J. Phycol. 49, 996–1010 (2013) © 2013 Phycological Society of America DOI: 10.1111/jpy.12109 PROTIST DISTRIBUTION IN THE WESTERN FRAM STRAIT IN SUMMER 2010 BASED ON 454-PYROSEQUENCING OF 18S RDNA1 Estelle Kilias,2 Christian Wolf, Eva-Maria Nöthig Alfred Wegener Institute for Polar and Marine Research, Bioscience, Bremerhaven 27570, Germany Ilka Peeken Alfred Wegener Institute for Polar and Marine Research, Bioscience, Bremerhaven 27570, Germany MARUM – Center for Marine Environmental Science, Bremen 28359, Germany and Katja Metfies Alfred Wegener Institute for Polar and Marine Research, Bioscience, Bremerhaven 27570, Germany In this study, we present the first comprehensive List of abbreviations: Bp, base-pair; CTD, conductiv- analyses of the diversity and distribution of marine ity temperature depth; dNTP, deoxyribonucleoside protist (micro-, nano-, and picoeukaryotes) in the triphosphate; HPLC, High-Performance Liquid Western Fram Strait, using 454-pyrosequencing and Chromatography; MODIS, Moderate Resolution high-pressure liquid chromatography (HPLC) at five Imaging Spectroradiometer; OTU, operational taxo- stations in summer 2010. Three stations (T1; T5; nomic unit; POC, particulate organic carbon T7) were influenced by Polar Water, characterized by cold water with lower salinity (<33) and different extents of ice concentrations. Atlantic Water Global warming is transforming ecosystems on an influenced the other two stations (T6; T9). While T6 extraordinary scale. Changes in the Arctic are more was located in the mixed water zone characterized intense than in other regions of the world oceans by cold water with intermediate salinity (~33) and (IPCC, Intergovernmental Panel on Climate high ice concentrations, T9 was located in warm Change. Working Group I 2007). The ongoing envi- water with high salinity (~35) and no ice-coverage at ronmental change requires evaluation of its impact all. General trends in community structure on pelagic ecosystems. These impacts could include according to prevailing environmental settings, species invasions into new areas with more tolerable observed with both methods, coincided well. At two abiotic conditions, intermingling of formerly non- stations, T1 and T7, characterized by lower ice overlapping species or the loss of genetic diversity, concentrations, diatoms (Fragilariopsis sp., Porosira particularly within local endemics (Cotterill et al. sp., Thalassiosira spp.) dominated the protist 2008). All these events have in common that they community. The third station (T5) was ice-covered, cause changes of biodiversity and thus affect the but has been ice-free for ~4 weeks prior to marine ecosystems, as well as biogeochemical sampling. At this station, dinoflagellates cycling in the Arctic (Wassmann et al. 2011). (Dinophyceae 1, Woloszynskia sp. and Gyrodinium Marine phytoplankton is the base of the pelagic sp.) were dominant, reflecting a post-bloom food web and a major contributor to the global situation. At station T6 and T9, the protist carbon cycle. The taxonomic composition as well communities consisted mainly of picoeukaryotes, as the biomass of phytoplankton influences the e.g., Micromonas spp. Based on our results, 454- Arctic marine food web, including the trophic pyrosequencing has proven to be an adequate tool interactions and the fluxes of essential nutrients to provide comprehensive information on the into the euphotic zone (Falkowski et al. 1998, Wass- composition of protist communities. Furthermore, mann et al. 2011). Protists occur in a broad size this study suggests that a snap-shot of a few, but spectrum ranging from single cells with a size well-chosen samples can provide an overview of ~0.8 lm (Courties et al. 1994) to long chains of community structure patterns and succession in a cells with sizes >200 lm. The size distribution has a dynamic marine environment. big influence on the pelagic food web structure and has the potential to affect the rate of POC Key index words: 454-pyrosequencing; ARISA; Bioge- export to deep water (Legendre and Le Fevre ography; Genetic diversity; HPLC; Phytoplankton 1991, Moran et al. 2012). In order to evaluate con- sequences of environmental change at the base of 1Received 4 November 2012. Accepted 20 July 2013. the Arctic food web, it is necessary to gain informa- 2Author for correspondence: e-mail: [email protected] tion on the temporal dynamics of phytoplankton Editorial Responsibility: T. Mock (Associate Editor) compositions and their variability in relation to 996 PROTIST DIVERSITY IN THE WESTERN FRAM STRAIT 997 changing environmental conditions (Wassmann provide comprehensive information on the protist et al. 2011). diversity, including the micro-, nano-, and pico- Until now, studies have focused on either the plankton. The data complement information on microplankton fraction (Booth and Horner 1997, the distribution of main autotrophic phyla, derived â Tremblay et al. 2006, Hegseth and Sundfjord 2008), from HPLC data, obtained by the CHEMTAX pro- or on the small size fraction, e.g., nano- and pico- gram (Mackey et al. 1996, Higgins et al. 2011). plankton (Diez et al. 2001, Lopez-Garcia et al. 2001, The Fram Strait presents an excellent observation Moon-van der Staay et al. 2001, Lovejoy et al. 2006, area to analyze the variability of marine protist com- 2007). To our knowledge, studies that cover the munities in the presence of different abiotic factors, entire size classes are scarce in the Arctic. However, because of the variable hydrographical and sea ice information on whole protist community structures conditions. The hydrography is characterized by the is essential to evaluate because all size classes con- inflow of warm and saline Atlantic Water (AW) via tribute to the functioning of marine ecosystem. Vari- the West-Spitzbergen Current (WSC) and by the ations in the phytoplankton size structure showed a outflow of cold and low saline Polar Water (PW) via trend toward smaller cell sizes, which is coupled the East Greenland Current (EGC). A significant with rising temperatures (temperature size rule) amount of the AW recirculates directly in the Fram and decreasing surface nutrient concentrations Strait, partly mixing with the colder water and (stratification-based; Atkinson et al. 2003, Bopp returning southwards (Rudels et al. 2005). et al. 2005, Daufresne et al. 2009, Moran et al. Considering the sensitivity of the Arctic Ocean to 2010, Peter and Sommer 2012). Time series studies global warming and the expected temporal and pos- of satellite derived chlorophyll a concentrations sible general shift in protist cell size, this study aims (1997–2009) observed a temporal shift in phyto- to provide information on the genetic diversity and plankton succession to earlier diatom blooms (Kah- the distribution of eukaryotic protists in the Fram ru et al. 2011), implying a shift in the succession of Strait. By achieving this, the present work also size fractions as well. A seasonal shift in protist com- relates the corresponding protist composition to the munity, from a diatom to a flagellate-based system, prevailing environmental conditions for a better was further observed during receding ice concentra- understanding of respective impacts on community tions (Moran et al. 2012). Changes in the cell size structures. dimensions and timing suggest a high relevance to include all size fractions in phytoplankton studies. In the past, a considerable number of marine MATERIALS AND METHODS surveys took advantage on ribosomal sequence Sampling area. The sampling was performed during the information, which contributed to broaden our ARK-XXV/2 expedition aboard the RV Polarstern in July understanding of phytoplankton diversity and 2010 on a transect navigated from 11°58.362′ to 11°5.09′ E community structure, including all size fractions longitude at ~78°50′ N latitude (Fig. 1). Water samples were (Medlin et al. 2006, Not et al. 2008). Automated taken in the euphotic zone by collecting seawater with 12 L ribosomal intergenic spacer analysis (ARISA) is a Niskin bottles deployed on a rosette, equipped with CTD (conductivity, temperature and depth) sensors (Table S1 in molecular, cost-effective fingerprinting method, the Supporting Information). Temperature and salinity were targeting the ribosomal operon and suitable for used from the sensor measurements, while the sea ice condi- quick comparative analyses of microbial communi- tion was determined by visual observation. In total, 16 sam- ties (Danovaro et al. 2006). ARISA is based on ples were taken in the upper 50 m water depth at the analyzing the size of intergenic spacer regions of chlorophyll maximum (exception: T1). All samples were used the ribosomal operon. So far, ARISA has been for the ARISA and a selection of five samples for further molecular and pigment analysis. For subsequent filtration, mainly used for prokaryote diversity studies (Smith 2 L water subsamples were transferred into polycarbonate et al. 2010) but recently, the method has also been bottles. In order to obtain a best possible representation of proven to be a valuable tool to assess differences in all cell sizes in the molecular approach, protist cells were the structure of marine protist communities (Wolf collected immediately by fractionated filtration (200 mbar et al. 2013). However, it is not suited to provide low pressure), through Isopore Membrane Filters (Millipore, l information on the protist community composition. Billerica, MA, USA) with pore sizes of 10, 3, and 0.4 m. Finally, the filters were transferred into Eppendorf