Introduction

Singapore is an island-nation that is situated at the southern tip of the Malay Peninsula.  The entire land area of the country is a mere 712.4 square kilometres but the country has a population of more than 5 million in 2010 (Singapore Census, 2010).  In the 1900s, the island was plagued with malaria as the vector, Anopheles sp. thrived in the tropical weather.  In order to tackle this problem, a drainage network was introduced in 1914 to transport seepage water and prevent stagnant water from pooling.  This initial network was made up of natural earth streams, subsoil pipes and concrete drains.  Another function of this network is to alleviate floods especially during the monsoon seasons which bring in more precipitation.  Two monsoons occur over a year, with the Northeast Monsoon bringing slightly more rain than the Southeast Monsoon.  Today, a vast network of more than 7000 kilometres of drain and canals reduce the possibility of floods occurring from more than 600 hectares in 1990 to less than 100 hectares in 2010.  Often these canals and drainage open either into reservoir or directly into the sea. 

Due to industrialisation, the initial 13% of forest and mangrove cover had dwindled to a dismal 0.5% of total land area.  In mangroves, crabs are the most abundant.  Crabs perform a myriad of activities including aerating the sediment by burrowing, changing topography and grain size distribution (Warren & Underwood, 1986), trap valuable energy within the mangrove forests (Robertson, 1986; Lee, 1998; Aston, 2002) and create essential microhabitat for other fauna (Bright and Hogue, 1972; Gillikin et al., 2001).  These organisms also contribute to secondary production (Lee, 1997) and through the flushing of sediment in their burrows (Ridd, 1996; Stieglitz et al., 2000) help reduce pore water salinity.  As a result of the quintessential role burrowing crabs play in the mangrove ecosystem, they may be considered to be a keystone species (Smith et al., 1991). 

A unique community of various species of crabs, mudskippers and monitor lizard had been discovered in the vicinity of an inland, open, concretised drain located within an urbanised area in Singapore.  The drain runs through open grassland connecting to a large storm drain which drains into the sea some three kilometres away.  While crab communities are known to be well-established in Singapore’s beaches and remaining mangroves like Pasir Ris Park and East Coast Park (Fig. 1), little has been documented about similar communities thriving in urbanised inland areas.  Hence the objective of this study is to determine if the abiotic conditions like salinity, sediment particle size and physiological responses of the crabs in the drain were any different from similar species found in their natural habitats and to document its unique mix of fauna found.