Abstract:

Background and Aims The phytoplankton in the Arctic seas is rarely explored on a large geographic scale, particularly at the community level.The diversity, density and distribution variability of netphytoplankton assemblages were measured at 49 stations in the Chukchi Sea (66°0.3'-75°18.6' N, 153°36.5'-174°59.5' W) and Bering Sea (55°59.8'-66°0.3' N, 173°21.1' E-175°53.9' W) during the FCNARE (1999) cruise on the Xuelong Research Vessel of SOA, China.

Methods The diversity indices combining the data on the abundance within a species in a community into a single number were adopted to understand the state of the community. Principal component analysis (PCA) of data was applied for examing the distribution variability of netphytoplankton. Cluster analysis was used as indicative of the degree of similarity in species composition among stations to the selected species having a frequency of occurrence greater than 10% of the total samples.

Key Results Both the mean index values of phytoplankton diversity and evenness were approximately equally low at the two study areas, ranging from 1.88 to 1.90 and from 0.43 to 0.45, respectively. However,both the average cell density and total species numbers in the Chukchi Sea were far greater than these in the Bering Sea, reaching 9 122.56×10⁴ cells·m^-3 and 103 taxa in the Chukchi Sea but only 161.78×10⁴ cells·m^-3 and 71 taxa in the Bering Sea. The results of PCA indicated that the first two components (the most important species variables) explained 33.0% of the total variance in the netphytoplankton distribution in the study areas. The main populations belong to the arctic-boreal community (pan-arctic community) and boreal oceanic community, including some centric diatoms in the arctic-boreal community, such as Chaetoceros curvisetus, C. debilis, C. socialis, C.furcellatus etc. belonging to the Chaetoceros-Oligochromatophorus group, and Lauderia glacialis, Leptocylindrus danicus, Thalassiosira nordenskioldii and Bacteriosira fragilis etc., as well as Corethron criophilum, Proboscia truncata, P. inermis, Dentecula seminaeandsome and some species belonging to Chaetoceros-Phaeoceros-Polychromatophorus group such as Chaetoceros atlanticus etc. in the boreal oceanic community. Seven major netphytoplankton regions containing different phytoplankton communities in two study areas were distinguished by the cluster analysis. However, the extremely dynamic physical nature of the drifting pack ice (e.g. packing, breaking up and melting) introduce short-term variability into the water conditions that no doubt affect the species composition; hence, the groupings of the netphytoplankton in the different regions may reflect temporal conditions, particularly in the Chukchi Sea, that require repeated sampling in order to better classify the regions.

Conclusions There were strong differences in the density and taxa of the netphytoplankton between the Chukchi Sea and Bering Sea. The density and composition were highly variable among sampling sites, particularly in Chukchi Sea.

Key words: Chukchi Sea and Bering Sea, Netphytoplankton, Distribution, Ecology, Multivariate analysis