Comparison of wintertime eukaryotic community from sea ice and open water in the Baltic Sea, based on sequencing of the 18S rRNA gene

Abstract

The Baltic Sea is one of the world's largest brackish water basins and is traditionally considered to be species poor. Here, we assessed the diversity of the nanosized eukaryotic microbial wintertime community, using molecular ecological methods based on sequencing of small-subunit ribosomal RNA gene clone libraries. The results demonstrate that a rich community of small eukaryotes inhabits the Baltic Sea ice and water during winter. The community was dominated by alveolates and stramenopiles. Ciliates and cercozoans were the richest groups present, while in contrast to previous studies, diatoms showed a lower richness than expected. Furthermore, fungi and parasitic Syndiniales were present both in the water and in the sea ice. Some of the organisms in the sea-ice community were active, based on the RNA data, but a number of organisms were inactive or remnants from the freezing process. The results demonstrate that the sea-ice communities in the Baltic Sea are highly diverse and that water and ice of diVerent ages include diVerent protistan assemblages. Our study emphasizes the potential loss in biodiversity through diminishing ice cover as a result of climate change.

Mesoscale distribution and functional diversity of picoeukaryotes in the first-year sea ice of the Canadian Arctic

“…Picoeukaryotes are among the least known protistan groups in the sea ice. The first studies on the diversity of sea-ice protists (not only picoeukaryotes) have shown sea-ice communities to consist of various phylotypes (Eddie et al, 2010;Bachy et al, 2011;Majaneva et al, 2012;Comeau et al, 2013). Our study complements these recent results with the first report on the quantitative distribution of particular groups of picoeukaryotes in first-year sea ice, including percentage of cells actively feeding by phagocytosis.…”

“…The most important are: group coverage by a probe (percentage of sequences within a group that are targeted by the probe), and hits outside a group (Amann and Fuchs, 2008). All but two probes used in our study has coverage 480% (Supplementary Table S1), and all but one (Bolido02) matches all sequences retrieved from sea ice in the previous studies (Majaneva et al, 2012). This indicates that use of CARD-FISH technique enabled reliable estimation of numbers of most of the investigated groups, providing baseline data on the distribution and relative importance of these groups in the sea ice.…”

“…Cryptophytes were the second most numerous group (Figure 4). Cryptophyte phylotypes related to Teleaulax and Hemiselmis were found in first-year sea ice in the Canadian Beaufort Sea (Comeau et al, 2013) and the Baltic Sea (Majaneva et al, 2012), but not in multiyear ice close to the North Pole (Bachy et al, 2011). Sequences of cryptophytes have been recovered from size-fractionated (0.2-3 mm) Arctic waters (Terrado et al, 2011).…”

“…Chlorophytes and cryptophytes were the most numerous groups (Figure 4). Sequences of chlorophytes were also retrieved from multi-year sea ice close to the North Pole (Bachy et al, 2011), and first-year sea ice in the Beaufort Sea (Eddie et al, 2010;Comeau et al, 2013) and the Baltic Sea (Majaneva et al, 2012). These phylotypes were related to Chlamydomonas, Mantoniella, Bathycoccus, Pyramimonas and Microsomonas.…”

“…In result, they have received substantially less attention than sea-ice diatoms, and their composition and role are largely understudied. The phylogenetic diversity of pico-(cell size o3 mm) and nano-(cells size 3-20 mm) eukarytoes in the sea ice has been studied only recently (Eddie et al, 2010;Bachy et al, 2011;Majaneva et al, 2012;Comeau et al, 2013), but reliable identification and enumeration is still lacking. Knowledge on the distribution and abundance of sea-ice protists is essential to understand and predict possible changes in microbial communities that will have profound impacts on Arctic marine food webs (Davidson et al, 2010).…”