Insight into protist diversity in Arctic sea ice and melt-pond aggregate obtained by pyrosequencing

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 biodiversity 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. At a high taxonomic level, both habitats showed very similar community structures, dominated by chrysophytes and chlorophytes. At a 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 similarities in richness and community structure are a consequence of melt-pond freshwater seeping through porous sea ice in late summer. Differences in the abundant biosphere nevertheless indicate that environmental conditions in both habitats vary enough to select for different dominant species

Summertime plankton ecology in Fram Strait - a compilation of long- and short-term observations

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

High-resolution monitoring of marine protists based on an observation strategy integrating automated on-board ship filtration and molecular analyses

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

Picoplankton: The successful spreading over the Arctic Ocean

The Arctic Ocean is a threatened environment and climate change is expected to be particularly intense by having extensive consequences on the pelagic ecosystem. Hence, 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 towards picoeukaryotes. In such a scenario, picoplankton can comprise a large pool of biomass by attaining 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 variables influence their diversity, occurrence and distribution. In this perspective sampling has take place in the central Arctic Ocean, the Laptev Sea and the Fram Strait to obtain divers hydrodynamic conditions. Thereby, special focus is set on sampling the latter area since it implies a frontal zone separating water masses originating from the WSC (West Spitsbergen Current) and EGC (East Greenland Current) and constitutes the main water exchange into the Arctic Ocean. Consequently anticipated intrusions of invasive species into the polar habitat are likely to be first reported in this region why it is regularly sampled on annual basis (2009, 2010 and 2011). The analysis has been carried out by the application of ribosomal fingerprinting technology (ARISA) to assess the community structure and of Next Generation Sequencing to analyze the diversity assessment. Preliminary results on the investigation of the genetic diversity reflect the environmental differences by presenting different community structures according to the water masses. Further the findings reveal a comparatively higher diversity within the warm water masses. By keeping the track of the Atlantic Water the dominance of single species like Phaeocystis pouchetii attracts attention wherein the influences of the Kongsfjord fortunate more tolerable species like Micromonas pusilla. The community structure of the EGC by contrast displays a distinct community structure and point to a different diversity within the current. So far picoplankton can have a high share of total protist biomass in aquatic systems, so that changes in their diversity or abundance are likely to affect prospectively pelagic food web systems up to higher trophic levels. Our results indicate the necessity of considering ocean hydrodynamics in the course of investigations and assessments of the distribution and diversity of picoeukaryotes. Altogether, this study shall deliver a framework for better understanding the interactions between environmental conditions and corresponding picophytoplankton communities by assessing the presence of biogeographic patterns

Protists in the polar regions: comparing occurrence in the Arctic and Southern oceans using pyrosequencing

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

Genetic Diversity of Eukaryotic Picoplankton in the Arctic Ocean (Fram Strait)

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

Characterizing variability in marine protist communities via ARISA fingerprints — a method evaluation

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