The controlling factor of mixotrophic haptophytes ingestion rate on bacteria in summer of the southern East China Sea

• Main Authors: Yao-Huei Wang, 王耀輝
• Other Authors: Chiang, Kuo-Ping
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/91944264891028992051

碩士 === 國立臺灣海洋大學 === 海洋環境化學與生態研究所 === 103 === 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).