Strong Seasonality of Marine Microbial Eukaryotes in a High-Arctic Fjord (Isfjorden, in West Spitsbergen, Norway)

Abstract

bThe Adventfjorden time series station (IsA) in Isfjorden, West Spitsbergen, Norway, was sampled frequently from December 2011 to December 2012. The community composition of microbial eukaryotes (size, 0.45 to 10 m) from a depth of 25 m was determined using 454 sequencing of the 18S V4 region amplified from both DNA and RNA. The compositional changes throughout the year were assessed in relation to in situ fjord environmental conditions. Size fractionation analyses of chlorophyll a showed that the photosynthetic biomass was dominated by small cells (<10 m) most of the year but that larger cells dominated during the spring and summer. The winter and early-spring communities were more diverse than the spring and summer/autumn communities. Dinophyceae were predominant throughout the year. The Arctic Micromonas ecotype was abundant mostly in the early-bloom and fall periods, whereas heterotrophs, such as marine stramenopiles (MASTs), Picozoa, and the parasitoid marine alveolates (MALVs), displayed higher relative abundance in the winter than in other seasons. Our results emphasize the extreme seasonality of Arctic microbial eukaryotic communities driven by the light regime and nutrient availability but point to the necessity of a thorough knowledge of hydrography for full understanding of their succession and variability. Microbial eukaryotes are critically important for the functioning of marine ecosystems as primary producers (1, 2) and consumers (3, 4) of carbon, as well as maintainers of biogeochemical cycles (5-7). In Arctic waters, where marine planktonic cyanobacteria are infrequent, marine microbial eukaryotes are the predominant primary producers (8-10). In spite of their importance, our knowledge of the diversity and role of picosized (0.2 to 2 m) and nanosized (2 to 20 m) (11) eukaryotic plankton is still limited in extreme areas.High-Arctic regions are characterized by extreme seasonality in light conditions, with 24 h of sunlight in summer giving way to several months of complete darkness in winter. The cold, dark polar night period at high latitudes strongly limits the activity of autotrophic organisms, and Arctic species in general have to adjust to the timing of seasonal events (12). The few studies performed during the Arctic winter-spring transition suggest a strong seasonal response by the microbial community to irradiance (13)(14)(15). Most studies of Arctic microbial eukaryotes have so far utilized traditional identification techniques, such as microscopy, and focused on bloom-forming pelagic protists (4, 16-18). The development of molecular techniques, especially high-throughput sequencing (HTS), has made it possible to study the diversity and assemblages of pico-and nanosized eukaryotic plankton as well (19)(20)(21)(22). This has resulted in several diversity surveys of microbial eukaryotes from the Arctic Ocean and the shelf seas (23-27). Pico-and nanosized planktons are now known to govern major processes in the oceans to a larger degree than previously assumed (6,7,28,29). Furthermore, 18S ...

Comparison of coastal phytoplankton composition estimated from the V4 and V9 regions of the 18S rRNA gene with a focus on photosynthetic groups and especially Chlorophyta

“…Metabarcode analysis methods using assignation rely heavily on carefully curated public database such as PR 2 or, even better, on specifically tailored databases that include, besides public sequences, reference sequences for the environment investigated, as for example Arctic specific databases for polar environments (Comeau et al, 2011;Marquardt et al, 2016). Other approaches to analyze metabarcoding datasets do not rely on reference databases.…”

Seasonal and Interannual Changes in Ciliate and Dinoflagellate Species Assemblages in the Arctic Ocean (Amundsen Gulf, Beaufort Sea, Canada)

“…Dinoflagellates and ciliates persist over winter darkness in the Arctic (Terrado et al, 2011;Marquardt et al, 2016), but their seasonal progression is poorly understood. To resolve temporal patterns at finer taxonomic resolution, and to test for trends consistent with environmental selection among Arctic microzooplankton, we investigated samples collected from November 2007 to July 2008 during the International Polar Year Circumpolar Flaw Lead Study (IPY-CFL; Barber et al, 2010Barber et al, , 2012.…”

Proton‐pumping rhodopsins are abundantly expressed by microbial eukaryotes in a high‐Arctic fjord

“…and Gymnodinium sp.) are common throughout the Arctic (Lovejoy ; Marquardt et al ., ; Hardge et al ., ) and elsewhere (Le Bescot et al ., ), but even though the phylogeny of the dinoflagellates has been considerably improved (Orr et al ., ) the evolutionary relationships of these genera remain poorly understood (Hoppenrath, ). The abundance of Gymnodiniales mRNA (e.g., Karlodinium veneficum ) in the metatranscriptome and dominance of ‘NIF‐3A1’ in the 18S rDNA are in agreement and suggests this phylotype as the origin of both the xantho‐ and proteo‐rhodopsins.…”