Distribution of dinoflagellate cysts in the surface sediment of South China Sea: Area 2. Off Sabah, Sarawak and Brunei Darussalam

The surface sediment samples of 47 stations in Sabah, Sarawak and Brunei Darussalam waters were collected by M.V. SEAFDEC for identification and quantitative analysis of benthic dinoflagellate cysts. A total of 18 dinoflagellate cyst belonging to family Gonyaulacaceae, Pyrophacaceae and Protoperiniaceae were identified. The cyst density in this area was in a range of 6 to 278 cysts/cm3 with Spiniferites bulloideus was the dominant species. Cysts of harmful species were not observed in this study but a small number of Alexandrium cyst-like was found at a station near coastal area of Sarawak

夏季タイ湾奥部表層におけるヤコウチュウの分布

Distribution of Noctiluca scintillans, nutrients and chlorophyll a at the surface was investigated in the upper Gulf of Thailand in summer. Observation was made along two longitudinal lines across the inner gulf during the southwest monsoon period. Significantly high chlorophyll a was observed at stations on the northern line compared to the southern line, and the highest abundance was located in the eastern part of the line. This was accompanied by significantly elevated nitrate in the eastern part. Higher abundance of N. scintillans cells was observed also along the northern line, and its maximum occurred in the eastern part. The high abundance of both chlorophyll a and N. scintillans in the northeastern part of the study area supports Sriwoon et al. (2008) who showed a build-up of N. scintillans and phytoplankton biomass in the northeastern part of the upper gulf, where surface water circulation alters according to the monsoon cycle: the southwest monsoon induces a clockwise circulation from the west to theeast, and the northeast monsoon develops a counterclockwise circulation. Sriwoon et al (2008)concluded that the southwest monsoon circulation produces a favorable condition for growth ofN. scintillans in the northeast part of the upper gulf. In the present study a significant correlationwas found among nitrate, chlorophyll a and abundance of N. scintillans, suggesting phytoplanktonabundance supported by high nitrate availability served as prey for N. scintillans. This inferenceis compatible with findings of Sriwoon et al. (2008)

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

Distribution of Dinoflagellate Cysts in the Surface Sediment of the South China Sea, Area I: Gulf of Thailand and East Coast of Peninsular Malaysia

To obtain more information on the distribution of dinoflagellate cysts in Thai and Malaysian waters, the surface sediment samples of 48 stations in the Gulf of Thailand and the east coast of Peninsular Malaysia were collected by M.V. SEAFDEC during the research cruise in September 1995 and repeated again in April 1996. Cysts of 20 species belonging to Goniolacoid, Tuberculodinioid and Peridinioid were found in the surface sediments collected from both cruises. Spiniferites spp. (=Gonyaulax spp.) were the dominant cyst in Thai and Malaysian waters. No cysts of harmful species were observed during this study

Distribution of dinoflagellate cysts in the surface sediment of the coastal areas in Chonburi Province, Thailand

Distribution of dinoflagellate cysts were investigated in rainy and dry seasons in the surface sediment of the coastal areas in Ang-sila, Bang-pra, Si-racha and Laem-chabang, Chonburi Province, Thailand. Sampling cruises were conducted in February and September 2005 that were during the dry and rainy seasons, respectively. Thirty types of cysts were found of which 28 cysts belonged to the orders Gonyaulacales, Gymnodiniales and Peridiniales and two were of unknown cyst types. The dominant species were Pheopolykrikos hartmannii and Pyrophacus steinii and the most common species were P. hartmannii, Gonyaulax spinifera (Spiniferites mirabilis), Lingulodinium polyedrum, P. steinii, Protoperidinium pentagonum and P. leonis. Dinoflagellate cysts were widely found in most stations of the study area. The total numbers of dinoflagellate cysts in dry season were higher than those in rainy season. The abundance of dinoflagellate cysts in both seasons was higher at the stations deeper than 10 meter around Ang-sila and Bang-pra areas than at the stations near Laem-chabang areas. These findings suggest that cyst abundance and distribution might be affected by seasonal changes of environment and fishery activity.Proceedings of the Horiba International Conference "New Direction of Ocean Research in the Western Pacific" : Past, Present and Future of UNESCO/IOC/WESTPAC Activity for 50 years and the JSPS Project "Coastal Marine Science"Section I: Research Articles/Harmful microalga

Distribution of dinoflagellate cysts in the surface sediment of the coastal areas in Chonburi Province, Thailand

Distribution of dinoflagellate cysts were investigated in rainy and dry seasons in the surface sediment of the coastal areas in Ang-sila, Bang-pra, Si-racha and Laem-chabang, Chonburi Province, Thailand. Sampling cruises were conducted in February and September 2005 that were during the dry and rainy seasons, respectively. Thirty types of cysts were found of which 28 cysts belonged to the orders Gonyaulacales, Gymnodiniales and Peridiniales and two were of unknown cyst types. The dominant species were Pheopolykrikos hartmannii and Pyrophacus steinii and the most common species were P. hartmannii, Gonyaulax spinifera (Spiniferites mirabilis), Lingulodinium polyedrum, P. steinii, Protoperidinium pentagonum and P. leonis. Dinoflagellate cysts were widely found in most stations of the study area. The total numbers of dinoflagellate cysts in dry season were higher than those in rainy season. The abundance of dinoflagellate cysts in both seasons was higher at the stations deeper than 10 meter around Ang-sila and Bang-pra areas than at the stations near Laem-chabang areas. These findings suggest that cyst abundance and distribution might be affected by seasonal changes of environment and fishery activity.Proceedings of the Horiba International Conference "New Direction of Ocean Research in the Western Pacific" : Past, Present and Future of UNESCO/IOC/WESTPAC Activity for 50 years and the JSPS Project "Coastal Marine Science"Section I: Research Articles/Harmful microalga

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