Asthe most abundant and the most taxonomically and genetically diverse organisms in the marine ceosystem, nanoplankton predominate in the marine system concerning their bioactivity, biomass, and production. They play an important role in the carbon fixation process in the Arctic Ocean, and are an important component to regulate the biosphere. Furtherly, nanoplankton can be an important indicator of the changing environment, since the changes in the community, structure and biomass of nanoplankton reflect the changes in the pathways of nutrient and energy transferring in the food web and the changes in the biogeochemical cycle. Recently, ecology study of the Arctic nanoplankton has been paid more attention due to the increasing impacts of climate change on the Arctic marine ecosystems. Substantial progress has been achieved.
The Arctic heterotrophic bacteria were reported to resemble those in the seas of lower altitudes in their high abundance and biomass with seasonal successions. Particle-associated bacteria often show a higher specific metabolic activity than the free-living communities. So far, there are few reports on the proteorhodopsin (PR)-containing bacteria. High diversity has been reported for this group in the Chukchi Sea, which can be attribute to yariable bacteria communities. A large number of aerobic anoxygenic phototrophic (AAP) bacteria have been found in the Chukchi Sea with a distinctly seasonal succession. The photosynthetic group in the Arctic Ocean was found to be mostly composed with the nanoplankton (≤20μm), described as a polar ecotype of the small prasinophyte Micromonas. The high correlation between the abundance of coccoid cynaobacteria and temperature results their low abundance at the high latitudes There are only a few studies of Synechococcus in the coastal Arctic Ocean. The Micromonas is proved to be ubiquitous throughout the Arctic Ocean, especially at the chlorophyll-maximum layer, and may be a major contributor to the primary production in the Arctic Ocean. Until now little is known about the distribution of heterotrophic nanoflagellates in the Arctic Ocean, compared with phytoplankton and prokaryotes.
Many scientific questions, which deserve special attention, remain unsolved due to lack of continuous sampling and the complexity of the nanoplankton characteristics. Some of them have been highlighted here in the Arctic nanoplankton ecology. (1) More attention should be paid to the effect of the climate change on the nanoplankton community in the Arctic Ocean, considering its major and often dominant contribution to the total ecosystem. (2)Most of the investigations of nanoplankton community are focused on the Atlantic Arctic Ocean of the Arctic Ocean. It is necessary to investigate the community structure of the nanoplankton in the entire Arctic Ocean. (3) As a photoheterotrophic microbe, AAP bacteria may play a special role in the ecology in the Arctic Ocean. However, little is known about the distribution, abundance, and diversity of the AAP bacteria in Arctic Ocean. (4)Archaea seems to be of special significance in the Arctic waters with large population existing in the surface water. More work need to be done on their diversity and their functions in the energy flow.