Introduction

Cyanoprokaryota (Cyanobacteria) are widespread and ecologically important organisms of aquatic and terrestrial ecosystems of the Arctic. Their unique abilities to photosynthesize and fix molecular nitrogen make them a special group in production of organic matter in the water bodies and soils of high latitudes.

In Arctic water bodies, cyanoprokaryotes form dominant communities in phytoplankton and benthos. In southern parts of the Arctic, some species can cause «blooming» of the water bodies. In terrestrial habitats of high latitudes, cyanoprokaryotes can form visible growths on the surface of and in the soil. Reduced competition from higher plants allows cyanobacterial mats and films to occupy considerable areas. Cyanoprokaryotes occur on soil surfaces lacking vegetation, and on the surface of, and within cracks penetrating rocky substrata. Growth in cracks in rocks and internally amongst rock crystals provides protection against temperature changes, dehydration, and external physical influences (e.g., destruction by the wind). Cyanoprokaryotes are often the first organisms to inhabit glaciers and moraines (Kaštovská et al., 2005, 2007; Turicchia et al., 2005; Davydov, 2011). Their high abundance is seen in bryophyte communities of moist habitats along the shores of lakes, streams, pools, and the splash zone of waterfalls.

The current state of Cyanoprokaryota biodiversity has not been analyzed in the massive area (58.7 million km2) occupied by the Eurasian Arctic and Hypoarctic (Fig. 1). The studies of cyanoprokaryotes in high latitudes are problematic due to much of the region being remote. The aim of this study was to combine all available published data and results of our own research on diversity of Cyanoprokaryota in the Eurasian sector of the Arctic and Hypoarctic.

Fig. 1
figure 1

The map of cyanoprokaryotes distribution in the Arctic and Hypoarctic. Color code: violet—the southern boundary of polar desert zone, green—the southern boundary of tundra zone, red—the southern boundary of the Hypoarctic, blue dots are all locations of cyanoprokaryota records

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Within Eurasia, the Arctic territories usually include continental margins and the entire Arctic Ocean with its archipelagos and islands. Recognition of zones within northern high-latitude regions varies among authors (Polunin, 1951; Aleksandrova, 1980; Bliss, 1981; Elvebakk, 1985; Matveyeva, 1998). The division of the Arctic into High Arctic and Low Arctic is commonly accepted (Bliss, 1975). In Russian research practice, two zones are usually distinguished in the Arctic: polar deserts and tundras which divide into Arctic tundra and Subarctic tundra (Aleksandrova, 1980, 1988). The High Arctic subzone includes polar deserts and Arctic tundras, and the Low Arctic subzone comprises Subarctic tundras.

Here, we assume that the southern boundary of the Arctic corresponds to the southern boundary of the tundra zone (Aleksandrova, 1980; Walker et al., 2005) and the Arctic includes the polar deserts zone and tundra zone. The transition zone from tundra to the forest is considered Subarctic or Hypoarctic (Yurtsev, 1994). According to B.A. Yurtsev (1994), it includes typical and southern tundras, forest tundra, and the northern edge of the boreal forest. Here, we place only transitional ecotone communities of forest tundra and northern taiga in the Hypoarctic. Consequently, we accept the boundary between the northern and middle taiga as the southern border of the Hypoarctic (Yurtsev, 1994).

Historical review of studies on Cyanoprokaryota biodiversity in the Eurasian Arctic and Hypoarctic regions

The location of all regions is shown in Fig. 2. Spitsbergen (Svalbard) archipelago has the longest history of study of Cyanoprokaryota in the European sector of the Arctic. The first records were made in the late nineteenth and early twentieth centuries (Table 1). Spitsbergen archipelago has also been a focus for their role in colonization processes following glacial retreat (Kaštovská et al., 2005, 2007; Turicchia et al., 2005; Stibal et al., 2006; Kvíderová et al., 2011) including nitrogen fixation (Liengen & Olsen, 1997; Solheim et al., 2002; Zielke et al., 2002, 2005). Several species from Spitsbergen archipelago were the subject of taxonomic and biogeographic studies (Komárek et al., 2006; Strunecky et al., 2012; Richter & Matuła, 2013).

Fig. 2
figure 2

The regions included in the research: 1 Malozemelskaya tundra, 2 Bolshezemelskaya tundra, 3 Polar Urals, 4 Subpolar Urals, 5 Commander Islands, Ch Chukotka peninsula, FJL Franz Josef Land archipelago, KK Krasnoyarsk kray, KP Kamchatka peninsula, MaR Magadan region, MR Murmansk region, NSI New Siberian Islands, NZ Novaya Zemlya archipelago, RK Karelia republic, RS Sakha (Yakutia) republic, SZ Severnaya Zemlya archipelago, SV Spitsbergen archipelago, T Taimyr peninsula, Y Yamalo-Nenets Autonomous Okrug

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Table 1 Total numbers of Cyanoprokaryota species recorded from various regions of the Arctic and Hypoarctic
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There have been few psychological studies on Franz Josef Land archipelago and Novaya Zemlya archipelago (Table 1).

Murmansk region is well studied with 359 species described. This is one of the richest floras in Russia, possibly due to the long history of research in the region starting with Elfving (1895). The history of research and a combined list of species for the region are provided by Davydov (2010a).

Three hundred and twenty species have been recorded from Eastern European tundra. Several studies have examined the tundras of Bolshezemelskaya and Malozemelskaya and the Polar and Subpolar Urals (Table 1).

There have been several studies in the Asian sector of the Arctic. Soil communities in polar deserts have been studied by Patova & Belyakova (2006). At lower latitudes, soil and freshwater species are described for Taimyr Peninsula, Yamalo-Nenets Autonomous Okrug, and rivers of Yakutia. Few studies have been carried out in the Chukotka and in Magadan regions.

Literature survey and data analyses

We combined our new findings with records from our CYANOpro database (http://kpabg.ru/cyanopro/) (Melechin et al., 2013), obtained during an extensive literature analysis, in order to review Cyanoprokaryota diversity in the Eurasian Arctic and Hypoarctic. The database has free and open access to Cyanoprokaryota biodiversity data, it is accessible through the Internet and only registration is needed. For species identification, recent monographs were used (Komárek & Anagnostidis, 1998, 2005; Komárek 2013). We studied 1500 database records of cyanoprokaryotes and our data (both new and published) obtained from 1000 samples collected in terrestrial and aquatic ecosystems. We used a special program code of CYANOpro database system to filter data and select data points for the polar deserts of the Arctic and Hypoarctic.

Floristic similarity was investigated using the Sørensen index (KS) (weighted pair-group method using arithmetic averaging) in the program module GRAPHS (Nowakowskiy, 2004): KS = 2a/(a + b) + (a + c), where a is the number of species common to both sets; c is the number of species unique to the first set; and b is the number of species unique to the second set.

Estimate of the current cyanobacterial biodiversity in the Eurasian Arctic and Hypoarctic and perspectives of further studies

Comparative analysis of species composition along the latitudinal gradient from polar deserts to the Hypoarctic

Within the Eurasian sector of the Arctic and Hypoarctic, 603 species of cyanoprokaryotes were found of which 482 were in the Arctic zone. This diversity belongs to 113 genera, 38 families, and 8 orders.

In the Eurasian sector of polar deserts, 156 species of cyanoprokaryotes were noted. Most species (147) were found in the Barentz province of the polar desert zone which includes North-East Land Island in the Spitsbergen archipelago, Franz Josef Land archipelago, and the northern tip of Novaya Zemlya. Siberian province (Severnaya Zemlya archipelago, the northern tip of Taimyr) had only 45 species.

Flora of polar deserts in Spitsbergen archipelago is presently the best studied among high-latitude regions and had 118 species. Flora of Franz Josef Land, the whole territory of which is entirely within the polar desert zone, had 69 species. Species similarity between archipelagos is low (Sørensen index of 26%) with only 25 common species, most being typical hydrophytes. A more detailed study of Franz Josef Land could result in a lower floristic difference.

Franz Josef Land and Severnaya Zemlya floras are closer (Sørensen index of 33%); however, the number of common species is only 18.

As expected, the number of species increases in the less harsh conditions of the Arctic tundra. 456 species are recorded for the territories of which 129 are common to polar deserts and Arctic tundra (Sørensen index of 41%). 30 species of cyanoprokaryotes were found only in polar deserts but not in the tundra. Most of them were found in southern areas of the Hypoarctic, except for 11 species (Chroococcus obliteratus P. G. Richt., Coleodesmium wrangelii ([C. Ag.] Born. et Flah.) Borzì ex Geitl., Gomphosphaeria cordiformis (Wille) Hansg., Leptolyngbya aeruginea (Kütz. ex Hansg.) Komárek, L. gelatinosa (Voronich.) Anagn. et Komárek, Merismopedia hyalina (Ehrenb.) Kütz., Microchaete calothrichoides Hansg., Phormidium lividum Näg., Symplocastrum aurantiacum (Hansg. ex Hansg.) Anagn., Trichocoleus tenerrimus (Gom.) Anagn., Xenococcus minimus Geitl.) which were not found there. We do not consider these as typical species of polar deserts because they have a worldwide distribution.

Four hundred and twenty-eight species have been recorded from the Eurasian Hypoarctic. The floristic similarity between the tundra zone and Hypoarctic is high (Sørensen index of 65%). A high similarity is also noted between the flora of the polar deserts and the Hypoarctic (Sørensen index of 45%). 307 species are found in the Hypoarctic flora but not in the Arctic zone; a significant number (117) is found in polar deserts and probably will be discovered in the tundra zone. 190 species are found only in the Hypoarctic. Some can be described as boreal species, in particular the representatives of the genera Anabaena (A. aequalis, Anabaena augstumalis, A. catenula (Kütz.) Born. et Flah., A. cylindrica Lemm., A. verrucosa B.-Pet. et al.), Dolichospermum (D. affinis, D. circinale, D. lemmermannii), Hapalosiphon (Hapalosiphon hibernicus W. West et G. S. West, H. intricatus, H. pumilus), Rivularia (R. aquatica De-Wild., R. beccariana [De Not.] Born. et Flah., R. borealis P. G. Richt., R. haematites), as well as the species Aulosira laxa Kirchn. ex Born. et Flah., Gloeotrichia echinulata, G. pisum Thur. ex Born. et Flah., Gomphosphaeria virieuxii (Virieux) Komárek et Hind. and Woronichinia karelica Komárek et Kom.-Legn.

Comparative studies of territorial floras of the Arctic and Hypoarctic

Regions and territories within the Arctic and Eurasian Hypoarctic have received varying intensities of study. The highest number of species has been observed in the well-studied Murmansk region (408 taxa, 359 species). The high number of species is detected on Spitsbergen archipelago (314) and Bolshezemelskaya tundra (191), Karelia Republic. Taimyr peninsula (123), Malozemelskaya tundra (122), Polar Urals (89), Chukotka (84), Subpolar Urals (150), Franz Josef Land archipelago (68), Magadan region (63), Novaya Zemlya archipelago (60), Yamal peninsula (62) have been only partially studied and have lower numbers of species. The smallest number of species was found in Severnaya Zemlya archipelago (41).

The reason for the rich flora of the Murmansk region is the wide diversity of habitats and the long history of studies. Vegetation zones vary from the northern boreal forests to the southern tundra. The number of species that are similar to Spitsbergen flora is high, considering that a large part of Spitsbergen (60%) is covered by glaciers. The floristic diversity of the Spitsbergen archipelago is probably due to a wide range of environmental conditions from mountainous territories with a varied geology to large areas of lowland tundra with many small ponds. Despite the small area of Malozemelskaya tundra, there is a rich flora (122 species). Some parts of the Urals region have been well-studied. The north part (Polar Urals) has 89 species, and the southern part (Subpolar Urals) has 150 species. The species richness could be explained by diverse mountain conditions (considerable altitudinal range and diverse landscapes), and the relatively low latitude of the Urals regions. Taimyr has a large number of species but an increase in species richness would be expected after more detailed studies as in addition to the large area it has several vegetation zones.

Similarities of species composition between different regions are generally quite low (Fig. 3). A high similarity (Sørensen index of >50%) only occurs for relatively well-studied flora of the Murmansk region and Spitsbergen archipelago (54%), and for Franz Josef Land and Novaya Zemlya (51%). The similarities between floras of Polar Urals and Subpolar Urals (30%), Polar Urals and Bolshezemelskaya tundra (43%), and Bolshezemelskaya tundra and Taimyr (38%) may be due to their similar geology.

Fig. 3
figure 3

A complete graph of similarity between Cyanoprokaryota floras in studied areas of the Arctic (gray circle) and Hypoarctic (white circle) (Sørensen index). For clustering, the mean distance between elements of each cluster was used with weighted pair-group method using arithmetic averaging, numbers on the ridges are similarity index shown in percentages where BT Bolshezemelskaya tundra, Ch Chukotka, FJL Franz Josef Land archipelago, MaR Magadan region, MR Murmansk region, MT Malozemelskaya tundra, NZ Novaya Zemlya archipelago, PU Polar Urals, SPU Subpolar Ural, SV Spitsbergen archipelago, SZ Severnaya Zemlya archipelago, T Taimyr peninsula, Y Yamal peninsula

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The distribution of species amongst habitats

There are two ecological groups of species according to habitat type: aquatic and terrestrial. The latter can be sub-divided into subaerophytic (at the margins between aquatic and aerophytic habitats) and aerophytic (inhabitants of rocky substrates and soil surfaces).

Aquatic habitats

A reduction of species diversity in freshwater waterbodies Cyanoprokaryota from south to north is one of the main environmental features of high latitudes. This happens since the majority of water bodies in the polar desert zone of the Arctic are oligotrophic and also ultra-oligotrophic as they have a glacial origin and low temperature in the summer and the short vegetation period. Under such conditions, the species diversity and biomass of cyanoprokaryotes in plankton and benthos is low. The most common planktonic species are shown in Table 2.

Table 2 The typical species of aquatic habitats in various regions of Arctic and Hypoarctic
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There is low species diversity in typical planktonic genera (Anabaena, Aphanizomenon, Dolichospermum) in floras of high-latitude regions of Spitsbergen, Franz Josef Land and Novaya Zemlya archipelagos but their diversity increases markedly in the subarctic tundra. For example, a typical widespread species, Aphanizomenon flos-aquae, has not yet been found in any Arctic archipelagos (Spitsbergen, Franz Josef Land and Novaya Zemlya, Severnaya Zemlya) but it is frequently observed in the more southern tundra and Hypoarctic territories (e.g., Murmansk region, Malozemelskaya tundra and Bolshezemelskaya tundra, Taimyr) where it often colors water with its vigorous growths.

Plankton of large lakes of polar deserts usually includes tychoplanktonic species from Pseudanabaena, Leptolyngbya, Jaaginema, and Oscillatoria. Cyanoprokaryota of benthic habitats in Arctic and Hypoarctic lakes are more diverse and abundant. One of the most common benthic species in the lakes of high latitudes on Spitsbergen archipelago, and probably in other Arctic territories, is Oscillatoria tenuis (Table 2). Benthic mats formed by Phormidium uncinatum are also frequent.

In benthos of more southern lakes of the tundra zone species of Tolypothrix and Hapalosiphon are most frequent, whilst in mountain lakes these are replaced by species of Scytonema and Chamaesiphon.

Rivers at high latitudes are fed by meltwater from glaciers and snow fields. Upper reaches of rivers are cold, fast, and have large amounts of suspended mineral particles. These are extremely unfavorable conditions for development of cyanoprokaryotes. Towards the lower reaches, river flow slows but transparency and temperature often remain low. Cyanoprokaryota communities in rivers have similar species composition to those in smaller streams (Table 2).

Watersheds of more southern rivers are located in waterlogged boggy areas, so the transparency of the water is low due to high concentrations of humic acids. Turbulent rapids are often common for Hypoarctic and Arctic rivers. High rocky banks are typical of rivers in the mountains. Epilithon in these diverse rivers comprises species of Merismopedia, Microcystis, Coelospherium, Chamaesiphon, Stigonema, Tolypothrix, and Rivularia (Table 2).

In large rivers, massive growth of cyanoprokaryotes is only observed in their estuaries where phytoplankton blooms are caused by species of Aphanizomenon, Dolichospermum, Nodularia, and Phormidium.

Arctic streams are divided into two types: fast and slow. Fast streams are fed by glaciers. These have water that is cloudy with suspended sediment and only a few degrees above freezing. Algal communities are restricted to epilithon that forms mucous films on the surface of large boulders. Diversity is low being from 1 to 8 species (Table 2).

A greater diversity is found in slow streams. Phormidium uncinatum is the first alga to appear in upper reaches of slow streams which usually begin near snowfields. Further downstream species of Leptolyngbya appear. Small pebbles in the stream bed form a good habitat for Dichothrix gypsophila. This is also common in ephemeral ponds and small lakes.

Epilithon in streams also includes species of Ammatoidea, Aphanocapsa, Chamaesiphon, and Tolypothrix (Table 2). The bed of small streams is often covered by Microcoleus autumnalis which is one of the most common Arctic species.

Streams of southern Hypoarctic regions that are fed by ground springs have a high transparency. These are a good habitat for Tolypothrix tenuis, T. distorta, Nostoc coeruleum, Calothrix braunii Born. et Flah., C. clavata, Calothrix parietina, Dichothrix gypsophila, Gloeotrichia pisum and Rivularia haematites.

Terrestrial habitats

Terrestrial habitats support a greater diversity and abundance of cyanoprokaryotes with progression from South to North. A decrease in competition from higher plants and an increase in the range of ecological niches could explain this.

Subaerophytic habitats

These are transitional between aquatic and aerophytic habitats, typically being banks of water bodies, flooded areas of slopes and terraces and moss tundra wetlands. They are the most frequently occurring habitats in high latitudes and support the highest diversity of cyanoprokaryotes. Extensive mats (from 2 to 3 cm thick) are formed at the bottom of widespread, shallow, ephemeral lakes. These are dominated by Phormidium uncinatum which forms an upper layer and Leptolyngbya cf. gracillima and Pseudanabaena cf. minima, which form a bottom layer (Table 3). Mats dominated by Petalonema species (P. alatum and P. crustaceum) are less frequent.

Table 3 The typical species of transitional habitats between aquatic and aerophytic environments in various regions of the Arctic and Hypoarctic
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Continuous snow melt during summer produces abundant runoff which results in waterlogging of upper soil horizons under permafrost conditions. Those habitats are called seepage (Komárek et al., 2012). Here, Gloeocapsa kuetzingiana, G. sanguinea, G. violacea and species that are often recorded in puddles and streams (Chroococcus turgidus, Microcoleus autumnalis, Oscillatoria tenuis, Phormidium kuetzingianum, P. uncinatum) are found.

Epiphytic on mosses in waterlogged moss tundra are Chroococcus turgidus, Symplocastrum friesii, Hapalosiphon pumilus, Fischerella muscicola, Aphanocapsa muscicola, Scytonema ocellatum, S. hofmannii, Microcoleus vaginatus, Nostoc punctiforme.

Nostoc commune is probably the most common species for all tundra habitats and especially in wet tundra. It is one of the most common species of the Arctic which can be found everywhere due to its adaptability to a wide range of habitats from bare ground of glacier nunataks to the bottom of rocky outcrops and small ponds. In wet moss tundras, its colonies can form a continuous cover over several square meters. Nostoc colonies can cover moss surfaces as well as grow within moss cushions. They could also be found in small ponds and water filled depressions. The study on genetic variation using 16S rRNA sequencing and AFLP methods of different colonies in the studied regions confirmed that all the specimens belong to Nostoc commune (Patova et al., 2015).

Aerophytic habitats

Aerophytic cyanoprokaryotes are inhabitants of rocky substrates and soil surfaces. Elevated rocky surfaces of different origins and geology are widespread in the Arctic and Hypoarctic. Combined with a lack of competition from lichens and vascular plants, this stimulates species richness of cyanoprokaryotes. Greatest abundance is observed on wet rocks receiving water from snow fields. Loose rocks are easily drained and remain dry most of the summer which makes them a hostile environment which is not colonized by cyanoprokaryotes. Under typical Arctic conditions, the most common thin crusts on wet rocks are of species of Gloeocapsa and Chroococcus (Table 4). In Hypoarctic regions, the most frequent crusts are of Stigonema ocellatum, S. minutum, and S. informe with associated Gloeocapsopsis magma and Gloeocapsa violascea.

Table 4 The typical species of aerophytic habitats in various regions of Arctic and Hypoarctic
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Cyanoprokaryota crusts on soil surfaces vary in composition and can occupy large areas due to the high occurrence of bare spots in the Arctic regions. Those habitats are from 1 to 10 m2 or 20–90% of the area in the communities. Typical species of wet soils are Aphanocapsa grevillei, Leptolyngbya boryana, Microcoleus favosus, M. vaginatus, Nostoc commune, N. punctiforme, Petalonema crustaceum, Stigonema ocellatum, S. minutum, Scytonema ocellatum, Tolypothrix tenuis, and T. distorta.

Species often found at relatively high abundance in soils are Chroococcus cohaerens, Cyanothece aeruginosa, Desmonostoc muscorum, Kamptonema animale, Leptolyngbya boryana, Leptolyngbya foveolarum, Phormidium ambiguum, Nostoc punctiforme, N. linckia, and N. microscopicum. In ornithogenic habitats, such as downslope from bird colonies, species-richness is 4–5 species, but Microcoleus autumnalis is always found.

The presently known diversity of cyanoprokaryotes in the Eurasian Arctic and Hypoarctic comprises 603 species (Table 5). The Arctic has 80% of this total. In the Hypoarctic, 71% are observed. This could be attributed to the smaller area and the reduced range of environmental conditions (Fig. 2).

Table 5 The numbers of Cyanoprokaryota species in different zones
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89% of species in the Arctic are found in the tundra zone while polar deserts have only 32%. The diversity of polar deserts in comparison with the total Arctic and Hypoarctic species is only 26%.

The harsh environment of polar deserts supports fewer species than Arctic tundra in which 456 species have been observed. This increased diversity can be attributed to the wider range of habitats that are favorable for cyanoprokaryotes.

The species richness within subclasses is similar in all zones. Oscillatoriophycidae (40%) is dominant in the total species list whilst Synechococcophycideae (32%) and Nostocophycideae (27%) are similar. The proportion of Nostocophycideae species increases in Hypoarctic. In the tundra zone and the Hypoarctic, species richness within orders is greatest in the Synechococcales and Nostocales. In polar deserts, there is an increase in the proportion of Chroococcales and a decrease in the proportion of Nostocales (Fig. 4). This is due to the low diversity of Anabaena and Dolichospermum and the increase in diversity of Gloeocapsa and Chroococcus species.

Fig. 4
figure 4

Comparison of species richness within each order of cyanobacteria in the two Arctic zones and the Hypoarctic

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Undoubtedly, Cyanoprokaryota floras of the Arctic and Hypoarctic are still unevenly and incompletely studied. Murmansk region (359 species) and Spitsbergen archipelago (314 species) are the most fully studied. They also have the greatest similarity of species composition (Sørensen index of >50%). Relatively well-studied floras of other regions have 100–300 species as well as high similarity in species composition. It can be predicted that important additions to knowledge of species occurrence for all studied regions will result from an expansion of research to new areas. A significant increase in the knowledge of diversity of Arctic Cyanoprokaryota would also result from the application of the techniques of molecular genetics to investigate morphologically similar species and others which are difficult to place within the current taxonomic system. Some researchers discuss a possible endemism of Arctic and bipolar species (e.g., Komárek et al., 2012).

Subaerophytic cyanoprokaryotes had the highest species diversity (300 species) of all ecological groups. Cyanoprokaryota diversity changes differently for aquatic and terrestrial environments in a latitudinal gradient from polar deserts to Hypoarctic tundra. One of the main observed environmental patterns is a notable reduction in diversity of typical aquatic species from south to north, and in contrast, an increase in diversity of subaerophytic and aerophytic species in the north. An increasing area of the terrestrial ecosystem is occupied by cyanoprokaryotes with progression from the Hypoarctic to polar deserts. The main reason appears to be the reduced competition from higher plants.

The most widespread species of the Arctic and Hypoarctic are indicated in the species lists given in Tables 2, 3, and 4.

Spitsbergen and Franz Josef Land archipelagos and Polar and Subpolar Urals are typical mountain areas of the Arctic. Cyanoprokaryota floras of these regions are characterized by epilithic species of Gloeocapsa and Chroococcus as well as by the same species composition of subaerophytic cyanoprokaryotes and the high number of species growing on primitive soils (species of Leptolyngbya spp., Pseudanabaena spp., Microcoleus spp.).

Perspectives and future directions

The diversity of Cyanoprokaryotes in the Eurasian part of the Arctic and Hypoarctic is similar to that of the Antarctic and sub-Antarctic islands (537 species) (https://data.aad.gov.au), of Sweden (558) and of the Czech Republic (505), all being regions where detailed studies have been made (Willen, 2001; Kaštovský et al., 2009). However, these regions all have less environmental diversity than the studied regions of the Arctic and Hypoarctic. We suggest that further research on Cyanoprokaryota in the Arctic and Hypoarctic, including modern molecular studies, would significantly increase the known species and indicate which of these are endemic.

This review has indicated the high diversity of Cyanoprokaryota in the Arctic and Hypoarctic and that species occupy a wide range of aquatic and terrestrial habitats where they form dominant communities. To the south, the pattern is reversed and aquatic cyanoprokaryotes grow in abundance and cause blooms but in terrestrial habitats cyanoprokaryotes are of greatly reduced importance.

A special feature of the Eurasian Arctic and Hypoarctic is the limited number of dominant species. However, these are not special species for high-latitude regions as they are also found in the southern boreal zone.

Further study is required of the ecological preferences of individual species and their role in the formation of microbial communities in aquatic and terrestrial ecosystems of high latitudes. An integrated study of Cyanoprokaryota biodiversity, ecology, and geography in the Arctic and Hypoarctic will enlarge knowledge of the structural and functional diversity of ecosystems and history of biota in the Eurasian region.