ALBERT

Description: There is a controversy discussion about the contribution of the genus Phaeocystis to the vertical carbon export with evidence for and against sedimentation of Phaeocystis. So far, the presence of Phaeocystis in sinking matter was investigated with methods depending on morphological features (microscopy) and fast degradable substances (biochemical analyses). In this study, we determine the occurrence and abundance of Phaeocystis antarctica in short-term sediment traps and the overlying water column during a 12-day time period in the Atlantic sector of the Southern Ocean with 454-pyrosequencing and microscopy counting. In the sediment trap samples, we only found few sequences belonging to Phaeocystis, which was not reflecting the situation in the water column above. The cell counts showed the same results. We conclude that Phaeocystis cells are not generally transported downwards by active sinking or other sinking processes.

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: 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.

Description: Protists in the central Arctic Ocean are adapted to the harsh environmental conditions of its various habitats. During the Polarstern cruise ARK-XXVI/3 in 2011, at one sea ice station, large aggregates accumulated at the bottom of the melt ponds. In this study, the protist assemblages of the bottom layer of the sea ice and melt pond aggregate were investigated using flow cytometry and 454-pyrosequencing. The objective is to provide a first molecular overview of protist diversity in these habitats and to consider the overlaps and/or differences in the community compositions. Results of flow cytometry pointed to a cell size distribution that was dominated by 3-10 µm nanoflagellates. The phylogenetic classification of all sequences was conducted at a high taxonomic level, while a selection of abundant (≥1% of total reads) sequences was further classified at a lower level. On the high taxonomic level, both habitats showed very similar community structures, dominated by chrysophytes and chlorophytes. On the lower taxonomic level, dissimilarities in the diversity of both groups were encountered in the abundant biosphere. While sea ice chlorophytes and chrysophytes were dominated by Chlamydomonas/Chloromonas spp and Ochromonas spp, the melt pond aggregate was dominated by Carteria sp., Ochromonas spp. and Dinobryon faculiferum. We suppose that the relatively high similarity in diversity is a consequence of melt pond freshwater seeping through porous sea ice in late summer. Differences in the abundant biosphere nevertheless indicate that differences in both habitats are also strong enough to select for different dominant species.

Description: Investigation of marine eukaryotic picoplankton composition is limited by missing morphological features for appropriate identification. Consequently, molecular methods are required. In this study, we used 454-pyrosequencing to study picoplankton communities at four stations in the West Spitsbergen Current (WSC; Fram Strait). High abundances of Micromonas pusilla were detected in the station situated closest to Spitsbergen, as seen in surveys of picoplankton assemblages in the Beaufort Sea. At the other three stations, other phylotypes, affiliating with Phaeocystis pouchetii and Syndiniales in the phylogenetic tree, were present in high numbers, dominating most of them. The picoplankton community structures at three of the stations, all with similar salinity and temperature, were alike. At the fourth station, the influence of the East Spitsbergen Current (ESC), transporting cold water from the Barents Sea around Spitsbergen, causes different abiotic parameters that result in a significantly different picoeukaryote community composition, which is dominated by Micromonas pusilla. This observation is particularly interesting in regard to ongoing environmental changes in the Arctic. Ongoing warming of the WSC could convey a new picoplankton assemblage into the Arctic Ocean, which may come to affect the dominance of Micromonas pusilla.

Description: Monitoring changes in eukaryotic microbial communities is critical for understanding ecosystem dynamics, trophic interactions and the impacts of climate change. Long-term time series are an important tool for monitoring changes in ecological communities, but time series from a single location may not be representative of regional dynamics. In the German Bight, the Helgoland Roads time series is such a long-term series. Here, we consider the spatial dynamics of the eukaryotic microbes as an indicator of the representativeness of the Helgoland Roads site for the coastal German Bight, which is located in the North Sea. The eukaryotic microbial community in the German Bight was analysed at Helgoland Roads and two coastal stations (Cuxhaven and Wilhelmshaven) between March and October 2016 using metabarcoding. In addition, an oceanographical model was used to check for potential hydrological connectivity between the stations during the sampling period. Our results showed that the communities were different at the three stations. Helgoland was dominated by dinoflagellates, whereas the coastal stations had more diverse communities. Furthermore, differences were observed in the dinoflagellate and diatom communities between the three stations. Lagrangian particle tracking applied to the model results, showed limited connectivity between Helgoland and the coastal stations in 2016. The differences between Helgoland and the coastal stations were correlated with the different hydrological regimes and associated nutrient contents. Our observations suggest the presence of different eukaryotic microbial communities separated by complex hydrological conditions in the coastal German Bight.

Description: It is important to characterize and understand the diversity of marine protists because of their relevance for ecosystem functioning. In the era of molecular science, diversity studies have received renewed attention. High-throughput, cost-intensive next generation sequencing provides deep insight in protist diversity but limits the volume of studied samples. Protist observations with high spatiotemporal resolution, therefore, require a quick and cost-effective tool to channelize the large sample volume and help select representatives for diversity studies. In this study, we evaluated the validity of “Automated Ribosomal Intergenic Spacer Analysis” (ARISA) as a means of estimating variability in marine protist communities. The evaluation was based on statistical correlation of ARISA data and 454-pyrosequencing data from samples collected in the Southern Ocean and Arctic Ocean. Here, we provide evidence that differences in ARISA profiles reflect taxon-specific differences observed in 454-pyrosequencing data sets. Calculated similarity indices for the ARISA profiles and 454- pyrosequencing data of 27 marine protist samples revealed strong agreements between the results of both methods regarding the extent of variability among protist communities. We suggest that ARISA might become an important tool for surveillance of differences in marine protist communities with high spatiotemporal resolution. Furthermore, it might serve as a preselection tool to identify representative samples in large data sets.

Description: Time-series studies of arctic marine ecosystems are rare. This is not surprising since polar regions are largely only accessible by means of expensive modern infrastructure and instrumentation. In 1999, the Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) established the LTER (Long-Term Ecological Research) observatory HAUSGARTEN crossing the Fram Strait at about 79°N. Multidisciplinary investigations covering all parts of the open-ocean ecosystem are carried out at a total of 21 permanent sampling sites in water depths ranging between 250 and 5,500 m. From the outset, repeated sampling in the water column and at the deep seafloor during regular expeditions in summer months was complemented by continuous year-round sampling and sensing using autonomous instruments in anchored devices (i.e., moorings and free-falling systems). The central HAUSGARTEN station at 2,500 m water depth in the eastern Fram Strait serves as an experimental area for unique biological in situ experiments at the seafloor, simulating various scenarios in changing environmental settings. Long-term ecological research at the HAUSGARTEN observatory revealed a number of interesting temporal trends in numerous biological variables from the pelagic system to the deep seafloor. Contrary to common intuition, the entire ecosystem responded exceptionally fast to environmental changes in the upper water column. Major variations were associated with a warm water anomaly evident in surface waters in eastern parts of the Fram Strait between 2005 and 2008. However, even after 15 years of intense time-series work at HAUSGARTEN, we cannot yet predict with complete certainty whether these trends indicate lasting alterations due to anthropologically-induced global environmental changes of the system, or whether they reflect natural variability on multiyear time-scales, for example, in relation to decadal oscillatory atmospheric processes.

Description: Investigation of phytoplankton biodiversity, ecology, and biogeography is crucial for understanding marine ecosystems. Research is often carried out on the basis of microscopic observations, but due to the limitations of this approach regarding detection and identification of picophytoplankton (0.2–2 μm) and nanophytoplankton (2–20 μm), these investigations are mainly focused on the microphytoplankton (20–200 μm). In the last decades, various methods based on optical and molecular biological approaches have evolved which enable a more rapid and convenient analysis of phytoplankton samples and a more detailed assessment of small phytoplankton. In this study, a selection of these methods (in situ fluorescence, flow cytometry, genetic fingerprinting, and DNA microarray) was placed in complement to light microscopy and HPLC-based pigment analysis to investigate both biomass distribution and community structure of phytoplankton. As far as possible, the size classes were analyzed separately. Investigations were carried out on six cruises in the German Bight in 2010 and 2011 to analyze both spatial and seasonal variability. Microphytoplankton was identified as the major contributor to biomass in all seasons, followed by the nanophytoplankton. Generally, biomass distribution was patchy, but the overall contribution of small phytoplankton was higher in offshore areas and also in areas exhibiting higher turbidity. Regarding temporal development of the community, differences between the small phytoplankton community and the microphytoplankton were found. The latter exhibited a seasonal pattern regarding number of taxa present, alpha- and beta-diversity, and community structure, while for the nano- and especially the picophytoplankton, a general shift in the community between both years was observable without seasonality. Although the reason for this shift remains unclear, the results imply a different response of large and small phytoplankton to environmental influences.

Description: In the ongoing discussion of the distribution of protists, whether they are globally distributed or endemic to one or both of the polar regions is the subject of heated debate. In this study, we compared next-generation sequencing data from the Arctic and the Southern oceans to reveal the extent of similarities and dissimilarities between the protist communities in the polar regions. We found a total overlap of operational taxonomic units (OTUs) between the two regions of 11.2%. On closer inspection of different taxonomic groups, the overlap ranged between 5.5% (haptophytes) and 14.5% (alveolates). Within the different groups, the proportion of OTUs occurring in both regions greatly differed between the polar regions. On the one hand, the overlap between these two regions is remarkable, given the geographical distance between them. On the other hand, one could expect a greater overlap of OTUs between these regions on account of the similar environmental conditions. The overlap suggests a connection between the polar regions for at least certain species or that the evolutionary divergence has been slow, relative to the timescales of isolation. The different proportions of common OTUs among the groups or regions may be a result of different life cycle strategies or environmental adaptations.