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The controlling factor of mixotrophic haptophytes ingestion rate on bacteria in summer of the southern East China Sea
|Authors: ||Yao-Huei Wang|
|Issue Date: ||2017-11-15T08:45:42Z
|Abstract: ||微細鞭毛蟲為單細胞真核生物，大小介於2-20 μm。其中混營性鞭毛蟲(mixotrophic nanoflgellates)族群在某些海域數量較為優勢，且對海洋環境中之細菌數量有一定的控制。東海南部海域由馬祖到黑潮測線，沿岸到外海有自然形成的鹽度梯度，在並受湧昇流之影響，因此在整條測線營養鹽會有非常明顯的變化，本研究希望了解營養鹽變化下，對著鞭毛蟲攝食率有何影響。本次研究在2014年7、8、9月東海南部海域，使用海研二號(OR2- cr2039、cr2046、cr2053)進行三個航次的調查。使用聯酶螢光原位雜合法(tyramide signal amplification-Fluorescence in situ hybridization, TSA-FISH)來標識所要觀察的著鞭毛蟲。並針對有光層表層(SE)及底層(BE)中著鞭毛蟲進行攝食細菌之培養實驗。 以T-S diagram圖顯示，夏季的東海南部海域以台灣暖流水水團為主。細菌現存量約為3-16 x105 cells ml-1，SE與BE之數量經檢定並沒有差異。總微細鞭毛蟲數量大約1592.67 cells ml-1，而色素型鞭毛蟲數量較異營性微細鞭毛蟲多，平均約為1112 cells ml-1。其中著鞭毛蟲在SE之平均數量440 cells ml-1，在BE為 202 cells ml-1；整體平均為321 cells ml-1。大約佔色素型微細鞭毛蟲29.7 %。以體型大小分三個族群( < 3 μm、3-5 μm及> 5 μm)，其中以中型之著鞭毛蟲(3-5 μm)佔最多量，約53 %。著鞭毛蟲之個體攝食速率在SE約28.02 bac Hap-1 mL-1。在BE，其攝食率約為41.74 bac Hap-1 mL-1。平均約可移除細菌現存量1.56 %。結果顯示，表底層攝食率經檢定後均沒有差異(t-test, p > 0.05)。SE及BE攝食率分開與環境因子進行相關性分析，發現僅BE攝食率與細菌關係良好性(p < 0.05)。 再次證實混營性著鞭毛蟲攝食不會受到光線影響。其次本海域夏季實際上大部分受貧營養鹽之台灣暖流水水團所覆蓋，營養鹽NO3濃度大多< 1 μm，並無明顯營養鹽梯度存在。因此著鞭毛蟲無法發現與營養鹽等環境因子有密切的關係。並且在現場細菌數量< 6×105 cells mL-1時，餌料濃度不足，攝食率集中在一個範圍變動。而> 6×105 cells mL-1時，餌料濃度充足，其攝食率明顯增加。|
Nanoflagellates, 2-20 μm in size, are unicellular eukaryotes. The mixotrophic nanoflgellates are dominant among nanoflagellates and control the abundance of marine bacteria by grazing in some pelagic environments. It has been confirmed that haptophytes are most important bacterivory among the mixotrophic nanoflgellates. In this study, our stations were located on a line stretching from Matsu to the Kuroshio in southern East China Sea, witha salinity gradient from coast to offshore andwith clear nutrient change due to upwelling. The purpose of this study was to find out the impact of haptophyte ingestion rates on bacteria under different nutrient concentrations. We conducted the experiments in three cruises (OR2- cr2039, cr2046, cr2053) during July, August and September in the southern East China Sea, using tyramide signal amplification-Fluorescence in situ hybridization (TSA-FISH) to identify the specific flagellates (haptophytes). The grazing experiments were performed in surface (SE) and bottom (BE) euphotic zones in this study. From the T-S diagram, the Taiwan Warm Current is the main water mass in the southern East China Sea. The abundance of bacteria in this area was about 3-16 x105 cells ml-1. There was no significant difference in the bacteria abundance between SE and BE. Thrtotal nanoflgellates abundance was approximately 1592.67 cell ml-1. The abundance of pigmented nanoflgellates (1112 cell ml-1) was higher than that of heterotrophic nanoflgellates. The haptophyte abundance was about 440 cell ml-1 and 202 cell ml-1 in SE and BE, respectively. The average haptophytes abundance was 321 cell ml-1 which was 29.7 % of the total pigmented nanoflgellates. The medium cell sized haptophytes were the most abundant (53 %) and were divided into three cell size categories (< 3 μm, 3-5 μm and > 5 μm). The haptophyte ingestion rates were approximately 28.02 bac Hap-1 mL-1 and 41.74 bac Hap-1 mL-1 in SE and BE, respectively. In average haptophytes removed 1.56 % of the bacteria abundance. There was no significant difference in the haptophyte ingestion rates between SE and BE (t-test, p > 0.05). The ingestion rates were positively correlated with bacteria abundance in BE. We confirmed that the ingestion rates of mixotrophic nanoflgellates was not affected by light intensity. There was no apparent nutrient gradient in the waters surveyed by our cruises. Therefore, there was no clear relationship between the haptophyte ingestion rates and nutrient concentration. Furthermore, the haptophyte ingestion rates were not changed distinctly when the abundance of bacteria was less than 6×105 cells mL-1. The haptophyte ingestion rates increased significantly when the prey concentration was sufficient (> 6×105 cells mL-1).
|Appears in Collections:||[海洋環境與生態研究所] 博碩士論文|
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