UNDERSTANDING THE EFFECTS OF SEDIMENTS IN THE CORAL REEFS OF SINGAPORE � A MANAGEMENT PERSPECTIVE

Abstract

Coral reefs in Singapore have been subjected to high sedimentation levels brought about by anthropogenic activities such as reclamation and dredging. The resultant sediment-induced impacts can potentially cause the death and loss of coral reefs. As such, a one-year environmental monitoring study was conducted for three coral reef sites located in the southern islands of Singapore, to better understand the effects of sediments and related environmental parameters in the coral reefs of Singapore. General met-ocean conditions were obtained from secondary sources and DHI’s in-situ sensors in the Singapore Straits. During the monitoring, sediment traps and Odyssey PAR loggers were deployed at the reef crests and serviced monthly to ensure workability and allow for the collection of data. ¬In-situ water quality were monitored once every month during the monitoring period. Ecological coral reef data was recorded prior to the start of the monitoring. An additional experiment was conducted to (1) assess the composition of benthic reef sediment and accumulated sediment, (2) determine sedimentation rates across different reef locations, and (3) assess the rugosity or reef complexity of the three coral reef sites. Overall, monitoring results showed differences and similarities for the various environmental parameters across sites over the one year. Similarities were observed in sea surface temperatures, dissolved oxygen content, pH and salinities across the three monitoring sites. However, there were differences in current speed, current direction, sediment deposition rates, underwater PAR, turbidity, water transparency and light attenuation profiles across sites over the one year. In general, Big Sister’s Island and St John’s were influenced by strong tidal currents and ship wakes, high sediment deposition rates, underwater PAR, and water transparency which resulted in low turbidity readings and light attenuation values. Conversely, opposite results were recorded for Sultan Shoal. Differences in particle size composition were observed for the reef benthic sediments across sites but not for the accumulated sediment. There were no significant differences in sedimentation rates across reef locations. Rugosity values of the reefs showed that Big Sister’s Island and St John’s Island had higher reef surface complexity. Results showed complex interactions between sediment related parameters, yet these parameters supported the various ecological observations recorded within the reefs. The study of sediment effects in coral reefs is complex, but there lies opportunities to better understand sediment effects within coral reefs and incorporate them as part of the management decision making process in Singapore.