Studies on non-dominancy of large diatoms and the mechanism for maintaining their populations in the pelagic ocean

在过去3年的研究中，在中西太平洋从50ﾟN到65ﾟS的大范围内进行了野外观测和采样。在中太平洋，3-5年在同一季节多次重复观测，并在同一地区的不同季节进行观测。细胞或菌落长度为100微米的大型硅藻物种特别受关注，因为它们容易被自然群落识别。在整个研究区内发现了几种到几十种大型硅藻，这表明大型硅藻的分布范围很广。在整个研究区内没有分布任何种类，但有一些种类分布在1000多公里的范围内，也有一些种类分布在100公里以内。其分布可分为6-8个类型。在高纬度地区，每种硅藻的数量丰度都达到了几个百分点，但在其他地区，硅藻的数量丰度在10^&lt；-4；由于每种硅藻的生物量都很大，在高纬度地区生物量的占有率较大，达到50%以上，而在其他地区的生物量只占10%~2%。通过本研究，确定了大型硅藻可能以非优势状态出现的海域和季节。这给了我们一个研究海洋中物种的非恶魔的承诺。

During the past 3 years of research, field observations and samplings were carried out covering a large area from 50ﾟN to 65ﾟS in the central and western Pacific Ocean. In the central Pacific, repeated observations in a same period of season were made several times during 3 to 5 years as well as making observations in different seasons in the same area. Large diatom species of >100um in length of cell or colony were particularly concerned because of their easy recognition from natural community. Several to a few 10 species of large diatoms were always found in the entire study area, which demonstrated a wide generous distribution of the large diatoms. No species was distributed throuout the study area but some species occurred in the area of over few 1000km and some others were within a few 100km. The distribution was grouped in 6-8 types. Numerical abundances of each diatom species reached a few % in high latitudes but they were <10^<-4> in the rest of areas. Due to a large biomass of each diatom species, dominancy of biomass became fairly large reaching over 50% at high latitudes, but they were <10^<-2> in the rest of areas. From the present study, ocean areas and seasons where the large diatoms possibly occurred in non-dominance were identified. This has given us a promise to study non-demonancy of species in the ocean.