Synechococcus in the Atlantic Gateway to the Arctic Ocean

Abstract

Increasing temperatures, with pronounced effects at high latitudes, have raised questions about potential changes in species composition, as well as possible increased importance of small-celled phytoplankton in marine systems. In this study, we mapped out one of the smallest and globally most widespread primary producers, the picocyanobacterium Synechococcus, within the Atlantic inflow to the Arctic Ocean. In contrast to the general understanding that Synechococcus is almost absent in polar oceans due to low temperatures, we encountered high abundances (up to 21,000 cells mL −1) at 79 • N, and documented their presence as far north as 82.5 • N. Covering an annual cycle in 2014, we found that during autumn and winter, Synechococcus was often more abundant than picoeukaryotes, which usually dominate the picophytoplankton communities in the Arctic. Synechococcus community composition shifted from a quite high genetic diversity during the spring bloom to a clear dominance of two specific operational taxonomic units (OTUs) in autumn and winter. We observed abundances higher than 1000 cells mL −1 in water colder than 2 • C at seven distinct stations and size-fractionation experiments demonstrated a net growth of Synechococcus at 2 • C in the absence of nano-sized grazers at certain periods of the year. Phylogenetic analysis of petB sequences demonstrated that these high latitude Synechococcus group within the previously described cold-adapted clades I and IV, but also contributed to unveil novel genetic diversity, especially within clade I.

Models of Plankton Community Changes during a Warm Water Anomaly in Arctic Waters Show Altered Trophic Pathways with Minimal Changes in Carbon Export

“…Picoplankton and flagellates have been observed in sedimenting matter for the last 30 years: Synechococcus was a major contributor to fluxes to the deep sea (Lochte and Turley, 1988) and has been detected in the South Pacific (Waite et al, 2000), tropical Pacific (Stukel et al, 2013) and in equatorial Pacific, Atlantic and Indian Oceans (e.g., Lampitt et al, 1993). High abundance of Synechococcus has been recently reported for the eastern Fram Strait, included here as cells <10 µm (Paulsen et al, 2016). Similarly, the ubiquitous Micromonas sp.…”

Changes in Marine Prokaryote Composition with Season and Depth Over an Arctic Polar Year

“…Samples (25-50 L) representative of the water column profile were collected from a range of water masses (defined in Paulsen et al, 2016) between 1m and 1000 m (Table 1) using Niskin bottles mounted on a rosette deployed from the vessels. Water samples were filtered through 0.22 µm Sterivex Filter Units (Merck-Millipore, MA, USA) via a peristaltic pump and frozen at −80 • C immediately.…”

Heterotrophic nanoflagellate grazing facilitates subarctic Atlantic spring bloom development

“…The filters were immediately frozen and stored at -80 • C until nucleic acid extraction. DNA and RNA were extracted simultaneously using the AllPrep DNA/RNA Mini Kit (Qiagen, Hilden, Germany) according to manufacturer's instructions with modifications for extraction from Sterivex filters as in Paulsen et al (2016). RNA was subsequently treated with the DNAfree DNA Removal kit (Invitrogen, CA, USA) and reverse transcribed using the SuperScript III First-Strand Synthesis System for RT-PCR (Invitrogen).…”

“…We also found this group to dominate when chl a concentrations were high (i.e., DCM samples at St. 4), while they contributed only marginally (<0.1%) to the total bacterial community in the remaining fjord and particularly little in the rivers (Figure 8). Cyanobacteria were relatively abundant in the glacial runoff and can be considered as freshwater tracer, since marine cyanobacteria are usually not found in these Arctic regions (Paulsen et al, 2016). The bacterial communities in the rivers were highly specific to each of them (Figure 8), which we suggest is due to their difference in origin and catchment area; close connection (0.5 km) to the Greenland Ice Sheet (R1), longer distance (2 km) from smaller local glacier (R2), and the lowland vegetation rich river with lake connection (R3).…”