Ecotonic Communities of Diatoms in the Southeastern Part of the Kamchatka Peninsula

: Data about the ecotonic diatom communities of the Kamchatka Peninsula, a unique territory with strong volcanic activity, are very limited. We aimed to investigate diatom algae of the ecotones in the southeastern part of Kamchatka, including the Paratunka river valley, at the foot of the Vachkazhets volcano, and the bank of the Bystraya river. In total, 55 taxa were identiﬁed. The most diverse were the ﬂora of the Paratunka river, with 31 taxa. Near the Bystraya river, 26 taxa were identiﬁed. Near the Vachkazhets volcano, 18 taxa were identiﬁed. Fragilariforma virescens , Planothidium lanceolatum , Pinnularia cf. subcapitata , Halamphora normanii , Nitzschia palea , and Eunotia exigua were the dominant species in the studied ecosystems, with the maximum abundance score. Pinnularia cf. subcapitata and Planothidium lanceolatum were found in all ecotones. In the studied habitats, small indifferent alkaliphilic cosmopolitan species prevailed. Our study revealed that the diatom species composition of the Kamchatka ecotones reﬂects their adaptability to survive in the extreme conditions of volcanic substrates. The results contribute to our knowledge of the ecology and biogeography of a number of diatom taxa.


Introduction
The Kamchatka Peninsula is a unique region that is characterized by a number of features. The first is the specificity of soils due to the following combination of a number of factors of soil formation: the cold, excessively humid climate in the coastal areas; the variety of relief; the vegetation features; and the special soil-forming rocks of volcanic origin [1][2][3][4][5][6][7]. The composition of the soil-forming rocks of Kamchatka includes volcanogenic deposits. There are three zones of ashfall influence on the peninsula. The central Kamchatka depression is located in the zone of moderate ashfall. The southern half of the West Kamchatka Lowland is located in the zone of moderate ashfall, a subzone of weakened ashfall. The northern half of the West Kamchatka Lowland is in the zone of weak ashfall [6]. In the first two zones, volcanic deposits are represented by volcanic sands and ash; in the third zone, volcanic deposits are represented by volcanic dust [8].
The second peculiarity is the climate. The great originality of the climate of the region is associated with its physical and geographical location. The difficult terrain leads to climate differences, even between closely located areas. The peninsula is dominated by strong winds, hurricanes, and storms and produces a significant amount of precipitation, depending on the large extent of the peninsula from north to south, the terrain, the proximity of large water spaces and the movements of cyclones [8,9]. There is frequent variability in the weather in all seasons of the year, especially in winter. In the central regions of Kamchatka, some winter months can be almost 10 • C colder or warmer than usual. On the

Studied Area
The environmental conditions of the territory of the Kamchatka Peninsula are characterized by a high level of heterogeneity, which was taken into account during the research. We analyzed the following three sites: the valley of the Paratunka river near the village of Paratunka; the foot of the Vachkazhets volcano near the village of Malki; and the bank of the Bystraya river in the village of Malki (Figure 1). the data concerning the diatoms of the ecotonic assemblage, including the diatoms of the coastal zone, are very limited and need further investigation.
The aim of this work was to study the biodiversity of the diatoms of some ecotones in the coastal zones of the southeastern part of the Kamchatka Peninsula.

Studied Area
The environmental conditions of the territory of the Kamchatka Peninsula are characterized by a high level of heterogeneity, which was taken into account during the research. We analyzed the following three sites: the valley of the Paratunka river near the village of Paratunka; the foot of the Vachkazhets volcano near the village of Malki; and the bank of the Bystraya river in the village of Malki (Figure 1). Figure 1. Study area. The red circle indicates Petropavlovsk-Kamchatsky. Sites P1-P4, V1-V2, and M1-M2 are numbered according to Table 1. According to the soil zoning of Kamchatka [7,38], the studied region belongs to the southeastern soil province. The surface organogenic horizon within the province was formed on the andesite-basalt gray coarse-grained ash of the 1907 eruption of the Ksudach volcano. All ash horizons, except the near-surface layer, have a predominantly acidic composition. The soil pH is acidic or slightly acidic.
Paratunka village geographically belongs to the Yelizovsky district of the Kamchatka Territory. It is located along the upper reaches of the Paratunka river, 25 km southwest of the city of Petropavlovsk-Kamchatsky. A river of the same name flows through the village, originating in the foothills of the Vilyuchinskaya Sopka volcano [39].
The Vachkazhets mountain range is located in the south of the Kamchatka Peninsula, the highest point of which is Mount Vachkazhets, with a height of 1556 m above sea level, which is located 80 km west of Petropavlovsk-Kamchatsky. Vachkazhets is an ancient volcano that was divided into three main parts as a result of a strong eruption [40].
Village Malki is situated on the Bystraya river, which flows along the southern part of the median ridge. Its length is 180 km, its depth ranges from 1 to 3 m, its width in the lower reaches is 50-100 m, and its width in the middle reaches is 20-40 m [41].

Sample Collection and Data Analysis
Eight soil samples were collected in August 2009 according to previously described methods [35,42] from the Paratunka river valley (four samples), the foot of the Vachkazhets volcano (two samples), and the bank of the Bystrica River (two samples). Small amounts of wet soil (50-100 g) from several random points at each studied site were taken with a metal cylinder and put into plastic bags. Thus, the sample from each site was a composite sample. In the laboratory, the samples were dried in the shade [43]. Thus, the diatom communities were studied along transects crossing the interface between the aquatic and terrestrial environments. In the laboratory, the samples were investigated using the standard procedure to study soil diatoms [43]. The samples were rinsed in deionized water and nitric acid, boiled in nitric acid, and washed in deionized water again. The diatoms were mounted on permanent slides in Naphrax [35].
For the estimation of the floristic similarities between ecotones, the Sørensen-Czekanowski coefficient was used, as follows: where K is the coefficient of the floristic similarity, c is the number of species common to the two floras, a is the number of species in the flora of the first area, and b is the number of species in the flora of the second area [54]. For a demonstration of the similarities between the diatom communities from the ecotones near the Paratunka river, the Vachkazhets volcano, and the Bystraya river, a Venn diagram was used [55,56]. It was created online using the web-based tool InteractiVenn [57] and edited manually using Microsoft Visio 2019.
The species abundance was calculated on a coverslip according to previously described methods [35,58]. The abundance of diatoms was estimated on a 15-point scale on a slide, where the minimum abundance corresponded to 1 point and the maximum abundance was 15 points.
A map of the study area was created using the online tool Google Earth [59].
The diatom communities of ecotones in the Paratunka river valley were the most diverse and accounted for 31 taxa (Table 2 and Figure 3). In the ecotones near the Bystraya river, 26 taxa were detected. In the ecotones near the Vachkazhets volcano, 18 taxa were detected (Table 2 and Figure 3). In sample P1 from the central part of the Paratunka river valley, 31 species were identified. This was the highest number of species in a sample. The lowest number of taxa (14) was found in sample V1, which was collected 3 km from the Vachkajec volcano (Table 2). An average of 6.9 species were identified in the samples. Five species (Encyonema silesiacum, Navicula cincta, Pinnularia cf. subcapitata, Planothidium lanceolatum ( Figure 2H), and Synedra ulna) were found in all of the studied ecotones ( Figure 3). This indicated the low level of similarity between the studied diatom communities. The similarities between ecotones obtained with a pairwise comparison were also low ( Figure  3); only 3-4 common species were detected. The diatom communities of the Paratunka river valley and the territory near the Vachkazhets volcano were the most similar ( Figure  3). The value of the Czekanowski-Sørensen coefficient was 16.3%. The similarity between the Paratunka river valley and the bank of the Bystraya river was 14.1%, and the similarity between the territory near the Vachkazhets volcano and the Bystraya river was 13.6%.
Fragilariforma virescens was a dominant species in the diatom communities in the Malki and Upper Paratunka hot springs [23]. Planothidium lanceolatum also dominated in The genera Gomphonema and Pinnularia (six species each); Eunotia (five species); and Encyonema, Navicula, and Sellaphora (three species each) had the largest numbers of species (Table 2).
The diatom communities of ecotones in the Paratunka river valley were the most diverse and accounted for 31 taxa (Table 2 and Figure 3). In the ecotones near the Bystraya river, 26 taxa were detected. In the ecotones near the Vachkazhets volcano, 18 taxa were detected (Table 2 and Figure 3). In sample P1 from the central part of the Paratunka river valley, 31 species were identified. This was the highest number of species in a sample. The lowest number of taxa (14) was found in sample V1, which was collected 3 km from the Vachkajec volcano (Table 2). An average of 6.9 species were identified in the samples. Five species (Encyonema silesiacum, Navicula cincta, Pinnularia cf. subcapitata, Planothidium lanceolatum ( Figure 2H), and Synedra ulna) were found in all of the studied ecotones ( Figure 3). This indicated the low level of similarity between the studied diatom communities. The similarities between ecotones obtained with a pairwise comparison were also low ( Figure 3); only 3-4 common species were detected. The diatom communities of the Paratunka river valley and the territory near the Vachkazhets volcano were the most similar ( Figure 3). The value of the Czekanowski-Sørensen coefficient was 16.3%. The similarity between the Paratunka river valley and the bank of the Bystraya river was 14.1%, and the similarity between the territory near the Vachkazhets volcano and the Bystraya river was 13.6%.
Fragilariforma virescens was a dominant species in the diatom communities in the Malki and Upper Paratunka hot springs [23]. Planothidium lanceolatum also dominated in the Kamchatcan hot springs [23]. Fragilariforma virescens and Planothidium lanceolatum were dominant species in the ecotones of the Paratunka river valley and the Vachkazhets volcano (Table 2 and Figure 3). Planothidium lanceolatum was also detected in the samples from the Bystraya river bank ( Table 2). Pinnularia cf. subcapitata prevailed in several samples from all of the studied ecotones (Table 2 and Figure 3). Halamphora normanii and Nitzschia palea dominated in the ecotones in the Paratunka river valley ( Table 2). Eunotia exigua dominated in the communities of the Bystraya river bank ( Table 2).
Earth 2023, 4, FOR PEER REVIEW 6 the Kamchatcan hot springs [23]. Fragilariforma virescens and Planothidium lanceolatum were dominant species in the ecotones of the Paratunka river valley and the Vachkazhets volcano (Table 2 and Figure 3). Planothidium lanceolatum was also detected in the samples from the Bystraya river bank (Table 2). Pinnularia cf. subcapitata prevailed in several samples from all of the studied ecotones (Table 2 and Figure 3). Halamphora normanii and Nitzschia palea dominated in the ecotones in the Paratunka river valley (Table 2). Eunotia exigua dominated in the communities of the Bystraya river bank (Table 2).      Our study revealed the existence of a wide range of ecological groups in the studied ecotonic communities of diatoms. They belonged to benthic, littoral, planktonic, epiphyticlittoral, littoral-planktonic, benthic-planktonic, epiphytic-planktonic, benthic-epiphytic, and epiphytic algae ( Table 2). Typical benthic (18 taxa, 33%) and epiphytic (11 taxa, 20%) diatoms were the most diverse groups. Epiphytic-littoral algae accounted for 10 species. The benthic-epiphytic group was represented by nine taxa. The remaining groups were individually represented (1-2 species).

Discussion
In the studied diatom communities, a characteristic feature was the predominance of cold-loving species that are common in temperate zones, which had adapted to living in the conditions of highly mineralized substrates. The predominance of cold-loving species of diatoms is probably explained by the specifics of the studied ecotones. It has been established that plain shrub tundras are often located within the territories of the valleys of large rivers, in floodplains, and on upper floodplain terraces. These communities are situated in the floodplain of the lower reaches of the Bystraya river [13].
As noted above, the dominant complex of the diatoms of the studied territories was represented by the following five species: Fragilariforma virescens, Halamphora normanii, Nitzschia palea, Pinnularia cf. subcapitata, and Planothidium lanceolatum. Encionema silesiacum, Navicula cincta, Pinnularia cf. subcapitata, Planothidium lanceolatum, and Synedra ulna were common to all three habitat groups. These taxa are abundant in both soil substrates and aquatic ecosystems [33,34,60], which corresponds to the formation of the species diversity of ecotonic communities.
Species diversity is the result of the formation of sustainable ecosystems. In stable habitat conditions, more species can exist. On volcanoes, the substrates are not formed and are loose, which negatively affects biodiversity. Therefore, in soil samples near the Vachkazhets volcano, less species were found than near the Paratunka and Bystraya rivers. The climate of the southern volcanic district of Kamchatka, near which the ecotonic communities of the Paratunka river are located, is characterized by intense cyclonic activity and a high level of precipitation [13], which probably affects the rich species diversity of diatoms.
According to the results of previous studies of diatom algae of the Kamchatka Peninsula [35], the species composition of the studied ecosystems was similar to the diatom complexes of the Malki, Upper Paratunka, and Dachnie thermal springs. In both ecotonic communities and in soils near hot springs, representatives of the genera Encyonema, Navicula, and Pinnularia prevailed. A number of local "spots of life", associated with the edge effect, could be distinguished. These "spots" include, among other things, the ecosystems of hot springs, lakes, and floodplains of rivers that are periodically flooded. Previous studies have shown that life in aquatic systems is concentrated and most active in the water layers adjacent to the external and internal sections with active surfaces [61].
It should be noted that the communities of diatoms in ecotones near water significantly differed from similar communities of previously studied soils of the Mutnovsky and Gorely volcanoes [37]. These differences were especially pronounced in the composition of the diatoms. In contrast to the studied ecotonic communities of Kamchatka diatoms, the soils of Mutnovsky and Gorely were dominated by Pinnularia borealis and Humidophila contenta, which are often detected in terrestrial habitats [62,63]. Caloneis bacillum and Encyonema sudetica, which were absent in the well-moistened substrates of ecotones, were found in volcanic soils.
The similarity of the diatom communities of the soils of the Mutnovsky and Gorely volcanoes and the studied ecotones consisted of the frequent occurrence of various representatives of the genus Pinnularia.
Pinnularia cf. subcapitata and Planothidium lanceolatum were found in all studied habitats, including ecotones in the Paratunka river valley, near the Vachkazhets volcano, and near the Bystraya river; in the soils near the Malki, Upper Paratunka and Dachnie thermal springs [35]; and in the soils of the Mutnovsky and Gorely volcanoes [37]. These taxa are widely distributed in different ecosystems around the world [49,60,64,65]. These data once again confirmed that in the terrestrial ecosystems of Kamchatka, the main part of the diatom algae community is represented by small cosmopolitan benthic forms. The same results were obtained in previous studies [35,37].
Most of the identified taxa belong to species that are recognized as freshwater species. This does not fully reflect their ecological characteristics. For example, at least some taxa, such as Fragilariforma virescens, Eunotia exigua, Planothidium lanceolatum, and Nitzschia palea, should be considered not only freshwater but also terrestrial species.
Thus, our studies of the communities of diatoms of the Kamchatka Peninsula have shown that the species composition of these communities reflects their adaptability to living in the conditions of organically poor volcanic substrates with sharp pH fluctuations, high concentrations of some elements, and a cold climate. In such conditions, the selection of the most resistant species with high adaptability to extreme environmental conditions is underway. The results of this research allow us to expand our knowledge about the ecology and biogeography of a number of diatom genera and species and will contribute to the more intensive study of these organisms in volcanic habitats around the world.