Biodiversity of periphytic cyanobacteria and algae assemblages in polar region: a case study of the vicinity of Arctowski Polish Antarctic Station (King George Island, Antarctica)

Antarctica is a territory not subjected to a state sovereignty. It is polar and subpolar area in the southern hemisphere, which consists of the Antarctic continent and the surrounding seas with many islands. Antarctica is an area important for strategic reasons due to numerous mineral resources, which for many countries are sufficient and often the only reason for territorial claims to these areas (Symonides 2008; Zawidzka-Łojek 2018). The political and legal status of Antarctica was determined by the Antarctic Treaty, adopted in 1959 in Washington (Antarctic Treaty System, ATS, 1961), regulating activities in this region. Under the provisions of the Treaty, Antarctica may be used only for peaceful purposes. In particular, all military activities or the creation of military bases are prohibited (Article 1). Treaty provides freedom of the scientific investigations and cooperation in this field, as well as exchange of information on research plans in Antarctica; exchange of scientific personnel, exchange of data and results of scientific observations in Antarctica and free access to them (Articles 2 and 3). According to the provisions of the Treaty, no State may claim rights to territorial sovereignty in Antarctica (Article 4). Additional international agreements regulating the legal status and activities in the Antarctic area are the Protocol on Environmental Protection to the Antarctic Treaty signed in Madrid on October 4, 1991, Convention on the protection of Antarctic seals signed in London on June 1, 1972 and Convention on the conservation of Antarctic marine living resources signed in Canberra on May 20, 1980 (Marciniak 2017; Świątecki et al. 2019).

Antarctica is characterized by a natural uniqueness, but also a progressive degradation of these areas caused mainly by climate change (Ciechanowicz-McLean 2017). For this reason, numerous scientific investigations are conducted in these areas, especially because of the need to protect them, which indicate their progressive degeneration due to a constant increase in temperature (Bosello et al. 2007; Cannone et al. 2018; Szafraniec 2018; Lowry et al. 2019; Świątecki et al. 2019). In the field of biological research, the main topics are marine and land biology, paleontology and monitoring of selected groups of flora and fauna (Rakusa-Suszczewski 2005). A special place of polar research is the area of King George Island, where the station named after Henryk Arctowski in the area of the Ecology Glacier is situated. This area is a kind of "hot spot" of global climate change, allows to track, among others the deglaciation process and its impact on the functioning of the polar ecosystem (Świątecki et al. 2012). Recently, the microbiological and algological studies have become very important, and they focus on determining the structural and functional characteristics of these small-sized groups of organisms. Organisms living in these areas are characterized by unique properties, including high resistance to extreme environmental factors such as low temperature, ultraviolet radiation, drying, low availability of nutrients (Grzesiak et al. 2015; Gawor et al. 2016; Grzesiak 2017). Microorganisms taken out of the melting water from the foreland of the glacier usually form heterogeneous microbial mats in the watercourses. In addition to prokaryotic microorganisms and single and multicellular algae, the presence of numerous species of protozoans, crustacean zooplankton, nematodes and tardigrades has been observed (Mieczan 2013).

The basis of microfilm mats is often composed of organic and mineral matter constituting a habitat for cyanobacteria and periphytic algae. The same matter forms a structural system of mats in streams and small water bodies located in the vicinity of the glacier. The living organisms are sensitive to environmental factors, i.e. temperature, type of substrate, oxygenation, nutrient content. In addition, the water current is very important because it facilitates immigration and subsequent colonization of periphytic algae, as well as stimulates physiological processes, including nutrient uptake and photosynthesis at higher velocities (Biggs 2000; Stevenson et al. 2006; Szabo et al. 2007; Komulaynen 2009; Zębek 2013). Thus, cyanobacteria and periphytic algae become good indicators of changes in the aquatic environment in the foreland of the glacier. We hypothesized that the changes in environmental conditions of glacier region affect the growth and diversity of periphytic assemblages inhabiting the microbial mats in streams and small water bodies. The aim of the study was to describe the diversity of periphytic cyanobacteria and algae assemblages inhabiting the microbial mats in streams and small water bodies in the vicinity of Arctowski Polish Antarctic Station (King George Island, Antarctica). We also determined the relationships between periphytic cyanobacteria and algae and physiochemical water parameters because these are important factors in the creation of suitable environmental conditions for their growth and development.

Ecology Glacier is situated at the western shore of Admiralty Bay in the Antarctic Specially Protected Area, on King George Island, South Shetland Archipelago, Antarctica (Fig. 1). It is subjected to annual surface snow melt like other glaciers in the vicinity (Braun and Gossmann 2002). The studies were carried out in the vicinity of this glacier (Fig. 2). Samples were taken in the Antarctic summer (March/April) 2019 at twenty sites in streams, S (1–15) and small water bodies, SWB (1–5) (Fig. 2, Table 1). Streams were located on the slope of Upłaz moraine, from the south and north side moraine of the Ecology Glacier, petrified forest and as an inflow to the drinking water reservoir. Small water bodies included the reservoir system at the ornithological site (penguin) and at the lateral moraine of the glacier (southern).

The microbial mats were taken from mineral and organic substrates from the streams and small water bodies. The samples were rinsed and preserved using Lugol and formaldehyde solutions. A total of 20 samples were collected. Additionally, the mat samples were taken for analyses of hydration degree using a flat mesh made of metal with an area of 5 cm². The mat was trimmed with scissors and placed in a pre-weighed 6 cm diameter Petri dish. In the laboratory, each Petri dish with the mat was weighed (wet weight), and then, it was dried at 50°C overnight to constant weight. After drying, the dry mat was weighed (dry weight). The percentage of water (% hydration) in each mat was then calculated. The basic physical and chemical water parameters were measured directly at the sampling sites. The surface water temperature, conductivity, dissolved oxygen (DO) and pH were measured in situ at the sampling sites using the WTW GmbH (Germany) equipment. The concentration of nutrients (TN, N-NH₄, TP and P-PO₄) was measured in the laboratory using a NOVA 400 spectrophotometer (Merck).

Periphytic cyanobacteria and algae from the mats were analyzed in this study. The mats were characterized by a layered structure inhabiting by filamentous and colonial cyanobacteria and chlorophytes forming the natural substrate for diatoms. The samples were shaken carefully in distilled water to separate these algae (including diatoms). Qualitative and quantitative determinations were performed with an Alphaphot YS2 optical microscope at magnifications of 100 ×, 200 ×, 400 × and 1000 ×. Diatom preparations followed the standard procedures described by Battarbee (1979). Cyanobacteria and algae biomass was calculated based on biovolume measurements by comparing with their geometric shapes (Napiórkowska-Krzebietke and Kobos 2016). The mean biomass was calculated for 10 individuals of each periphytic cyanobacteria and algae species and expressed in mg cm⁻².

Biodiversity of assemblages included species richness, and diversity indices: Shannon index (Shannon 1948) and evenness (Pielou 1966) which were calculated based on biomass of individual taxa. Dominance of cyanobacteria and algae species was classified according to their relative biomass (%) and divided into 5 classes (class I—0–20%, class II—21–40%, class III—41–60%, class IV—61–80%, class V—81–100% of the total biomass). Biomass of periphytic cyanobacteria and algae groups and dominant species were correlated with physical and chemical water parameters (water temperature, pH, conductivity, TN, N-NH₄, TP and P-PO₄) using nonparametric methods because these data are not normally distributed.

The analyses of difference in taxonomic structure of all mats were performed by the use of cluster analysis based on a percent similarity within Multivariate Statistical Package (MVSP) and Non-Metric Multidimensional Scaling (NMDS) based on Bray–Curtis distance. To reduce the number of variables, a forward selection procedure was performed using the Monte Carlo test with 999 permutations. Relationships were confirmed by calculating Spearman’s rank correlation coefficient (p < 0.05) with STATISTICA version 8, and then with the canonical correspondence analysis (CCA). All parameters were standardized using log (x + 1)-transformation. Response data were compositional and had a gradient 1.6 SD units long, thus, such a unimodal method could be used. Finally, these relationships were presented on a biplots graph using Canocco for Windows 5.0 software.

According to the general provisions of international law, the natural resources of this region may only be used for peaceful and scientific purposes (Antarctic Treaty 1959). These resources are all the more valuable due to their uniqueness and therefore should be subject to special protection (The Protocol on Environmental Protection to the Antarctic Treaty signed in Madrid on October 4, 1991; Convention on the protection of Antarctic seals signed in London on June 1, 1972; Convention on the conservation of Antarctic marine living resources signed in Canberra on May 20, 1980; Marciniak 2017; Świątecki et al. 2019). In the doctrine of international law, the protection of these resources should be in accordance with the principle of sustainable development, i.e. in such a way that they can be used by modern generations and at the same time remain for future generations. It is therefore important to prevent pollution and degradation of these natural resources, the more so as Antarctica's management system is solely based on the environment (Nowlan 2001; Hemmings 2010). Especially after the entry into force of the Madrid Protocol, some authors believe that the principles governing the Antarctic legal regime have in fact acquired an "ecological vector" (Rothwell 2000; Hemmings and Kriwoken 2010). According to Article 7 of the Treaty to achieve these goals, special protective measures should be planned and developed in Antarctica to avoid anthropogenic environmental impact, including through the prohibition of any activity on the industrial development of mineral resources. An exception is provided for scientific research (Goldsworthy and Hemmings 2008). In addition, international legal regulation of the Antarctic mineral resources regime was supposed to be governed by the Convention on the Regulation of Mineral Resources of Antarctica (1988). The main idea and purpose of the Convention is that the development of resources should not cause any harm to the natural environment. It is controlled by the establishment of conditions and procedures for the development and production of mineral resources. Nevertheless, there is a problematic issue regarding the use of these resources. Most likely, some industrialized countries with territorial claims in Antarctica without their own resources will expand the scope of research work to uncover the prospects of using the region's mineral resources (Lagoni 1979; Brazovskaya and Ruchkina 2020). This may become a real threat to these resources and contribute to their further degradation.

The biggest problem for polar ecosystems is global climate change (Turner et al. 2013; Ciechanowicz-McLean 2017), caused by the accumulation of greenhouse gases in the troposphere, i.e. carbon dioxide and methane, which contribute to climate warming. All the more so as greenhouse gas emissions are likely to be evident at a variety of scales, both temporally and spatially (Parry et al. 2007). Furthermore, in the Antarctic, changes in stratospheric ozone are now also thought to have contributed to observed climate change effects (Thompson and Solomon 2002), with the interaction effects of ozone and CO₂ increasingly recognized as important (Mayewski et al. 2009; Turner et al. 2013). A consequence of this phenomenon is an increase in temperature, which causes gradual melting of glaciers and other climatic anomalies (Convey and Smith 2006; Bosello et al. 2007; Szafraniec 2018; Lowry et al. 2019; Świątecki et al. 2019). Temperature variation studies over 50 years (1971–2000) showed an increasing trend at a rate of 0.56°C per decade over the year and 1.09°C per decade during the winter (Turner et al. 2005). Another study confirmed that the Antarctic ice sheet is losing 152 km² of ice per year as a consequence of a 2°C increase in temperature (Serreze et al. 2007). Climate changes contribute to changes in environmental conditions, especially water temperature and trophy (Castini et al. 2008; Trathan and Agnew 2010), which are visible in the species structure—the disappearance of cold-loving (sub-Arctic) species, which are becoming endangered species in favor of those commonly occurring in the temperate zone. Cyanobacteria have been able to adapt to climate changes as well as anthropogenic disturbances. These organisms exhibit the widest range of diversity of growth habitats and have developed CO₂ concentration mechanisms that adapt them to various environmental constraints (Chaurasia 2015). These rich natural resources are subjected to degradation due to global warming and pollution, thus, Antarctic regions are becoming the subject of scientific research by climatologists and biologists. The Antarctic Peninsula has some of the highest footprint values, in particular the ice-free areas where many stations and tourist attractions are concentrated, in particular King George Island with over 90 footprints on an area of approx. 4.5 km². The footprint maps show intense human activity in the area, which is associated with the exploration and pollution of the polar environment. It is therefore necessary to establish monitoring the programs for anthropogenic activities, environmental damage and non-native species (Pertierra et al. 2017). An example of the research institution is Arctowski Polish Antarctic Station at the King George Island.

The climate-related changes may affect the environmental conditions of water bodies especially lead to a higher trophy (Castini et al. 2008). In this study, the lowest average water temperature was noted in streams than in small water bodies in Antarctic summer (March/April) 2019. This fact is due to the outflow of water from the glacier feeding the water in the streams. High values of electrolytic conductivity (max. above 1000 µS cm⁻¹) and nutrient concentration (TP, TN, N-NH₄ and P-PO₄) in studied streams and small water bodies were also recorded. Moreover, the five-time higher TP and PO₄ values were in the streams than small water bodies. It all confirms that Antarctic environment were characterized by the high nutrient concentrations. Namely, some authors recorded similar nutrient concentrations (3 mg L⁻¹ TN and 4 mg L⁻¹ TP) near snow fields, snow-fed streams of small to intermediate size and glacial rivulets running continuously during the summer season in this region. The snow-fed streams are the most common and diverse freshwater ecosystems (Elster and Komarek 2003). However, their nutrient content, and therefore water trophic status, could be increased from external nutrient sources like bird colonies as e.g. penguins or by increased weathering of rocks (Vincent and Laybourn-Parry 2008; Kviderova and Elster 2013).

The cause of high nutrient content is eutrophication, even in Antarctic water ecosystems. The high trophy of water reservoirs is a factor favoring the growth of periphyton organisms (Rosemond 1993; Smith et al. 1999; Hillebrand 2002). In this study, it was indicated by the higher wet and dry weight of the stream mats at higher water trophy in comparison to the small water body mats. In addition, the higher variability of these values in the streams may be related to the greater dynamics of these waters caused by the inflow of water from the glacier. Similarly, the three-time higher total biomass of cyanobacteria and periphytic algae on microbial mats was found in the streams at high N and P contents than in the small water bodies.

Environmental conditions shape the structure and species composition of periphytic algae. In this study, the structure and species composition of the cyanobacteria and algal biomass was differentiated among the studied small water bodies and streams. Cyanobacteria, Bacillariophyta and Chlorophyta are the main representatives of periphytic assemblages inhabiting the microbial mats. The higher biomass dominance of Cyanobacteria was found in streams at six sites (max. above 90% of the total biomass) while this group dominated only at one site in the small water bodies (max. 57%). Diatoms reached the highest proportion in total biomass in the small water bodies (above 90%), whereas green algae in streams (up to 70–80%) with one exception with a high proportion of 66% at one site in the small water bodies. The domination of these three groups in the periphyton assemblages was also recorded by the other authors (Vinocur and Pizarro 1995, 2000). We suggest, that the recorded higher dominance of cyanobacteria in streams may be related to the higher water trophy. Similarly, Makhalanyane et al. (2015) also recorded the presence of cyanobacteria at extreme polar conditions, particularly with a high nitrogen concentration. Cyanobacteria were mainly represented by filamentous Planktothix agardhii (V class) accompanied by Planktolyngbya limnetica, Pseudanabaena catenata, Oscillatoria sancta and Microcoleus autumnalis with the proportion not exceeding 20% of the total biomass. Among diatoms, the most abundant was Fragilaria capucina especially on the small water body mats with maximum almost 80%. Other dominants were Planothidium lanceolatum, Achnanthidium pyrenaicum, Tabularia tabulata, Pinnularia microstauron, Gomphonella olivacea, Hantzschia abundans and Nitzschia commutata. Some authors also identified similar periphyton taxa (of the genera Fragilaria, Navicula, Tabellaria, Nitzschia) which colonized the artificial substrates in this Antarctic region (Segovia-Rivera and Valdivia 2016) and natural ones in subarctic lake (Maltais and Warwick 1997). P. borealis and F. capucina was also noted in the island King George Island (Vinocur and Pizarro 2000). In this study, chlorophytes were represented by Prasiola crispa (V class) at stream and Keratococcus mucicola (IV class) at small water body. Similar to this study, other researches was found Prasiola crispa in microbial mats (Vinocur and Pizarro 1995, 2000; Ferreira da Silva et al. 2019). This species often occurred in the places of the inflow of water from the vicinity of penguins. P. crispa is considered to be ornithocoprophilic, it presents a significant biomass mainly around penguin colonies, where the availability of nutrients for both green algae and the surrounding diatoms is higher compared to other habitats (Putzke and Pereira 2001). Moreover, this species is a natural substrate for smaller algae, e.g. diatoms. Thus, it constitutes a unique environment for the periphytic algae of small Antarctic water bodies. We suggest that a large share of periphytic species commonly occurring, e.g. Planktothix agardhii, Planktolyngbya limnetica, Fragilaria capucina and Gomphonella olivacea, and limiting the typically polar ones, may indicate the progressive changes in the eutrophication of Antarctic waters.

Generally, the lowest biodiversity were noted on mats in the region of moraine stream of the Ecology Glacier, whereas the highest on mats in the Petrified Forest Stream. The majority of dominant species inhabiting the Antarctic mats are recognized as commonly found worldwide also in freshwater phytoplankton. Referring these species to functional patterns, it was found that they can be the representatives of at least five functional coda S1, T_B, MP, D and P (Reynolds et al. 2002; Padisák et al. 2009). Planktothix agardhii and Planktolyngbya limnetica are typical of turbid mixed environments and known as shade-adapted cyanobacteria (codon S1). Thus, their mass occurrence was primarily confirmed for side moraine stream of the Ecology Glacier. The various taxa of the genera Achnanthidium, Planothidium, Gomphonella, Navicula are representatives of codon T_B and usually occur in highly lotic environments (streams and rivulets). Cyanobacteria Oscillatoria sancta and Pseudanabaena catenata are representatives of codon MP and typical of frequently stirred up, inorganically turbid shallow small water bodies. Tabularia tabulata and species of the genus Nitzschia are often noted in shallow turbid waters including rivers (codon D). Diatom Fragilaria capucina represents codon P with habitat template of continuous or semi-continuous mixed layer of 2–3 m in thickness at higher trophic states and its mass occurrence was highly related to small water body environment in Ornithologists reservoir system. The cluster analysis of taxonomic structure of periphytic assemblages indicated also a high similarity of sites situated in these small water bodies and streams on the slope of Upłaz moraine. Completely differently were grouped mats from sites of side moraine stream of the Ecology Glacier, area with penguin colony and some sites from Petrified Forest Stream and one in Czech creek with cyanobacteria Planktothix agardhii and Planktolyngbya limnetica as dominants. And lastly, similarly-connected mats primarily with a high biomass of chlorophytes Prasiola crispa and Keratococcus mucicola, and diatom Tabullaria tabulata came from rest of the studied sites (including Petrified Forest Stream, Czech creek, penguin area and inflow to the drinking water reservoir).

The important factors determining the growth of periphytic assemblages were water temperature and the availability of nutrients in the water. In the case of cyanobacteria, the main ecological factors influencing their growth is water temperature over 0°C in Antarctica (Komárek 2013). Cyanobacteria dominated at the average temperature of 2.4°C in King George Island (Vinocur and Pizarro 2000). An increase in the rate of cyanobacteria photosynthesis at increasing temperature in icy habitats was also observed (Fritsen and Priscu 1998). Moreover, periphytic algae are more sensitive to UV stress at low water temperature in ice streams. Generally, low temperatures slow down the growth rate of algae. However, it was observed a marked increase in the periphytic algae biomass at low turbidity and the lack of ice cover in the spring season (Uehlinger et al. 2009). Some authors recorded correlation between periphytic species and nutrient concentrations, indicating the uptake N and P by algae (Francoeur et al. 1999; Steinman et al. 1995; Dodds and Welch 2000; Mulholland and Webster 2010). In this study, the CCA analysis shows that the water temperature favors the growth of F. capucina and G. olivacea while nutrient concentrations stimulate A. pyrenaicum and P. crispa. Moreover negative relationships between the whole group Chlorophyta, dominating species K. mucicola and, H. abundans, T. tabulata, P. lanceolatum, N. commutata and nutrients suggest the phenomenon of uptake these elements from the water. This tendency was confirmed by statistically significant correlation between some cyanobacteria and algal biomass, and water temperature and nutrient concentrations. A. pyrenaicum was positively correlated with TN. Moreover P. agardhii was negatively correlated with water temperature. This species reached the highest biomass in streams at the lowest mean water temperature. However, the negatively correlation between K. mucicola and N-NH₄, G. olivacea, N. cryptocephala, P. obscura and P-PO₄, and G. olivacea, P. divergens, P. obscura and TP indicated the uptake of these elements from the water.

In summary, Antarctic environments have unique characteristics with different abiotic factors and specific substrates, creating the habitats for the periphytic organisms in small water reservoirs (small water bodies, streams), which often are formed as a result of melting glaciers. The significantly diversified periphytic assemblages between the microbial mats of small water bodies and streams indicated a great variability of environmental conditions, especially in streams. The structure of periphytic assemblages was mainly determined by the type of substrate and the physicochemical parameters of the water. Our results suggest the phenomenon of nutrient uptake by periphytic cyanobacteria and algae from the waters, confirmed by the negative correlations between some species and nutrients (TN, TP, N-NH₄, P-PO₄). We also suggest that a large share of periphytic species commonly occurring and limitation of typically polar ones, indicate progressive changes in the eutrophication of Antarctic waters caused by the global climate change and increase in the environmental pollution. Due to the global changes in the environment, these areas should be subjected to a special protection, preceded by detailed research, and should be left over by areas not under the jurisdiction of any country, because only this way it will be possible to preserve such a unique and valuable ecosystem for future generations.