Latitudinal variation of phytoplankton communities and carbon biomass in the western Arctic Ocean

Abstract

A number of recent studies showed that photosynthetic eukaryotes are an active and often dominant component of Arctic algal assemblages. In order to place these observations in a large-scale context, samples were collected to investigate the community structure and biomass of phytoplankton along a transect in the western Arctic Ocean. The transect included 37 stations at surface and sub-chlorophyll-a maximum (SCM) depths in the Bering Sea, Chukchi Sea and Canadian Basin from July 19 to September 5, 2008. Phytoplankton (>2 μm) were identified and counted by light microscopy. Cluster analysis of abundances and biomass revealed different assemblages over the shelf, slope and basin regions. The spatial distribution of phytoplankton was heterogeneous along the transect. Phytoplankton communities were composed of 71 taxa representing Dinophyceae, Cryptophyceae, Bacillariophyceae, Chrysophyceae, Dictyochophyceae, Prasinophyceae and Prymneosiophyceae. The most abundant species were nano-pico sized phytoplankton at surface and SCM depths of most stations, but the second dominant species were variable by stations. Overall, the phytoplankton community was strongly dominated by 10 general, dominant species were Thalassiosira sp., Chaetoceros sp. and unidentified nano-pico phytoplankton such as Dinobryon belgica and Cryptomonas sp. Phytoplankton abundance reached a maximum of 8.29 x 106 cells mL&#8211

1 at station R09(surface). Nano and pico sized phytoplankton were tentatively dominant in the Bering Sea, whereas diatoms and nano sized plankton were major taxonomy communities in the Bering Strait and Chukchi Sea. From the western Bering Sea to the Bering Strait, the abundance and biomass of phytoplankton were getting greater and species diversity was richer, but after passing through the Bering Strait these parameters decreased providing a latitudinal gradient to the central Arctic. Although nano and pico phytoplankton were the important contributors for increasing cell abund