การแปรผันของความชุกชุมและมวลชีวภาพในรอบปีของพิโคแพลงก์ตอนบริเวณป่าชายเลน บ้านคลองโคน จังหวัดสมุทรสงคราม / วรพร ธารางกูร = Annual variations in abundance and biomass of picoplankton in Klong Kone Mangrove Swamp, Samut Songkhram Province / Woraporn Tarangkoon
Variations in density and biomass of picoplankton in mangrove creek at Baan Klong Kone, Samut Songkhram were studied from May 2001 to April 2002. Subsurface water samples were collected in triplicates at four different sites along, Klong Praek Yai in the mangrove forest at daytime stagnant – high tide. Physico-chemical parameters were measured in situ prior to water samplings. Extracted chlorophyll a as well as cellular organic carbon and nitrogen were analyzed from size fractionated samples. Concentrations of dissolve nutrients were also determined from prefiltered seawater except for ammonium nitrogen. Density of picoplankton was determined from samples preserved in glutaraldehyde and dyed with Proflavin fluorescent dye. Enumeration of picoplankton was conducted under the epifluorescence microscope with blue excitation and later confirmed under by UV and green excitation. Picoplankton found in this study was categorized into 3 major groups based upon the cell size and shape as well as the fluorescence color schemes. First group was heterotrophic picoplankton, the second group was phototrophic picoplankton comprised of picocyanobacteria and phototrophic picoeukaryotes, and the third group was unidentified picoeukaryotes. Heterotrophic picoplankton was the most abundant picoplankton with the maximum density of 1.84x106 cells/ml in rainy season of September. The minimum density of heterotrophic picoplankton, 9.60x105 cells/ml, found in the period of early rainy season (June). Density of phototrophic picoplankton, dominated by picocyanobacteria varied between 6.36x104 and 2.18x105 cells/ml during the dry season (December) and early rainy season (May). Phototrophic picoplankton biomass as determined in form of chlorophyll a biomass ranged from 2.280 to 22.605 mg/m3 with the highest concentration in the rainy season (July) and the lowest one in the dry season (January). The fractionated chlorophyll a of phototrophic picoplankton was only 7.88% of total chlorophyll a in the creek. The major producer in the water column of Klong Kone mangrove was nanophytoplankton whose relative contribution of total chlorophyll a was about 84.41% while microphytoplankton chlorophyll a was only 7.71% relatively to the total concentrations. The C:N ratio of phytoplankton was about 3.9 which is smaller than Redfield C:N ratio. Therefore, Klong Kone mangrove swamp was enriched with organic nitrogen that may supported the high density of heterotrophic picoplankton. There was no spatial variation in the biomass and abundance of picoplankton along Klong Kone mangrove creek, however, temporal variations were observed. These variations were under the influence of dissolved nutrients and also depended on some physical parameters. Besides, the indirect enhanced bacterial production due to the release of dissolved organic matter and the grazing pressure from bacteriovore zooplanktons are also suspected to play important roles in controlling the abundance and distribution of picoplankton in Klong Kone mangrove creek on temporal basis. This study also indicated the importance of food web started from picoplankton as well as nanoplankton and microbial loop on the process of material and energy transfers in this pelagic phase of Klong Kone mangrove forest.