Ecological role of nanozooplankton in the heterotrophic cycle in the Ocean

研究了纳米浮游动物在海洋有机质异养循环中的作用。纳米浮游动物由于体积小且无色，很难通过光学显微镜发现。电子显微镜对这些生物的分类是一种有用的方法，但它耗时且不能进行定量估计。本课题研制了植物、动物、浮游细菌的荧光染色显微镜。该方法简便、快速，对这些生物的分类和定量观察都是最有效的。在南冰洋，纳米浮游动物的丰度随浮游生物总量（包括浮游植物）的细胞体积变化从0%到25%（平均7%）不等。对南极生态系统的关键物种南极磷虾（Euphausia superba）粪便颗粒的有机分析和电镜检查表明，南极磷虾以南极海洋中丰富的纳米浮游动物——尾鞭毛虫为食。提出了南极生态系统有机物质的新途径；一个新的食物链，包括无生命颗粒和溶解有机物质和细菌-鞭毛-磷虾-脊椎动物，以及传统的无机营养物-硅藻-磷虾-脊椎动物的食物链。纳米浮游动物，尤其是鞭藻和变形虫，在北太平洋北部和白令海中也很常见和丰富。本研究认为，这些纳米浮游动物在海洋食物链中起着连接非生命细菌水平和浮游动物-脊椎动物水平的中间环节的重要作用。

Role of nanozooplankton was investigated in relation to the heterotrophic cycle of organic matter in the Ocean. Nanozooplankters have been hard to find by light microscopy because of its small size and colourlessness. Electron microscopy has been a useful method for taxonomy of these organisms, but is time consuming and is not acculate in quantitative estimation. In the present project, a fluorescent dye staining epifluorescence microscopy of phyto-, zoo-, bactrioplankton was developed. this method was easy and rapid for sample preparation on board and was proved most effective for both taxonomic and quantitative observations of these organisms.In the Antarctic Ocean, the abundance of the nanozooplankton was varied from 0% to 25% (7% on average) by cell volume in total plankton, including phytoplankton. Organic analyses and electron microscopic examination on fecal pellets produced by the Antarctic krill, Euphausia superba, the key species of the Antarctic ecosystems, showed that the krill fed on choanoflagellates, the abundant member of the nanozooplankton in the Antarctic Ocean. Thus, a new pathway of organic materials in the Antarctic ecosystem is proposed; a new food chain including nonliving particulate and dissolved organic materials and bacteria-choanoflagellates-krill-vertebrates, as well as traditional inorganic nutrients-diatoms-krill-vertibrates food chain.Nanozooplankton, especially choanoflagellates and amoebae, were also common and abundant in the northern North pacific and the Bering Sea.It was concluded in the present project that these nanozooplankters play an important role as an intermdeiate link which couples nonliving-bacteria level with net-zooplankton-vertibrate level in the marine food chain.