Description: Climate change is expected to be particularly intense in the Arctic Ocean having as well extensive consequences on Arctic pelagic ecosystems. Thus, evaluations of the impact on the base of the food web, on local phytoplankton communities, are required. Prerequisite of such an evaluation is comprehensive information about the present phytoplankton diversity and distribution. Recent investigations indicate that rising temperatures as well as freshening of surface waters in the marine environment promote a shift in the phytoplankton community towards a dominance of smaller cells. In such a scenario, picoplankton can comprise a large pool of biomass and can attain high abundances. Understanding the impact of climate related environmental change for this phytoplankton size class in the Arctic Ocean demands that we understand how environmental parameters influence their diversity, occurrence and distribution. In this perspective, samples to investigate picoplankton have been taken in the area of the “deep-sea long-term observatory HAUSGARTEN” of the Alfred-Wegener-Institute (Fram Strait) in July 2009 and analyzed by the application of ribosomal fingerprinting technology (ARISA), 18S rDNA clone libraries and Pyrosequencing. The investigation area between 2 - 6°E and 78 – 80°N is located within the frontal zone which is separating the warm and cold water masses originating from the West Spitzbergen Current and East Greenland Current, respectively. Based on the heterogeneous hydrographic condition differences in the picoplankton community according to the water masses is likely. Preliminary results on the investigation of the genetic diversity of picoplankton reflect these environmental differences. The findings reveal that the diversity within the warm water mass is higher compared to the one found in the colder water mass. Further the dominance of single species (Phaeocystis pouchetii vs. Micromonas pusilla) differs at the stations according to abiotic conditions. All in all, this study will provide a framework for a better understanding of the interactions between environmental conditions and corresponding pico-phytoplankton communities in arctic pelagic systems.

Description: Studies of phytoplankton ecology and biogeochemical parameters have been carried out with the ice breaking vessel RV Polarstern since the nineties at various locations in the central Artcic Ocean, the Greenland Sea and the Fram Strait, however, plankton abundance and composition were determined sporadically, and only few biogeochemical components were analysed. Since rapid environmental changes due to increasing temperatures, sea ice loss and ocean acidification in the Arctic Ocean are expected, a more comprehensive impression of the impact of the anticipated changes on pelagic biological processes and the consequences for organic matter cycling is desirable. To get more detailed investigations on the pelagic system the new research group PEBCAO was created. The aim of this group is to complement the measurements of bulk variables and samples on phyto- and protozooplankton abundances by a molecular assessment of the phytoplankton diversity, including the pico- and nanoplankton allowing to better quantifying the intrusion of invading species into the polar habitat. The point measurements during cruises will serve as ground-truthing data to create basin wide satellite images focussing on the quantitative estimation of various phytoplankton functional types, which can serve as an input for modelling approaches. Furthermore, investigations on changes in the composition of organic matter (OM) including molecular analysis of OM are carried out and together with abundance and activity of key species in zooplankton will improve the export estimates under climate change. One local focus of this group is the deep-sea long-term observatory HAUSGARTEN of AWI in the Fram Strait off Svalbard, where investigations on plankton ecology and particle flux have been carried out since the 1990. These observations can be used to identify how current observed changes are related in a historical context. Here we present first results of the multidisciplinary approach form the long term observations and the studies carried out during two Polarstern cruises (ARK 24_1&2 and ARK 25_1&2) in the summer of 2009 & 2010, respectively.

Description: Most of the iron fertilization experiments conducted in the Southern Ocean during the past two decades were carried out in high silicic acid waters and have induced phytoplankton blooms, dominated by diatoms. The iron fertilization experiment LOHAFEX, performed during the RV Polarstern cruise ANT XXV/3 from January to March 2009, was however carried out in a silicic acid depleted mesoscale eddy in the Atlantic sector of the Southern Ocean. The low silicic acid concentrations (〈2 µM) limited diatom growth and the phytoplankton assemblage was instead dominated by nano- and picoeukaryotes. In the present study we used molecular methods to investigate the composition and succession of small phytoplankton (0.2-5µm) during LOHAFEX. This involves on the one hand ARISA (automated intergenic spacer analysis) and on the other hand 454 next generation sequencing. The ARISA approach is based on the heterogeneity of the region between the 18S and the 28S rRNA gene and delivers a quick community structure overview. The 454 sequencing is a high throughput approach and provides high resolution information on the phytoplankton diversity, including the rare biosphere. During LOHAFEX the 0.2-5µm phytoplankton fraction shows a high diversity. The most prominent classes are the Prasinophyceae (dominated by Micromonas pusilla), the Haptophyceae (dominated by Phaeocystis antarctica) and the Dinophyceae (dominated by Syndiniales). The fertilized and non-fertilized samples show a similar community structure and no significant differences concerning the abundance of the dominant species. In all samples there are a large number of sequences belonging to the rare biosphere. The results support the general notion that the diversity of the picoplankton community was highly underestimated in the past. There is still a vast number of unknown organisms, hiding in the rare biosphere, to discover. According to other studies, our outcome shows that in the northern part of the Southern Ocean the picoplankton assemblage is dominated by Micromonas pusilla and Phaeocystis antarctica. Measurements during the experiment revealed an increase in total biomass, attributed to the addition of iron. In our samples there is no species or group in the picoplankton community that is favored by the iron addition and the relative abundances remain constant. In conclusion the iron addition has increased picoplankton biomass but the assemblage composition did not change significantly.

Description: Between Greenland and Spitsbergen, Fram Strait is a region where cold ice-covered Polar Water exits the Arctic Ocean with the East Greenland Current (EGC) and warm Atlantic Water enters the Arctic Ocean with the West Spitsbergen Current (WSC). In this compilation, we present two different data sets from plankton ecological observations in Fram Strait: (1) long-term measurements of satellite-derived (1998–2012) and in situ chlorophyll a (chl a) measurements (mainly summer cruises, 1991–2012) plus protist compositions (a station in WSC, eight summer cruises, 1998–2011); and (2) short-term measurements of a multidisciplinary approach that includes traditional plankton investigations, remote sensing, zooplankton, microbiological and molecular studies, and biogeochemical analyses carried out during two expeditions in June/July in the years 2010 and 2011. Both summer satellite-derived and in situ chl a concentrations showed slight trends towards higher values in the WSC since 1998 and 1991, respectively. In contrast, no trends were visible in the EGC. The protist composition in the WSC showed differences for the summer months: a dominance of diatoms was replaced by a dominance of Phaeocystis pouchetii and other small pico- and nanoplankton species. The observed differences in eastern Fram Strait were partially due to a warm anomaly in the WSC. Although changes associated with warmer water temperatures were observed, further long-term investigations are needed to distinguish between natural variability and climate change in Fram Strait. Results of two summer studies in 2010 and 2011 revealed the variability in plankton ecology in Fram Strait.

Description: The protist assemblage in the central Arctic Ocean is scarcely surveyed despite them being the major primary producers. Elucidating their response to changing environmental variables requires an a priori analysis of their current diversity, including abundant and rare species. In late summer 2011, samples were collected during the ARK-XXVI/3 expedition (RV Polarstern) to study Arctic protist community structures, by implementation of automated ribosomal intergenic spacer analysis (ARISA) and 454-pyrosequencing. Protist assemblages were related to the hydrology and environmental variables (temperature, salinity, ice coverage, nitrate, phosphate, and silicate). The abundant (a parts per thousand yen1 %) biosphere and rare (〈 1 %) biosphere were considered separately in the diversity analysis in order to reveal their mutual relationships. A relation between hydrology and protist community structure was highly supported by ARISA and partially by 454-pyrosequencing. Sea ice showed a stronger influence on the local community structure than nutrient availability, making statements on the water mass influence more difficult. Dinoflagellates (Syndiniales), chlorophytes (Micromonas spp.), and haptophytes (Phaeocystis spp.) were important contributors to the abundant biosphere, while other dinoflagellates and stramenopiles dominated the rare biosphere. No significant correlation was found between the abundant and rare biosphere. However, relative contributions of major taxonomic groups revealed an unexpected stable community structure within the rare biosphere, indicating a potential constant protist reservoir. This study provides a first molecular survey of protist diversity in the central Arctic Ocean, focusing on the diversity and distribution of abundant and rare protists according to the environmental conditions, and can serve as baseline for future analysis.

Description: Sequencing of 18S rDNA clone libraries and 454-pyrosequencing are valuable methods used to describe microbial diversity. The massively parallel 454-pyrosequencing generates vast amounts of ribosomal sequence data and has the potential to uncover more organisms, even rare species. However, the relatively short sequence lengths of ~500 bp are suboptimal for taxonomic annotation and phylogenetic analyses. In this study, we assessed the potential of 18S ribosomal clone libraries to complement corresponding 454-pyrosequencing data with near full-length sequence information. This involved a comparison of protist community compositions in five polar samples suggested by 18S rDNA clone libraries with the corresponding community compositions suggested by 454-pyrosequencing. The study was conducted with four Arctic water samples, focusing on the eukaryotic picoplankton (0.4-3 µm), and with one sample collected in the Southern Ocean, examining the whole size spectrum (〉0.4 µm). For all individual samples, the protist community compositions suggested by the two different approaches showed significant similarities. Around 70% of the sequences detected by sequencing of clone libraries were also present in the 454-pyrosequencing data set. However, the clone library sequences reflected only ~20% of the abundant biosphere identified by 454-pyrosequencing and identified ribosomal sequences, that were not detected in the 454-pyrosequencing data sets.

Description: In this study we present the first comprehensive analyses of the diversity and distribution of marine protist (micro- nano- and picoeukaryotes) in the Western Fram Strait, using 454-pyrosequencing and high-pressure liquid chromatography (HPLC) at five stations in summer 2010. Three stations (T1; T5; T7) were influenced by Polar Water, characterized by cold water with lower salinity (〈33) and different extents of ice-concentrations. Atlantic Water influenced the other two stations (T6; T9). While T6 was located in the mixed water zone characterized by cold water with intermediate salinity (~33) and high ice-concentrations, T9 was located in warm water with high salinity (~35) and no ice-coverage at all. General trends in community structure according to prevailing environmental settings, observed with both methods, coincided well. At two stations, T1 and T7, characterized by lower ice concentrations, diatoms (Fragilariopsis sp., Porosira sp., Thalassiosira spp.) dominated the protist community. The third station (T5) was ice-covered, but has been ice-free for ~4 weeks prior to sampling. At this station, dinoflagellates (Dinophyceae 1, Woloszynskia sp. and Gyrodinium sp.) were dominant, reflecting a post-bloom situation. At station T6 and T9, the protist communities consisted mainly of picoeukaryotes, e.g. Micromonas spp. Based on our results, 454-pyrosequencing has proven to be an adequate tool to provide comprehensive information on the composition of protist communities. Furthermore, this study suggests that a snap-shot of a few, but well-chosen samples can already provide an overview of community structure patterns and successions in a dynamic marine environment.