Search

This monitoring study encompassed a period prior to dredging, during dredging and post dredging between July 1999 to June 2000 in Ponggol estuary located along the northeastern coast of Singapore. Mean concentrations of sediment nutrients in mg ⋅ Kg−1 (± standard error of means) prior to dredging, during dredging and post dredging were 9.75 ± 4.24, 8.18 ± 4.29 and 11.46 ± 4.74 for ammonium, 0.08 ± 0.05, 0.06 ± 0.02 and 0.09 ± 0.01 for nitrite, 0.04 ± 0.04, 0.11 ± 0.17 and 0.25 ± 0.30 for nitrate, 4.83 ± 3.48, 0.77 ± 0.48 and 8.33 ± 9.73 for phosphate respectively. Pre dredge, dredge and post dredge levels of total carbon (TC) were 18.5 ± 3.7, 20.2 ± 3.5 and 34.6 ± 12.0, of total organic carbon (TOC) were 10.5 ± 2.9, 19.5 ± 3.6 and 34.6 ± 12.0 and of total inorganic carbon (TIC) were 7.9 ± 1.0, 0.7 ± 0.4 and non detectable in the sediments, respectively. Both, sediment nutrients and carbon registered lower concentrations with onset of dredging, with the exception of nitrate and TOC. A shift in sedimentary carbon from inorganic carbon to organic carbon was also observed with the onset of the dredging activities when the organically enriched historically contaminated layer was exposed. Sediment granulometry showed that the sediments in the estuary were predominantly silt and clay prior to dredging, which changed to sand with onset of dredging. Silt load in the sediments was highest post-dredge. Sediment nutrients and sediment organic carbon were observed to associate with the finer fractions (silt and clay) of sediments. Finer fractions of sediments get resuspended during a dredging event and are dispersed spatially as the result of tides and water movements. Prior to this study, the potential for nutrient release and sediment granulometry due to dredging have been suggested, but there have been few studies of it, especially in the tropics. The baseline information gathered from this study could be used to work out effective management strategies to protect similar tropical ecosystems elsewhere, should there be no other alternative to dredging. [ABSTRACT FROM AUTHOR]

The rates of oxygen production and respiration of the colonial zoanthid of the genus Palythoa were measured in situ at a depth of 3.4 m (reef-edge) using an automated respirometer. The respirometer recordedchanges in oxygen concentration of four samples of Palythoa enclosedin separate perspex chambers concurrently with light intensity (irradiance) readings every 20 seconds for 24 hours. Photosynthetic parameters (Pm(gross), Rd and Ik) were estimated from photosynthesis--irradiance (PI) curves generated for each of the four samples. Average instantaneous maximum gross photosynthetic (Pm(gross)) and respiration (Rd) rates obtained for Palythoa were 12.50 mu mol O2 cm- 2 h-1 and 4.24 mu mol O2 cm-2 h-1, giving a Pm(gross)/(-Rd) ratio of 2.92. The net 24 hour production (Pn24) at 3.4 m, estimated by integrating the photokinetic parameters over 7 days of light data, was negative, resulting in a daily gross photosynthesis to respiration [Pg24/(-Rd24)] ratio of 0.77, while estimated 24 hour productivity at 1.4 m gave a ratio of 1.13. This suggests that Palythoa would be able to sustain positive production at 1.4 m but not at 3.4 m. [ABSTRACT FROM AUTHOR]

Spatial distribution of the pomacentrids on Singapore reefs was assessed visually, while temporal change was studied within permanent quadrats established on a patch reef between 4 Jul and 30 Nov 1989. Partitioning of space, both horizontally and vertically on the reef was observed in 15 species The population of territorial damselfishes on the reef flat was less stable than on the reef slope over time, due tothe seasonal occurrence of dense stands of the brown microalgae, Sargassum. Space was found to be a limiting factor at the reef flat due to the high density of pomacentrids found there. Food resource was the limiting factor on the reef slope., where low light intensity due to sedimentation and lack of suitable substrate inhibited turf algal growth. Multi-specific recruitment of juveniles occurred in April and between mid-October and early November. [ABSTRACT FROM AUTHOR]

Artificial reefs are seen as effective tools to enhance the marine environment and increase productivity, particularly fish biomass and abundance. Many Southeast Asian countries have implemented artificial reef programmes. When effectively managed, artificial reefs enhance habitats and biological productivity. Management includes proper planning on the use and configuration of materials, site selection, and regulatory control of fisheries harvest. Without planning and long-termmanagement, artificial reefs fail and become nothing more than pollutants that contribute to the further degradation of the marine environment. [ABSTRACT FROM AUTHOR]

Zonation patterns of gorgonians from 15 sites on reefs south of the main island of Singapore reveal discontinuities in terms of both generic richness and total abundance. This establishes the crest, slope, and bottom as ecologically distinct environments of the reef, as interpreted by these gorgonian population parameters. Only members of thefamily Melithaeidae are able to colonise all three zones. Other genera are restricted to the slope and bottom; in particular, Aconthogorgia and Echinoinuricea are only found at the bottom zone. [ABSTRACT FROM AUTHOR]