Nutrient diagenesis in sediments of the South China Sea, Area II: Sabah, Sarawak, and Brunei Darussalam waters

Study on nutrient diagenesis and physico-chemical characteristics of bottom sediments of the Sabah, Sarawak and Brunei Darussalam waters had been carried out under the ongoing SEAFDEC Collaborative Research Project. The results indicated that organically enriched offshore sediments consisted high levels of pore water nitrate and phosphate concentrations. For the whole study area, the levels of nitrate and phosphate concentrations in pore water were in the ranges of 0.05 to 77.12 µg at NO3--N/L and 0.07 to 13.13 µg at PO43--P/L, respectively. Upward diffusive fluxes of pore water nitrate widely changed in stations. At the nearshore area, the fluxes of pore water nitrate had an average of 26.5 mg at NO3--N/m2/d and were about one order of magnitude higher than those of phopsphate. However, phosphate upward fluxes were apparently high at deep areas off Sabah. Pore water ammonium concentrations were commonly very low but tended to be more accumulated at nearshore organically enriched areas. The ammonium concentrations for the whole study area ranged from non-detected level to 81.76 µg at N/L. The nearshore stations showed very high upward fluxes of ammonium, which were nearly 10 times higher than those of nitrate and phosphate. Sedimentary organic levels were comparatively high in two distinct regions; (I) a shallow nearshore region of Sarawak, and (II) a deep offshore region of Sabah and Brunei Darussalam. The sources of organic materials settled in Regions (I) and (II) were suggested to be derived from different origins. The Northeast monsoon can somewhat enhance organic accumulation in the nearshore region. Overall our results obtained from this study had been used to characterize the bottom sediments into three distinct regions and discussed for further fishery resource development and management

Seasonal variations in cell abundance of Noctiluca scintillans in the coastal waters off Chonburi Province, the upper Gulf of Thailand

Seasonal variations in cell abundance of Noctiluca scintillans was studied from June 2003 to November 2004 in the coastal waters off Chonburi Province, the upper gulf of Thailand. Eight stations from Bangpakong River mouth to Angsila were designed to cover the area where red tides often occurred and were under the influence of Bangpakong River. Numerical abundance was analyzed in relation with some environmental parameters. A total of 9 N. scintillans red tides, 7 Ceratium furca red tides and 4 diatom red tides were found in this study. Noctiluca and Ceratium red tides were often found when salinity was in the range of 22 to 33psu. and 12 to 27psu., respectively. Those red tides were not associated with apparent negative effects to marine animals. N. scintillans cells could be observed almost all year round at offshore stations where the water depth was more than 10 meters except strong wind periods, suggesting that Noctiluca in coastal waters were supplied by cells from offshore stations. In contrast, no consistent pattern was observed in the distribution of N. scintillans in coastal waters, in particular near the river mouth. Only the relationship between phosphate concentrations and cell densities of Noctiluca has been found statistically significant. However, the high cell densities of both Noctiluca and Ceratium were often observed in the rainy season, especially on the calm day after heavy rain. These observations suggested that the red tides of those two species in coastal waters were growth response to the influence of freshwater run off from Bangpakong River

Effects of Temperature on the Germination of Marine Phytoflagellate Cysts

The effect of temperature on the germination of some phytoflagellate cysts was studied in two different temperature conditions, step-gradient temperature and constant temperature. The highest number of newly germinated cell of Scrippsiella spp., Alexandrium spp., Protoperidinium spp., Gyrodinium spp., Gymnodinium spp., and Diplopelta spp. was observed after incubation 2 or 3 days when the initial temperatures were 13 and/or 19 ℃, but it took at least 5 days at the initial incubation temperature of 10 ℃. The germination rates of phytoflagellate cyst under optimum window should be faster than the other temperature ranges. The optimum temperature for cyst germination of Alexandrium spp., Protoperidinium pellucidum Bergh and Protoperidinium spp. was considered to be at 16 ℃. For Scrippsiella spp., Gymnodinium spp. (small) and Gymnodinium spp., the optimum temperature for their cyst germination was considered to be 13 ℃, whereas that for Chattonella spp. could be as high as 25 ℃

Nutrient Diagenesis in Sediments of the South China Sea, Area II: Sabah, Sarawak, and Brunei Darussalam Waters

Study on nutrient diagenesis and physico-chemical characteristics of bottom sediments of the Sabah, Sarawak and Brunei Darussalum waters had been carried out under the ongoing SEAFDEC Collaborative Research Project. The results indicated that organically enriched offshore sediments consisted high levels of pore water nitrate and phosphate concentrations. For the whole study area, the levels of nitrate and phopsphate concentrations in pore water were in the ranges of 0.05 to 77.12 ?g at NO3--N/L and 0.07 to 13.13 ?g at PO43--P/L, respectively. Upward diffusive fluxes of pore water nitrate widely changed in stations. At the nearshore area, the fluxes of pore water nitrate had an average of 26.5 mg at NO3--N/m2/d and were about one order of magnitude higher than those of phopsphate. However, phosphate upward fluxes were apparently high at deep areas off Sabah. Pore water ammonium concentrations were commonly very low but tended to be more accumulated at nearshore organically enriched areas. The ammonium concentrations for the whole study area ranged from non-detected level to 81.76 ?g at N/L. The nearshore stations showed very high upward fluxes of ammonium, which were nearly 10 times higher than those of nitrate and phosphate. Sedimentary organic levels were comparatively high in two distinct regions; (I) a shallow nearshore region of Sarawak, and (II) a deep offshore region of Sabah amd Brunei Darussalum. The sources of organic materials settled in Regions (I) and (II) were suggested to be derived from different origins. The Northeast monsoon can somewhat enhance organic accumulation in the nearshore region. Overall our results obtained from this study had been used to characterize the bottom sediments into three distinct regions and discussed for further fishery resource development and management

Seasonal variations in cell abundance of Noctiluca scintillans in the coastal waters off Chonburi Province, the upper Gulf of Thailand

Seasonal variations in cell abundance of Noctiluca scintillans was studied from June 2003 to November 2004 in the coastal waters off Chonburi Province, the upper gulf of Thailand. Eight stations from Bangpakong River mouth to Angsila were designed to cover the area where red tides often occurred and were under the influence of Bangpakong River. Numerical abundance was analyzed in relation with some environmental parameters. A total of 9 N. scintillans red tides, 7 Ceratium furca red tides and 4 diatom red tides were found in this study. Noctiluca and Ceratium red tides were often found when salinity was in the range of 22 to 33psu. and 12 to 27psu., respectively. Those red tides were not associated with apparent negative effects to marine animals. N. scintillans cells could be observed almost all year round at offshore stations where the water depth was more than 10 meters except strong wind periods, suggesting that Noctiluca in coastal waters were supplied by cells from offshore stations. In contrast, no consistent pattern was observed in the distribution of N. scintillans in coastal waters, in particular near the river mouth. Only the relationship between phosphate concentrations and cell densities of Noctiluca has been found statistically significant. However, the high cell densities of both Noctiluca and Ceratium were often observed in the rainy season, especially on the calm day after heavy rain. These observations suggested that the red tides of those two species in coastal waters were growth response to the influence of freshwater run off from Bangpakong River