Investigation of Freshwater Crab Habitat Characteristics within Nee Soon Swamp Forest

Abstract

Singapore’s only remaining swamp forest, Nee Soon Swamp Forest, is home to three species of freshwater crabs – two of which are endemic and endangered. Although they are recognised as vulnerable to environmental changes and pollution, little is known about these crabs’ habitat requirements and the threats they face. This thesis has filled that gap by investigating the hydrological, hydrochemical, and sediment geochemical characteristics of 45 freshwater stream habitats. Crabs were trapped and counted, while water and sediment samples were tested for general quality parameters, naturally-occurring ions, and heavy metals. Crabs were found in shallow, slow, acidic and poorly-oxygenated streams with sediment beds high in organic carbon. Habitat hydrology was found to be the greatest factor of crab abundance. Hydrochemical pollutants such as nitrites and heavy metals were either in low concentrations or below detection limits. The sediments were deemed as potential pollutants, 30 sites had toxic levels of at least one heavy metal – particularly copper, iron and lead. However, there were no significant correlations between the sediment metal concentrations and crab abundance, indicating that the polluted sediments were not acutely toxic to crabs. Comparing this study’s results with other studies revealed that potential long-term bioaccumulation of metals is a concern in NSSF crabs. Further research into metals bioavailability, bioaccumulation and species-specific toxicity is recommended for better monitoring and management of the crabs and their habitats.