suggested by the earlier works of Shen (1931a; b; 1932; 1934; 1940). The checklist of Shen (1940) documented a total of 187 species. This large number of species was the result of collection mostly from only a few locations in the territory, many of which have now been destroyed by development in the last few decades, e.g. the mangroves and mudflats around Tai Po and Shatin have been developed into two new towns now housing more than one million people. Since the early work of Shen, most recent works on Hong Kong's brachyuran fauna focused on specific groups, e.g. Sesarminae (Soh 1978; Lee et al. in press) and Leucosiidae (Hill 1982), or particular geographic areas, e.g. Tolo Harbour and Channel (Cheung 1990; Davie 1992a; Lam 1992). Although only partial pictures of the overall fauna, these reports all support the high species richness as well as ecological importance of Brachyura first documented by Shen (1940) more than half a century ago. For example, Lee et al. (in press) reported upon 15 species of Sesarma senu lato from Hong Kong while Cheung (1990) recorded abundance at> 110 individuals and dry biomass at 26.5 g of Portunus hastatoides (probably P. trilobatus, Davie 1992a) per pair trawls of 10-minute total duration in inner Tolo Harbour. The coastal areas of Hong Kong are increasingly threatened by pollution, reclamation and development (Morton et al. 1996). Alteration of the physical environment of habitats inevitably jeopardises their fauna. Lee et al. (in press) attributed the generally low representation of the high intertidal, semi-terrestrial species of local Sesarminae, e.g. Chasmagnathes convexus, to the widespread in-filling and development of their habitats in the territory. Similarly, large scale dredging for marine sand in the eastern waters areas during 1992-95, strong disturbances to the brachyuran assemblage probably resulted in that time. The Mai...