Diversity and Distribution of Marine Microbial Eukaryotes in the Arctic Ocean and Adjacent Seas

Abstract

We analyzed microbial eukaryote diversity in perennially cold arctic marine waters by using 18S rRNA gene clone libraries. Samples were collected during concurrent oceanographic missions to opposite sides of the Arctic Ocean Basin and encompassed five distinct water masses. Two deep water Arctic Ocean sites and the convergence of the Greenland, Norwegian, and Barents Seas were sampled from 28 August to 2 September 2002. An additional sample was obtained from the Beaufort Sea (Canada) in early October 2002. The ribotypes were diverse, with different communities among sites and between the upper mixed layer and just below the halocline. Eukaryotes from the remote Canada Basin contained new phylotypes belonging to the radiolarian orders Acantharea, Polycystinea, and Taxopodida. A novel group within the photosynthetic stramenopiles was also identified. One sample closest to the interior of the Canada Basin yielded only four major taxa, and all but two of the sequences recovered belonged to the polar diatom Fragilariopsis and a radiolarian. Overall, 42% of the sequences were <98% similar to any sequences in GenBank. Moreover, 15% of these were <95% similar to previously recovered sequences, which is indicative of endemic or undersampled taxa in the North Polar environment. The cold, stable Arctic Ocean is a threatened environment, and climate change could result in significant loss of global microbial biodiversity.The Arctic Ocean (AO) and surrounding seas have traditionally been thought of as being dominated by large phytoplankton of Ͼ20 m (67); however, recent studies show that these waters have active microbial food webs that are often dominated by cells of Ͻ3 m (37, 57) and that cells of Ͻ5 m are responsible for much of the carbon fixation over wide regions of the Arctic Basin (23, 31). The Arctic Ocean is an enclosed sea with a cold, moderately fresh (Ͻ30 practical salinity units) upper mixed layer of 30 to 60 m. These upper photic zone waters are separated from deeper waters by a strong halocline that is maintained by large riverine inputs and the annual formation and melting of sea ice (1). The physical isolation, perennially cold water temperatures (Ͻ0°C), and extreme annual light cycle provide a distinct marine habitat for microorganisms (15). 16S rRNA gene surveys have uncovered novel archaeal and eubacterial sequences from remote polar regions (6,7,12), confirming that these ambient conditions select for particular microorganisms, but there are no equivalent studies of microbial eukaryotes. North polar latitudes are predicted to warm rapidly as a result of global climate change and have already experienced significant impacts (2, 48). An assessment of current microbial diversity is therefore paramount for this region at this early stage in climate modification.Isolated and extreme environments have been important sources of novel phylotypes (33,47) that have contributed to the recent major reassessment of eukaryotic evolution (5). rRNA gene sequences from uncultured marine eukaryotes have also led to major...

Extreme diversity in noncalcifying haptophytes explains a major pigment paradox in open oceans

“…S1, Table S1). Standard eukaryotic rDNA analyses of these samples yielded Ϸ0.4-0.7% haptophyte sequences (10,11). In contrast, our data reveal hundreds of previously undescribed rDNA sequences from tiny haptophytes.…”

“…High performance liquid chromatography (HPLC) analyses of group-specific accessory pigments have further stressed the ecologic prevalence of phototrophic protist taxa. In particular, 19Ј-hexanoyloxyfucoxanthin was originally estimated to account for 20-50% of total chlorophyll a (Chla) biomass in tropical Atlantic and Pacific sites (9) and has since been consistently reported in open ocean photiczone waters, e.g., (10,11), suggesting a ubiquitous occurrence of haptophytes in upper layers of the water column. Surveys of genetic diversity based on environmental ribosomal DNA libraries over the last decade have unveiled an unexpected diversity of tiny eukaryotes in all oceans (12).…”

Comparative metagenomics of bathypelagic plankton and bottom sediment from the Sea of Marmara

“…The second more abundant group in Ma101 plankton was that of the Radiozoa (Rhizaria) with both representatives of the Acantharea and Polycystinea. Although Acantharea were slightly more abundant, all the sequences belonged to a single phylotype, closely related to an environmental sequence retrieved from Arctic waters (Lovejoy et al, 2006), whereas the Polycystinea showed a higher diversity (Supplementary Figure S14). A few sequences of haptophytes were detected in Ma101, which likely correspond to sinking cells, though it might be possible that some haptophytes are still active at this depth because of their mixotrophic capabilities.…”

Ubiquity and quantitative significance of detoxification catabolism of chlorophyll associated with protistan herbivory

“…The former belong to the two major genera Prochlorococcus and Synechococcus, which account for up to 50% of pelagic marine oxygenic photosynthesis (26)(27)(28). Eukaryotic picophytoplankton are believed to account for 20-50% of aquatic photosynthesis (29)(30)(31)(32). The use of the PCR to analyze environmental samples has also revealed the amazingly wide diversity and activity of eukaryotic picophytoplankton species (33,34).…”