The region experienced a strong warming period throughout the second half of the 20 th century that resulted in increased snowmelt, and at present is undergoing a period of temporary cooling (Turner et al., 2009, 2016). The Antarctic Peninsula has an extremely variable climate. Significantly, recent studies of snow algae in the High Arctic have shown that they can alter the albedo of the snow, with darker snow surfaces during red phase algal blooms increasing the local rate of snowmelt (Lutz et al., 2016 Cook et al., 2017 Ganey et al., 2017 Stibal et al., 2017). More widely, these algae play a key role in nutrient dynamics, assimilating nutrients deposited from bird colonies which, as a result of snowmelt, are leached with their associated microbial community into adjacent terrestrial or marine environments, where they support food chains (Dierssen et al., 2002 Hodson et al., 2008 Boetius et al., 2015). Furthermore, the contribution made by snow algae to terrestrial ecosystem productivity in the Antarctic is likely to be higher than that in the Arctic and other alpine regions, because algal blooms in these other regions tend to be more patchy and occur close to other well-established and extensive vegetated areas. If these measurements are typical of terrestrial communities more widely in Antarctica, and considering that a single snow algal ‘bloom’ on the peninsula can cover tens to hundreds of square metres, snow algae are potentially one of the region's most significant photosynthetic primary producers, substantially increasing the known area of land occupied by primary producers in Antarctica. ( 2011) found that areas of snow algae and terrestrial mats in Antarctica could be identified in satellite images in combination with ground-truthing. Many snow algal communities consist of either a vegetative stage, seen as green patches in the snow, with Chloromonas and Chlamydomonas species frequently being the major algal taxa, or an encystment phase (which may also be vegetative), in which the cells have accumulated the keto-carotenoid astaxanthin, giving rise to red snow patches (Hoham & Duval, 2001 Komárek & Nedbalová, 2007 De Wever et al., 2009 Leya, 2013). Snow algae blooms are often well developed in coastal snowfields as highly visible red and green patches below and on the snow surface where liquid water is present (Fogg, 1967 Broady, 1996 Müller et al., 1998). However, the actual area of cover by autotrophs may be much higher, as ground-truthing of satellite imagery has revealed that in many places vegetation comprises not only patches of bryophytes, lichens and higher plants on exposed ground, but also snow algae. For example, although the Antarctic Peninsula is the most vegetated region of Antarctica, only 1.34% of exposed ground has plant cover (Fretwell et al., 2011 Burton-Johnson et al., 2016). But even here, only a small proportion of this exposed area is vegetated. Terrestrial life in Antarctica is largely found on the estimated 0.18% of the continent's surface that is ice-free for at least part of the year (Burton-Johnson et al., 2016 Convey, 2017). 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.Both communities also contained bacteria, protists and fungi. Chloromonas, Chlamydomonas and Chlorella were found in green blooms but only Chloromonas was detected in red blooms. Red communities had a higher carotenoid content and contained more metabolites associated with carbohydrate and fatty acid metabolism. Green communities were protein-rich, had a high chlorophyll content and contained many metabolites associated with nitrogen and amino acid metabolism.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.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. 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. 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.
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