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Broad-scale assessment of biodiversity is needed for detection of future changes across substantial regions of the Arctic. Presently, there are large data and information gaps in species composition and richness of the freshwater planktonic and meiobenthos communities of the Russian Arctic. Analysis of these data is very important for identifying the spatial distribution and temporal changes in species richness and diversity of rotifers, cladocerans, and copepods in the continental Russian Arctic. We investigated biogeographic patterns of freshwater plankton and meiobenthos fromc. 67 degrees to 73 degrees N by analysing data over the period 1960-2017. These data include information on the composition of rotifers, cladocerans, and copepods obtained from planktonic and meiobenthic samples, as well as from subfossil remains in bottom sediments of seven regions from the Kola Peninsula in the west, to the Indigirka River Basin (east Siberia) in the east. Total richness included 175 species comprised of 49 rotifer genera, 81 species from 40 cladoceran genera, and 101 species from 42 genera of calanoid, cyclopoid, and harpacticoid copepods. Longitudinal trends in rotifer and micro-crustacean diversity were revealed by change in species composition from Europe to eastern Siberia. The most common and widespread species were 19 ubiquitous taxa that includedKellicottia longispina(Rotifera),Chydorus sphaericuss. lat. (Cladocera),Heterocope borealis,Acanthocyclops vernalis, andMoraria duthiei(Copepoda). The highest number of rare species was recorded in the well-studied region of the Bolshezemelskaya tundra and in the Putorana Plateau. The total number of copepod and rotifer species in both Arctic lakes and ponds tended to increase with latitude. Relative species richness of copepods was positively associated with waterbody area, elevation, and precipitation, while relative species richness of cladocerans was positively related to temperature. This result is consistent with known thermophilic characteristics of cladocerans and the cold tolerance properties of copepods, with the former being dominant in shallow, warmer waterbodies of some western regions, and the latter being dominant in large cold lakes and waterbodies of eastern regions. Rotifers showed a negative association with these factors. Alpha- and beta-diversity of zooplankton in the Russian Arctic were strongly related to waterbody type. Lake zooplankton communities were more diverse than those in pond and pool systems. Moreover, the highest beta-diversity values were observed in regions that showed a greater breadth in latitude and highly heterogeneous environmental conditions and waterbody types (Bolshezemelskaya tundra and Putorana Plateau). Redistribution of freshwater micro-fauna caused by human activities occurred in the 1990s and 2000s. As a result of climate warming, a few cladoceran species appear to have extended their range northward. Nevertheless, the rotifer and micro-crustacean fauna composition and diversity of the majority of Arctic regions generally remain temporally conservative, and spatial differences in composition and species richness are chiefly associated with the differences between the warmer European and colder east Siberian climates.

We studied the morphology of Eurytemora from inland waters at the shores of the White and Pechora seas and from the Lena River delta, and revealed a ubiquitous presence of Eurytemora gracilicauda Akatova, which results we confirmed with genetic data. We found this species for the first time in the Pechora Sea basin. In the White Sea basin, this species was previously described as E. brodskyi Kos, with the name that we suggest is a junior synonym of E. gracilicauda. E. gracilicauda differs from the co-living species: E. lacustris (Poppe), E. arctica Wilson M. S. & Tash, and E. raboti Richard, by the structure and armament of the caudal rami and the fifth legs (P5) of males and females. The caudal rami of both males and females were elongated. The female caudal rami showed a surface covered by spines. The male caudal rami were bare, or with rare spines on the sides. The appendages of the female P5 were also elongated: the length of the inner spine on the distal exopod segment was 2.27 ± 0.12 times as long as the outer spine; the exopod of the male right P5 had a specific trigonal ledge with a short spinule, and the coxopods (both or at least one) had groups of spinules. The morphometric parameters of the females were quite stable, while those of the male showed high variability within and between populations (CV = 11.5-43.5%). Similarities and differences of E. gracilicauda and three allochoric Eurytemora species were analysed, and the results presented herein.

A harpacticoid copepod (Copepoda: Harpacticoida) species, Elaphoidella bidens, which was new for the North-East of European Russia, was found in the Vychegda River in July 2018. The species was identified in the area where heated wastewater is discharged from the wood-processing plant. The species was found in the extreme north of its range (61°48′ N). The present study compares the morphological, biological and ecological properties of this species with those of another native representative of the genus – E. gracilis. Comparison of morphology of the Vychegda E. bidens and individuals from tropical populations (New Zealand, Borneo, Vietnam) and populations of the temperate zone (Romania, Lake Glubokoe in Moscow region) showed that the structures of their antennae, body somites, swimming and rudimentary legs, and the caudal rami were similar in representatives of all populations. The fact that a thermophilic species was found for the first time in the northern region is indicative of potential changes in fauna diversity caused by thermal pollution or warming

Climate warming and subsequent landscape transformations result in rapid ecological change in Arctic freshwaters. Here we provide a synthesis of the diversity of benthic diatoms, plankton, macrophytes, macroinvertebrates, and fish in Arctic freshwaters. We developed a multi-organism measure of α diversity to characterise circumpolar spatial patterns and their environmental correlates, and we assessed ecoregion-level β diversity for all organism groups across the Arctic. Alpha diversity was lowest at high latitudes and elevations and where dispersal barriers exist. Diversity was positively related to temperature, and both temperature and connectivity limited diversity on high latitude islands. Beta diversity was highly variable among ecoregions for most organism groups, ranging from 0 (complete similarity) to 1 (complete dissimilarity). The high degree of dissimilarity within many ecoregions illustrates the uniqueness of many Arctic freshwater communities. Northward range expansion of freshwater taxa into Arctic regions may lead to increased competition for cold-stenothermic and cold-adapted species, and ultimately lead to the extinction of unique Arctic species. Societal responses to predicted impacts include: (1) actions to improve detection of changes (e.g., harmonised monitoring, remote sensing) and engagement with Arctic residents and Indigenous Peoples; and (2) actions to reduce the impact of unwanted changes (e.g., reductions of CO2 emissions, action against the spread of invasive species). Current Arctic freshwater monitoring shows large gaps in spatial coverage, while time series data are scarce. Arctic countries should develop an intensified, long-term monitoring programme with routine reporting. Such an approach will allow detection of long-term changes in water quality, biodiversity, and ecosystem services of Arctic freshwaters.

1. Arctic freshwaters are facing multiple environmental pressures, including rapid climate change and increasing land-use activities. Freshwater plankton assemblages are expected to reflect the effects of these stressors through shifts in species distributions and changes to biodiversity. These changes may occur rapidly due to the short generation times and high dispersal capabilities of both phyto- and zooplankton. 2. Spatial patterns and contemporary trends in plankton diversity throughout the circumpolar region were assessed using data from more than 300 lakes in the U.S.A. (Alaska), Canada, Greenland, Iceland, the Faroe Islands, Norway, Sweden, Finland, and Russia. The main objectives of this study were: (1) to assess spatial patterns of plankton diversity focusing on pelagic communities; (2) to assess dominant component of β diversity (turnover or nestedness); (3) to identify which environmental factors best explain diversity; and (4) to provide recommendations for future monitoring and assessment of freshwater plankton communities across the Arctic region. 3. Phytoplankton and crustacean zooplankton diversity varied substantially across the Arctic and was positively related to summer air temperature. However, for zooplankton, the positive correlation between summer temperature and species numbers decreased with increasing latitude. Taxonomic richness was lower in the high Arctic compared to the sub- and low Arctic for zooplankton but this pattern was less clear for phytoplankton. Fennoscandia and inland regions of Russia represented hotspots for, respectively, phytoplankton and zooplankton diversity, hereas isolated regions had lower taxonomic richness. Ecoregions with high α diversity generally also had high β diversity, and turnover was the most important component of β diversity in all ecoregions. 4. For both phytoplankton and zooplankton, climatic variables were the most important environmental factors influencing diversity patterns, consistent with previous studies that examined shorter temperature gradients. However, barriers to dispersal may have also played a role in limiting diversity on islands. A better understanding of how diversity patterns are determined by colonisation history, environmental variables, and biotic interactions requires more monitoring data with locations dispersed evenly across the circumpolar Arctic. Furthermore, the importance of turnover in regional diversity patterns indicates that more extensive sampling is required to fully characterise the species pool of Arctic lakes. α diversity, β diversity, ecoregions, latitude, taxonomic richness, temperature

As a result of studying different populations of crustaceans of the genus Eurytemora Giesbrecht from the inland water bodies of the basins of the White Sea, the Pechora Sea, the Lena River delta, and Pacific coast of the United States, the species Eurytemora gracilicauda Akatova 1949 has been found along the entire northern border of the Russian Eurasia, while North American E. americana Williams 1906 has not been registered within these limits. Clear morphological and molecular genetic differences between E. gracilicauda and E. americana are presented.

The structure and diversity of zooplankton of the mouth of the largest river in the European North, the Pechora, is studied. The river delta, an adjacent piece of the Pechora course, the estuary (Korovinskaya Bay), and lakes on its northern coast—in Timan Tundra—are in the studied region. In the delta of the Pechora River, the planktonic fauna is rich and unique in structure, in which rotifers (105 species) and cladocerans (55 species) prevailed; thermophilic invertebrates are present in zooplankton, but psychrophilic ones are revealed. Among copepods, brackish taxa and also a possible recent invader of the region (Eurytemora sp.) are found. The analysis of alpha and beta diversities of planktonic communities of the studied region shows the highest indexes for the delta water bodies relative to others and for the lake zooplankton in general. In our opinion, such diversity is due to a variety of environmental conditions and also features of gradients of the dominating environmental factors: temperature, anthropogenic, etc.

The phylogenetic relationships of four dioecious populations and one parthenogenetic population of the harpacticoid Canthocamptus staphylinus (Jurine, 1820) were studied. Analysis of the mtCOI gene revealed two main clades as a phylogenetic tree and a network of haplotypes: a clade with Fennoscandian populations in Lake Paajarvi (Finland) and Lake Vanern (Sweden), and a second clade with populations in Lake Vortsjarv (Estonia), Orlov Pond in Saint Petersburg (Russia), and the type locality of the species in Lake Geneva (Switzerland). The parthenogenetic population of C. staphylinus showed the smallest nucleotide and haplotype polymorphisms and could have evolved as a reaction to the changing environmental conditions following the Last Glacial Maximum, 20K YBP.

One hundred and eight species and forms of planktonic organisms have been revealed in three small reservoirs in the Komi Republic (the northeast of European Russia). Species that were not previously known for the water bodies of the Vychegda River Basin (Limnosida frontosa) and the Republic of Komi (Lecane mira, Macrochaetus subquadratus, Filinia longiseta limnetica, and Rhynchotalona falcata) have been found. It has been established that the richness of the planktonic fauna depends on the age of the water body: the maximum number of species is found in the oldest reservoir, namely, the Kazhim Reservoir. The planktonic communities of artificial reservoirs are distinguished by a low level of similarity of faunas both with each other and in comparison with the natural lakes of the region. The fauna distribution in the old reservoirs is uneven. The relatively large fauna richness of planktonic communities in the littoral zones is due to the water-level regime in the reservoirs.

External morphological and genetic structures of 94 individuals of Canthocamptus staphylinus Jurine (Harpacticoida, Copepoda, Crustacea) from ten European water bodies differing in type, including species type locality, have been analyzed. Significant distinctions of populations on six morphological features and morphometric indexes are established. The variability of both morphological and genetic markers is noted. As a result, two main species morph forms are allocated, typical and small. According to nucleotide, the variety of mitochondrial DNA harpacticoid specimens falls into ten haplotypes and three clades on the phylogenetic tree. One of them corresponds with the group isolated on morphological features (harpacticoids from the Sysola River basin, Komi Republic). The same-sex population from Lake Paajarvi (Finland), which is morphologically indistinguishable from the population from a type locality, is considerably divergent by nucleotide sequences of mtDNA. The role of geographical isolation and ecological factors in C. staphylinus microevolution is shown.

SUMMARY 1. We studied the fatty acid (FA) composition of six species of Cladocera and six species of Cope-poda from five cold-water lakes, situated in the tundra and/or in the mountains, and eight speciesof Cladocera and four species of Copepoda from eight warm-water lakes (including one reservoir) intemperate regions.2. We asked whether the contrasting temperature would result primarily simply in changes in thepercentages (i.e. percentage of total FAs) and absolute contents (quantities) of the long-chain polyun-saturated fatty acids (PUFAs), eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), or whether there are other FAs with various number of double bonds and/or chain lengthswhich could be responsible for a putative homeoviscous adaptation. We also aimed to reveal anyconsistent phylogenetic differences in FA percentages and contents between Cladocera and Cope-poda, separable from any temperature effects.3. Both taxa in warm waters had greater percentages of 18:0, and lower percentages of 14:0 and18:4n-3, than in cold waters, but there were no differences in percentages of DHA. In addition,Cladocera, besides the lower percentage of EPA, had higher percentages of 20:0 and 22:0 in warmwaters. These patterns in the percentages of 14:0, 18:0, 18:4n-3, 20:0 and 22:0 are in a good agreementwith the hypothesis of homeoviscous adaptation. Thus, the role of EPA, and particularly DHA, asunique regulators of the homeoviscous adaptation of the zooplankton may have been overestimated.4. Overall, we confirmed the known differences between Cladocera and Copepoda, namely higherpercentages of EPA in Cladocera and higher percentages of DHA in Copepoda. However, there wasc. 50% overlap in the ranges of the percentage of EPA in Cladocera and Copepoda, while the rangesin the content of EPA per unit organic carbon in Cladocera and Copepoda overlapped completely.Differences in the percentages and content of DHA between Cladocera and Copepoda were statisti-cally significant and invariant with temperature, and therefore are probably due to phylogenetic fac-tors, rather than any temperature adaptation.5. Contrasting temperature was not associated with significant differences in the contents of EPAand DHA per unit of organic carbon within the taxa studied. If this remained the case in a warmingclimate, such warming would be unlikely to reduce the accumulation of these important PUFAs inthe zooplankton, at least if species composition was unchanged. However, if there were shifts in theproportions of Cladocera and Copepoda in the zooplankton, for example fewer copepods as temper-ature rises, a decrease of the flux of PUFA in the ecosystem is plausible, taking into account the phy-logenetic (and temperature invariant) differences in DHA between the two groups.Keywords: climate warming, essential polyunsaturated fatty acids, temperature adaptation, zooplankton

We have studied the fatty acid (FA) contents and composition of cladocerans and copepods from warm and cold lakes. We have found no significant differences in FA percent levels and per carbon contents of cladocerans from warm and cold lakes or of copepods from warm and cold lakes. A discriminant analysis showed that all cladocerans differed from all copepods mainly due to the content of docosahexaenoic acid. Compared to cladocerans, copepods had significantly higher levels of all C22 polyunsaturated FA. Thus, we conclude that cladocerans and copepods in all environments had comparatively invariant taxon-specific compositions and contents of long-chain highly unsaturated fatty acids (HUFAs). According to HUFA content, all studied copepods can be regarded as a valuable food for fish.

We studied the taxonomic composition and the ecological characteristics of freshwater copepods collected from two lakes and 41 water bodies of the European northeast tundra and from 39 lakes in the northern taiga of Central Siberia. Both regions are situated beyond the Arctic Circle (Russia). Up to seven planktonic and 13 benthic species were recorded in the European tundra lakes and 27 species occurred in the small tundra water bodies. The taiga lakes of the Siberian region harboured 31 species. We confirmed the exclusively European distribution of Bryocamptus zschokkei komi Borutzky and the restricted distribution of Leptodiaptomus angustilobus (Sars) and Neutrodiaptomus pachypoditus (Rylov) in Asian ponds. Overall, we found a higher diversity of calanoids in the Siberian taiga than in the European tundra region. In addition, our results show that the biomass of particular copepod species, but not the total copepod biomass, is related to the surface area of lakes, size of small water bodies, the ecologi...

In 11 lakes from cold and warm regions we studied the content of highly unsaturated fatty acids (HUFA) in seston (

Data of more than 30 years about the harpacticoid copepods of the North-East of European Russia were used to investigate planktonic and benthic species in different types of water bodies. All 28 species and subspecies of harpacticoids known for the study region were found in summer. In spring, Attheyella nordenskjoldi nordenskjoldi and Moraria brevipes reproduced in the rivers and Canthocamptus staphylinus staphylinus bred in temporary water bodies. In the investigated river, the harpacticoid abundance was controlled primarily by water level, while in lentic habitats water temperature determined the formation of egg-sacs in females. Temperature conditions also influenced the speed and duration of ontogenesis. Timing of reproduction of the widespread and dominant species varied depending on temperature conditions for each area of the region under study.

We studied micro-benthic copepods and cladocerans in the bottom substrates of 12 lakes in the Bol’shezemel’skaya tundra in North-East European Russia during the summer. About 30 species of Cladocera and 28 species and subspecies of Copepoda were found. The majority of the micro-crustaceans are palaearctic or northern palaearctic. But the harpacticoid fauna of the western part of the studied region had specific European features, and three species of the harpacticoid fauna in the eastern part of the region were Siberian. It is therefore a boundary territory for two zoogeographical regions, the arctic and subarctic zones. Acidophilic (Arcticocamptus arcticus (Lilljeborg 1902)) and halophilic (Microsetella norvegica (Boeck 1864)) harpacticoid species were found in the lakes of the eastern part of Bol’shezemel’skaya tundra. On basis of their way of locomotion we distinguished five ecological groups and on basis of their feeding habits four ecological groups of micro-crustaceans. Groups with a similar way of locomotion were likely distributed over the studied water bodies. Habitat (inshore versus offshore), substrate particle size and substrate hardness were of paramount importance for the species distribution.

To obtain a relevant information on copepod biodiversity/distribution in continental Borneo water bodies in June 2011 about 30 different sites in Malaysian state Sabah were visited and more than 50 alcohol and formalin preserved samples in nine rivers, 10 ponds, and six near-road ditches and canals, rice fields and forest leaf litter environment were collected. In literature 16 copepod species were referred for Borneo and 10 other species for Kalimantan (Indonesean) states. After the Sabah sample analyses, the copepodspecies richnessin the Borneo island increased more than twice. The most abundant with species number genera were ranged as: Mesocyclops (13), Elaphoidella (6), Microcyclops (5), Eucyclops (4), Thermocyclops (4), Halicyclops (3) and Paracyclops (3). Species biodiversity in different sites plotted against type of water body and several environment parameters revealed significant positive correlations for number of species and both for depth and temperature in sampling site (Pearson non-parametric tests 0.6 and 0.5 respectively at p < 0.05). One way Kruscal-Walise dispersal analysis confirmed significant relationship between copepod biodiversity and water transparence/ turbidity (p < 0.05). The highest copepod biodiversity values were found in ponds (23 species), near road ditches (15), rivers with transparent water (12), lowland or swamp areas related with rivers (9). The lowest number of species were found in rivers with turbid water colored in orange with soil-erosive matter where the average number of copepod species (0.2 ± 0.08 species per site) was about 20 times less than in waters without silt particles (3.8 ± 2.8 species per site). This indicates a strong negative effect of soil erosion resulting water land-used activities and deforestation in the watershed on the biodiversity of aquatic organisms in Borneo. In one sub-urban population of Mesocyclops cf. thermocyclopoides, a trans-sexual mutation of female-sized but constructed as male armed with genicu late antennule organisms was found that possibly reflect a negative result of wide artificial hormone-based pesticide usage in this area. Keys for Harpacticoida species for Borneo and for Eucyclops species known for SEAsia, Australia and India are provided. Within practically each copepod genus studied in Borneo there are forms with problems on species identification by existing faunistic keys. This possibly indicates a necessity of new species description from this area in the nearest future.

For the first time a faunistic and ecological review of 18 harpacticoid species and forms from Estonia is presented. They were sampled in May and September and inhabit different types of freshwater habitats: from micro-waterbodies among hygrophilous plants to large lakes of Peipsi and Vortsjarv. The harpacticoid species occurring in Estonia belong to thermophilic, cold- preferring, and eurythermic ecological groups. A new harpacticoid subspecies Maraenobiotus brucei estonicus E. Fefilova subsp. nov. from wet plants under a waterfall is described. It differs from the known subspecies of M. brucei in the structures of the exopodite of antenna, mandibular palp, endopodite of leg 2, and spines on abdominal somites.