Mi-Ok Park

Production of mycosporine-like amino acids of in situ phytoplankton community in Kongsfjorden, Svalbard, Arctic

The spatial distribution of UV-absorbing compounds (mycosporine-like amino acids, MAAs), was investigated by comparing the phytoplankton community structures in the inner and outer waters of the Kongsfjorden inlet, which is located in arctic Svalbard. Thalassiosira sp. and Phaeocystis sp. were dominant in the outer waters of the Kongfjorden inlet, demonstrating high chlorophyll a (chl a) concentrations and low MAA concentrations in the outer bay waters. However, Kongsfjorden Bay was dominated by Phaeocystis sp. and demonstrated high MAA concentrations despite low chl a concentrations. The carbon fixation rate at a station located inside Kongsfjorden Bay (T05) was significantly photo-inhibited by UV radiation, demonstrating higher production rates of MAA and chl a than at a station (B09) in outer bloom waters. Additionally, the turnover rates of individual MAAs were faster inside the Kongsfjorden Bay than in the outside waters. As a result, the natural phytoplankton community demonstrated different UV adaptation mechanisms according to the phytoplankton species, in this case, Thalassiosira sp. vs. Phaeocystis sp. It is possible to understand real-time changes for newly photosynthesized MAAs as UV-absorbing compounds in the natural phytoplankton community. This takes place via determination of in situ MAA production rates using (13)C tracer and High Performance Liquid Chromatography (HPLC) combined with an isotope ratio mass spectrometer (irMS).

Phytoplankton and Primary Production

The northern part of the East Sea (Japan Sea) is dominated by the cold waters of the Liman Current, whereas in the southern part, the dominant current is the Tsushima Warm Current. Together with these major current systems, subpolar fronts and mesoscale eddies that form in the region exert a strong influence on the phytoplankton ecosystem in the East Sea. These conspicuous physical forcings are manifested as often clearly discernible features in temporal and spatial distributions, composition, abundance, biomass and production of phytoplankton. In short, diatoms and dinoflagellates are found to be the most diverse phytoplankton groups and are occasionally responsible for blooms in coastal waters. Diatoms are also abundant in frontal areas and in the rings of warm core eddies. Picophytoplankton groups are also found to be important phytoplankton in the East Sea, especially in warm seasons, and photosynthetic picoeukaryotes and Synechococcus show distinct seasonal and vertical distribution patterns. Recent field measurements indicated that the spatial distribution of primary productivity in the Ulleung Basin (UB) of the East Sea ranged from 172 to 358 g C m−2 year−1. This range of primary productivity is relatively higher than in other regions in the East Sea. The East Sea is a body of dynamic “non-oceanic” water with its own particular oceanic characteristics. Coastal upwelling and mesoscale eddies over a wide range of horizontal scales contribute to the high primary productivity in the UB. This vibrant primary production provides the foundation for a biological “hot” spot and strong support for an energetic biological pump cycle in the East Sea. Despite much progress in expanding knowledge of phytoplankton ecology in the East Sea, more studies on diversity, productivity, niche, and physiological adaptation to dynamic environments should be conducted to better understand ecological roles of phytoplankton in changing oceans.