Horizontal distribution of microprotist community structure in the western Arctic Ocean during late summer and early fall of 2010

The western Arctic Ocean is composed of two regions: the southern shelf and the northern basin, whereas the marine ecosystem structure is expected to vary between the regions, little information is available, particularly for the planktonic protist community. In this study, we surveyed the horizontal distribution of microprotists (diatoms, dinoflagellates and ciliates) at 59 stations in the western Arctic Ocean during September and October of 2010. The abundances of diatoms, dinoflagellates and ciliates were 0-138,640, 0-16,460 and 0-10,933 cells L-1, respectively, and all of the abundances were higher on the Chukchi Sea shelf. Cluster analysis based on abundance separated the microprotist community into five groups, which contain 25, 22, 6, 4 and 2 stations. The largest group was observed on the Chukchi Sea shelf, showing a high abundance predominated by diatoms (78 % of total abundance). The second group was observed from the East Siberian Sea to the Canada Basin, characterised by low abundance and ciliate dominance (36 % of total abundance). Because of the high abundance and predominance of diatoms, the former group is characterised by eutrophic waters, which are enhanced by the continuous inflow of the nutrient-rich Pacific Water through the Bering Strait. Due to the low abundance and the dominance of ciliates, the latter group is dominated by organisms of the microbial food web. The remaining three groups were smaller and located between the two large groups. The distribution of these three groups may be based on complex physical structures, such as the anticyclonic eddy near the shelf break.