Snow algae communities in Antarctica: metabolic and taxonomic composition

Abstract

Snow algae are found in snowfields across cold regions of the planet, forming highly visible red and green patches below and on the snow surface. In Antarctica, they contribute significantly to terrestrial net primary productivity due to the paucity of land plants, but our knowledge of these communities is limited. Here we provide the first description of the metabolic and species diversity of green and red snow algae communities from four locations in Ryder Bay (Adelaide Island, 68°S), Antarctic Peninsula. During the 2015 austral summer season, we collected samples to measure the metabolic composition of snow algae communities and determined the species composition of these communities using metabarcoding. Green communities were protein-rich, had a high chlorophyll content and contained many metabolites associated with nitrogen and amino acid metabolism. Red communities had a higher carotenoid content and contained more metabolites associated with carbohydrate and fatty acid metabolism. Chloromonas, Chlamydomonas and Chlorella were found in green blooms but only Chloromonas was detected in red blooms. Both communities also contained bacteria, protists and fungi. These data show the complexity and variation within snow algae communities in Antarctica and provide initial insights into the contribution they make to ecosystem functioning.

Keywords: Antarctica; bacteria; community composition; cryophilic; fungi; metabarcoding; metabolomics; snow algae.

Figure 1

Representative image of snow algal blooms (red‐dominant foreground, green‐dominant midground) in January 2015 on Léonie Island, Ryder Bay, Antarctic Peninsula (see Supporting Information Table S1 for details). Note person in midground for scale.

Figure 2

Metabolic fingerprinting (FT‐IR) reveals differences between green and red blooms. Score scatter plot (a) from principal component analysis of FT‐IR wavenumber intensities of green (circles, n = 30) and red (squares, n = 40) snow algae communities collected from four locations adjacent to the Antarctic Peninsula (Rothera Point (RP), Anchorage Island (AN), Léonie Island (LE) and Lagoon Island (LA)) during January and February 2015 (austral summer). The score contribution plot (b) indicates which FT‐IR wavenumbers differ the most between green (protein, amide I, II) and red (lipids, lipid esters, polysaccharides) snow algae communities along PC1 and PC2.

Figure 3

Lipid content of snow algae blooms. Total triacylglycerides (TAGs), membrane lipids and free fatty acids (as C16 equivalent) are expressed as both mg g⁻¹ dry cell mass (DCM; a, c, e) and mg l⁻¹ snowmelt (b, d, f) from green and red snow algae communities collected from four locations adjacent to the Antarctic Peninsula (Rothera Point, Anchorage Island, Léonie Island and Lagoon Island) during January and February 2015 (austral summer). Data are mean ± SD. Total green and red sample sizes (n) are: RP 4, 3; AN 3, 7; LE 1, 2; LG 3, 3. Statistical differences (ANOVA) between green and red communities within a location are denoted by: *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001.

Figure 4

Metabolic profiling (GC‐MS) reveals differences between green and red blooms. Score scatter plot (a) from principal component analysis (PCA) of putatively identified metabolite intensities (GC‐MS) of green (circles, n = 11) and red (squares, n = 14) snow algae communities collected from four locations adjacent to the Antarctic Peninsula (Rothera Point (RP), Anchorage Island (AN), Léonie Island (LE) and Lagoon Island (LA)) during January and February 2015 (austral summer). The score contribution plot (b) values (top 20) are ranked in order of importance and are positive if they contribute towards PCA loading plots for the green snow algae communities and negative if they contribute towards the red snow algae communities. The full list of metabolites is presented in Supporting Information Table S4.

Figure 5

Taxonomic composition of snow algae blooms. Per cent contribution of taxonomic assignments for 99% aligned operational taxonomic units (OTUs) for 16S rRNA and 18S ITS1 sequences in green and red snow algae communities from Ryder Bay, Antarctica, during January and February 2015 (austral summer). Per cent contribution values are the mean relative abundance of the taxa as a percentage of total sequences with < 0.5% abundance and are classified at the (a, b) class or (c, d) genus level. Low abundance OTU values are the sum of the percentages for taxa identified below 0.5% contribution. All values are the mean of n = 5 (green community sites) or n = 6 (red community sites). SAR, ‘stramenopiles, alveolata, rhizaria’. Detailed OTU read numbers, per cent contributions and statistics are presented in Supporting Information Tables S6–S8.