Antarctic Science 25(6), 741–751 (2013) & Antarctic Science Ltd 2013 doi:10.1017/S0954102013000229 Regional variability in eukaryotic protist communities in the Amundsen Sea CHRISTIAN WOLF 1 , STEPHAN FRICKENHAUS 1 , ESTELLE S. KILIAS 1 , ILKA PEEKEN 1,2 and KATJA METFIES 1 1 Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany 2 MARUM - Centre for Marine Environmental Sciences, University of Bremen, Leobener Straße, 28359 Bremen, Germany Christian.Wolf@awi.de Abstract: 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. Received 3 September 2012, accepted 15 February 2013, first published online 16 April 2013 Key words: ARISA, HPLC, microbial diversity, next-generation-sequencing, phytoplankton Introduction The Pacific sector of the Southern Ocean, and especially the Amundsen Sea, are the least studied oceanic regions in the world (Griffiths 2010). Severe ice conditions year-round and the geographic remoteness make sampling in this area very difficult. The biodiversity of the Amundsen Sea, especially of the coastal and shelf areas, is almost unknown (Kaiser et al. 2009). Recently, scientists began to highlight the diversity and distribution of isopods and phytoplankton in this isolated region (Kaiser et al. 2009, Fragoso & Smith 2012). Gravalosa et al. (2008) concentrated on the distribution of coccolithophores and showed that their dispersion is restricted north of the Polar Front. Fragoso & Smith (2012) focused their study areas near the coast and delivered an overview of the phytoplankton assemblages in this area. They revealed diatom dominated assemblages in offshore areas of the Amundsen Sea. However, they used pigment based and microscopic analysis and thereby, the taxonomical resolution was not very detailed. So far, no comprehensive survey of the whole eukaryotic protist spectrum in the Amundsen Sea exists. In the course of the controversially conducted debate about the ‘‘everything is everywhere’’ hypothesis (Lachance 2004), many studies focused on the biogeography of protists (Finlay 2002, Finlay & Fenchel 2004). Our recent study, focusing on the distribution of eukaryotic protists along a transect from New Zealand to the coast of Antarctica, revealed distinct biogeographical patterns, defined by the oceanic fronts (Wolf et al. unpublished). These patterns were driven by strong environmental gradients and included different large-scale water masses. To complement our knowledge about the biogeography of protists in the Pacific sector of the Southern Ocean, their distribution has to be highlighted on a smaller, more regional scale. Narrow environmental differences within a large-scale water mass have to be investigated. Most investigations of eukaryotic protist composition and distribution in the Southern Ocean mainly used traditional microscopic and pigment extraction based methods (Ishikawa et al. 2002, Wright et al. 2009). However, microscopic surveys have difficulties in identifying small cells and pigment analysis only targets autotrophic cells. Here, molecular tools are advantageous. Few investigations in the Southern Ocean used molecular approaches, such as denaturing gradient gel electrophoresis (DGGE) (Gast et al. 2004) or 18S rRNA gene cloning and sequencing (Lopez-Garcia et al . 2001). The automated ribosomal intergenic spacer analysis (ARISA) approach provides a quick overview of the diversity and facilitates the comparison of different samples. It is well established for investigations of prokaryotic diversity (Smith et al . 2010), and we successfully implemented it for the analysis of eukaryotic phytoplankton diversity. The newly emerging 454-pyrosequencing approach (e.g. of the V4 region of the 18S rRNA gene) allows assessing microbial communities with high-resolution, based on sufficient deep taxon sampling (Margulies et al . 2005, Stoeck et al . 2010), regardless of cell size and nutrition. The objective of this study is to determine the composition of late summer eukaryotic protist assemblages in the Amundsen Sea, south of the southern boundary of the Antarctic 741 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0954102013000229 Downloaded from https://www.cambridge.org/core. IP address: 207.241.231.48, on 02 Dec 2017 at 11:54:42, subject to the Cambridge Core terms of use, available at