Description: We determined the composition and structure of late summer eukaryotic protist assemblages along a west–east transect in the Amundsen Sea. We used state-of-the-art molecular approaches, such as automated ribosomal intergenic spacer analysis (ARISA) and 454-pyrosequencing, combined with pigment measurements via high performance liquid chromatography (HPLC) to study the protist assemblage. We found characteristic offshore and inshore communities. In general, total chlorophyll a and microeukaryotic contribution were higher in inshore samples. Diatoms were the dominant group across the entire area, of which Eucampia sp. and Pseudo-nitzschia sp. were dominant inshore and Chaetoceros sp. was dominant offshore. At the most eastern station, the assemblage was dominated by Phaeocystis sp. Under the ice, ciliates showed their highest and haptophytes their lowest abundance. This study delivers a taxon detailed overview of the eukaryotic protist composition in the Amundsen Sea during the summer 2010.

Description: Next‐generation sequencing is a common method for analysing microbial community diversity and composition. Configuring an appropriate sequence processing strategy within the variety of tools and methods is a nontrivial task and can considerably influence the resulting community characteristics. We analysed the V4 region of 18S rRNA gene sequences of marine samples by 454‐pyrosequencing. Along this process, we generated several data sets with QIIME, mothur, and a custom‐made pipeline based on DNAStar and the phylogenetic tree‐based PhyloAssigner. For all processing strategies, default parameter settings and punctual variations were used. Our results revealed strong differences in total number of operational taxonomic units (OTUs), indicating that sequence preprocessing and clustering had a major impact on protist diversity estimates. However, diversity estimates of the abundant biosphere (abundance of ≥1%) were reproducible for all conducted processing pipeline versions. A qualitative comparison of diatom genera emphasized strong differences between the pipelines in which phylogenetic placement of sequences came closest to light microscopy‐based diatom identification. We conclude that diversity studies using different sequence processing strategies are comparable if the focus is on higher taxonomic levels, and if abundance thresholds are used to filter out OTUs of the rare biosphere.

Description: Global warming is rapidly altering physicochemical attributes of Arctic waters. These changes are predicted to alter microbial networks, potentially perturbing wider community functions including parasite infections and saprotrophic recycling of biogeochemical compounds. Specifically, the interaction between autotrophic phytoplankton and heterotrophic fungi e.g. chytrids (fungi with swimming tails) requires further analysis. Here, we investigate the diversity and distribution patterns of fungi in relation to abiotic variables during one record sea ice minimum in 2012 and explore co-occurrence of chytrids with diatoms, key primary producers in these changing environments. We show that chytrid fungi are primarily encountered at sites influenced by sea ice melt. Furthermore, chytrid representation positively correlates with sea ice-associated diatoms such as Fragilariopsis or Nitzschia. Our findings identify a potential future scenario where chytrid representation within these communities increases as a consequence of ice retreat, further altering community structure through perturbation of parasitic or saprotrophic interaction networks

Description: Information on recent biomass distribution and biogeography of photosynthetic marine protists with adequate temporal and spatial resolution is urgently needed to better understand consequences of environmental change for marine ecosystems. Here we introduce and review a molecular-based observation strategy for high resolution assessment of these protists in space and time. It is the result of extensive technology developments, adaptations and evaluations which are documented in a number of different publications and the results of recently accomplished field testing, which are introduced in this review. The observation strategy is organized at four different levels. At level 1, samples are collected at high spatio-temporal resolution using the remote-controlled automated filtration system AUTOFIM. Resulting samples can either be preserved for later laboratory analyses, or directly subjected to molecular surveillance of key species aboard the ship via an automated biosensor system or quantitative polymerase chain reaction (level 2). Preserved samples are analyzed at the next observational levels in the laboratory (level 3 and 4). This involves at level 3 molecular fingerprinting methods for a quick and reliable overview of differences in protist community composition. Finally, selected samples can be used to generate a detailed analysis of taxonomic protist composition via the latest Next Generation Sequencing Technology (NGS) at level 4. An overall integrated dataset of the results based on the different analyses provides comprehensive information on the diversity and biogeography of protists, including all related size classes. At the same time the cost effort of the observation is optimized in respect to analysis effort and time.

Description: Information on recent photosynthetic biomass distribution and biogeography of Arctic marine pico-eukaryotes (0.2–3 µm) is needed to better understand consequences of environmental change for Arctic marine ecosystems. We analysed pico-eukaryote biomass and community composition in Fram Strait and large parts of the Central Arctic Ocean (Nansen Basin, Amundsen Basin) using chlorophyll a (Chl a) measurements, automated ribosomal intergenic spacer analysis (ARISA) and 454-pyrosequencing. Samples were collected during summer 2012, the year with the most recent record sea ice minimum. Chl a concentrations were highest in eastern Fram Strait and pico-plankton accounted for 60–90% of Chl a biomass during the observation period. ARISA-patterns and 454-pyrosequencing revealed that pico-eukaryote distribution is closely related to water mass distribution in the euphotic zone of the Arctic Ocean. Phaeocystaceae, Micromonas sp., Dinophyceae and Syndiniales constitute a high proportion of sequence reads, while sequence abundance of autotrophic Phaeocystaceae and mixotrophic Micromonas sp. was inversely correlated. Highest sequence abundances of Phaeocystaceae were observed in the warm Atlantic Waters in Fram Strait, while Micromonas sp. dominated the abundant biosphere in the arctic halocline. Our results are of particular interest considering existing hypotheses that environmental conditions in Nansen Basin might become more similar to the current conditions in Fram Strait. We propose that in response, biodiversity and biomass of pico-eukaryotes in Nansen Basin could resemble those currently observed in Fram Strait in the future. This would significantly alter biogeochemical cycles in a large part of the Central Arctic Ocean.

Description: nformation on recent diversity and biogeography of Arctic marine protists with adequate temporal and spatial resolution is urgently needed to better understand consequences of environmental change for marine ecosystems. Here, we introduce a molecular-based observation strategy for high resolution assessment of marine protists in space and time, even in remote areas such as the Arctic Ocean. The observation strategy involves molecular analyses (e.g. Next Generation Sequencing (NGS) or quantitative PCR) of samples, collected with a set of complementary methods such as a newly developed automated under-way sampling device, CTD-casts and moored sediment traps. This integrated approach allows generating detailed information on marine protist community composition or abundance with adequate resolution. Currently, the observation strategy is organized at four major levels. At level 1, samples are collected at high spatial and temporal resolution based on under-way sampling with the remote-controlled automated filtration system AUTOFIM (developed in the COSYNA-project), and sampling at fixed stations based on CTD-casts and moored sediment traps. Resulting samples can either be preserved for later laboratory analyses, or directly subjected to molecular surveillance of key species aboard the ship, e.g. via quantitative polymerase chain reaction (level 2). Preserved samples are analyzed at the next observational levels in the laboratory (level 3 and 4). This involves at level 3 molecular fingerprinting methods for a quick and reliable overview of differences in protist community composition. Finally, selected samples can be used to generate a detailed analysis of taxonomic protist composition via the latest Next Generation Sequencing Technology (NGS) at level 4. An overall integrated dataset of all results provides comprehensive information on the diversity and biogeography of protists, including all related size classes. In the future, the observation strategy for Arctic marine protists will be part of the Molecular Microbial Observatory envisioned for the Arctic observatory FRAM (Frontiers in Arctic Monitoring).

Description: Rising water temperatures and ocean acidification are the major threats for polar marine ecosystems and will affect phytoplankton communities. Phytoplankton plays a major role in primary production and biogeochemical cycles and forms the basis of marine food webs. Changes in the composition and distribution of phytoplankton will affect the whole marine ecosystem. To assess the effects of changing environmental conditions on phytoplankton communities we have to know their current diversity and distribution. There is a lack of Phytoplankton diversity studies in the Pacific sector of the Southern Ocean, especially in the Amundsen Sea. To resolve this gap this study will deliver basic data of phytoplankton diversity and distribution, which will help identifying the dominant phytoplankton phyla and provide information on the rare biosphere in that area. Environmental samples, taken on the RV Polarstern cruise ANT XXVI/3, were analyzed with molecular approaches, including ARISA (automated ribosomal intergenic spacer analysis) and 454-pyrosequencing. Furthermore pigment analysis and flow cytometry were conducted. First results indicate a clustering of the samples according to the different water masses and regions with comparable environmental conditions. The sequencing will deliver more detailed information about the structure and diversity of phytoplankton in the Pacific sector of the Southern Ocean.

Description: As climate change is expected to be extremely intense in the Arctic Ocean there is an utmost need to study food-web interactions to contribute to a better understanding of the direction and strength of biogeochemical and microbiological feedback processes. Climate change induced alterations will directly affect food-web structures and ecosystem functioning. Recent studies indicate that environmental changes like increasing temperatures as well as freshening of surface waters promote a shift in the phytoplankton community towards a dominance of smaller cells, especially of eukaryotic picoplankton. The response of oceanic ecosystems and marine carbon cycling to these changes is particularly determined by microbial loop activity. Heterotrophic bacteria, as part of the microbial loop and a crucial component of marine food webs, have a key role in controlling carbon fluxes in the oceans. Microbial activities, dynamics and diversity were studied in the area of the deep-sea long-term observatory HAUSGARTEN of the Alfred-Wegener-Institute (Fram Strait) in July 2009. The investigation area is located within a transition zone between the northern North Atlantic and the central Arctic Ocean, which separates the warm and cold water masses originating from the West Spitzbergen and the East Greenland currents. While bacterial abundance and chlorophyll a were tightly coupled, differences of the planktonic and bacterial community structures are most likely due to the heterogeneous hydrography. Warmer water masses comprise a higher genetic diversity of picoplankton, as it is also expected for bacteria. A shift towards a dominance of smaller plankton species can potentially affect the quality of organic matter and subsequently microbial cycling. Here we present data on bacterial abundance, biomass and protein production, hydrolytical enzyme activities and community structure within different size classes with respect to changing biotic and abiotic conditions in the Fram Strait.