Polar Science 27 (2021) 100533

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Response of Arctic biodiversity and ecosystem to environmental changes:
Findings from the ArCS projectToru Hirawake a, *, Masaki Uchida b, c, Hiroto Abe a, Irene D. Alabia d, Tamotsu Hoshino e,
Shota Masumoto f, Akira S. Mori f, Jun Nishioka g, Bungo Nishizawa b, Atsushi Ooki a,
Akinori Takahashi b, c, Yukiko Tanabe b, c, Motoaki Tojo h, Masaharu Tsuji i, Hiromichi Ueno a,
Hisatomo Waga a, Yuuki Y. Watanabe b, c, Atsushi Yamaguchi a, Youhei Yamashita jaFaculty of Fisheries Sciences, Hokkaido University, Japan
National Institute of Polar Research, Japanc
The Graduate University for Advanced Studies, SOKENDAI, Japand
Arctic Research Center, Hokkaido University, Japane
Hachinohe Institute of Technology, Japanf
Yokohama National University, Japang
Institute of Low Temperature Science, Hokkaido University, JapanhOsaka Prefecture University, Japani
National Institute of Technology, Asahikawa College, Japanj
Faculty of Environmental Earth Science, Hokkaido University, Japanb

A R T I C L E I N F O

A B S T R A C T

Keywords:
Bering and Chukchi seas
Sea ice
Biodiversity
TundraLake

Arctic ecosystems are altered profoundly by climate changes. However, the responses of Arctic marine andterrestrial ecosystems as well as their biodiversity to global warming remain largely unknown. This article
provides comprehensive insights into the results and major findings from the Arctic Challenge for Sustainability(ArCS) Project – an Arctic region research program initiated in Japan, which aims to address and advance ourunderstanding of these uncertainties. Marine ecosystem studies have identified several biogeochemical processes
that are associated with sea ice decline and northward transport and shift of marine species across multiple
trophic levels over the Bering and Chukchi Sea shelves. Studies of the terrestrial ecosystem have identified factorsthat are important for the understanding of terrestrial biodiversity and ecosystems, including Arctic lakes, under
the presence of global warming. Novel fungal species from the Arctic terrestrial ecosystem have also been iso­lated and described. Overall, these results could contribute to the conservation and sustainable management of
the Arctic ecosystem services.

1. Introduction
Arctic surface air temperature has increased considerably in response
to global warming; the rate of temperature increase over the Arctic is 2.4
times the rate of increase over the northern hemisphere (Box et al.,2019) and 3 times that of the global average warming rate for the past
100 years (Overland et al., 2017; Steele et al., 2008). Abrupt reductionof Arctic sea ice (Comiso, 2006) is a clear impact of Arctic warming; therate of sea ice decline is higher than the rates that have been forecast by
numerical simulations and reported in the Intergovernmental Panel on
Climate Change Fourth Assessment Report (IPCC AR4) (Stroeve et al.,2007). These rapid climate changes and their concomitant effects aredefinitely impacting Arctic marine and terrestrial ecosystems, including
habitats, diversity, growth phenology, and other elements (AMAP,2019). In addition to climate-related stressors, human-induced
ecosystem impacts are also becoming a major concern in the region.
The Arctic marine ecosystem needs sea ice, which serves as a plat­form for marine life and plays a crucial role in controlling physical andchemical processes that affect biological activity. Therefore, sea ice
reduction, its timing, and accompanying ocean temperature increase
alter marine environments, inducing changes in primary production(Arrigo et al., 2008; Hirawake et al., 2012), benthic biomass and* Corresponding author. 3-1-1, Minato-cho, Hakodate, Hokkaido 041-8611, Japan.
E-mail address: hirawake@fish.hokudai.ac.jp (T. Hirawake).
https://doi.org/10.1016/j.polar.2020.100533
Received 11 January 2020; Received in revised form 5 May 2020; Accepted 13 May 2020
Available online 20 May 2020
1873-9652/© 2020 Elsevier B.V. and NIPR. All rights reserved.

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Polar Science 27 (2021) 100533

diversity (Grebmeier et al., 2006a, 2006b; Grebmeier, 2012), fishabundance (Stevenson and Lauth, 2012) and regional distributions ofplankton (Matsuno et al., 2011, 2014) and fishes (Fossheim et al., 2015).
Shifts in habitat of marine living resources are an important focus forscientific research but also raise concerns for global food security andsustainability of industrial fisheries in Arctic countries (Christiansen
et al., 2014). In addition, human impact such as bycatch (Davis et al.,2013) and contaminant accumulation in marine food webs (Wania andMackay, 1996) are posing increasing threats to the Arctic marine
ecosystem. Whereas uncertainties in the mechanisms and processes ofbiogeochemical cycles are being steadily addressed, our knowledge ofthe marine ecosystem and food web dynamics remains limited. Thus,
one of the impelling goals of international scientific community is toadvance our understanding of these uncertainties in the Arctic Ocean
and adjacent seas to ensure sustainability of marine biological resources
and conservation of marine biodiversity.
One of the characteristics of Arctic terrestrial ecosystems andbiodiversity is spatial and temporal heterogeneity (e.g. Elmendorf et al.,2012). A variety of terrestrial abiotic and biotic factors co-interact witheach other to support and form the Arctic ecosystem and these in­teractions are changing under the effects of climate change. This renders
the understanding of Arctic terrestrial biodiversity and ecosystemchanges a complex and difficult task (Callaghan and Jonasson, 1995).
Vegetation is one of the fundamental biotic parts of ecosystems as it
affects both the atmosphere and biosphere. In recent decades, tundra
shrub cover and growth in Eurasian Arctic have increased (Macias-­
Fauria et al., 2012) but a lack of adaptation to environmental conditions
that are not directly associated with climates, such as photoperiod, bi­
otic interactions or edaphic conditions, would make adaptation much
more difficult for Arctic plants in addition to the stress of climate change(Bjorkman et al., 2016).
To date, there is very limited information on microbes in the Arctic
terrestrial ecosystem due to the lack of a comprehensive survey. This isbecause a large part of the Arctic region remains inaccessible and mi­
crobes exhibit highly variable spatial and temporal heterogeneity (e.g.
Campbell et al., 2010; CAFF, 2013). Therefore, the research on
microbes—their diversity and ecophysiological characteristics—needs
to be continued and expanded as information and research on the mi­crobial diversity would greatly improve our understanding of microbial
composition and function in the Arctic ecosystem.
Arctic lakes are an important aspect of spatial heterogeneity of the
Arctic tundra ecosystem (Kling, 1995). Approximately 18–20% of theland area in the Canadian Arctic (north of 60 � N) is covered by fresh­water (Prowse and Ommanney, 1990). Global warming has impacted
Arctic lakes through the loss of ice cover or increased duration of ice-free

conditions causing the lake ecosystems to enter into a state of rapidtransition (Vincent et al., 2008, 2012; Mueller et al., 2009; Prowse et al.,2011). Therefore it is vital to monitor the lake ecosystems and under­
stand their mechanisms in response to climate change for the purposesof scientific research and conservation of Arctic ecosystems.
The goal of the Arctic Challenge for Sustainability (ArCS) Project­—an Arctic region research project initiated in Japan—is to elucidate
Arctic ecosystem responses and biodiversity alterations under current
environmental change. We conducted oceanographic and marine
ecological surveys in the northern Bering Sea, the southern Chukchi Sea
and on St. Lawrence Island, as well as terrestrial ecosystem and biodi­
versity investigations in the Canadian High Arctic (Fig. 1). This paper
provides a synthesis of the results and new findings on the Arctic
ecosystem and biodiversity that have emerged from the ArCS project.
2. Marine ecosystem
2.1. Heat flux, nutrient supply and dissolved organic matter
Rich nutrients in the Anadyr Water and Bering Shelf Water support
high primary production in the northern Bering and southern Chukchi
seas (Fig. 1) (e.g. Springer and McRoy, 1993; Grebmeier et al., 1988,
2006b). In contrast, Alaskan Coastal Water is poor in nutrients andtransports heat from south to north and huge amounts of organic matterfrom the Yukon River (e.g. Walsh et al., 1989; Eisner et al., 2013). As aresult of these recent changes in the Arctic, there is a need to have abetter understanding of the processes of nutrient supply, water mass
structure and heat flux in the Arctic.
Tsukada et al. (2018) showed that solar heating on the Chukchi shelfand heat flux from the Bering Strait may contribute to interannual
variations in heat transport from the shelf to the western Arctic Basin.
Therefore, monitoring of solar heating over the Chukchi shelf is key tounderstanding the summer sea ice retreat in the western Arctic Basin.
Moreover, sea ice production and melt play important roles in thebiogeochemical cycles. Evans and Nishioka (2018) reported thatmicronutrients and trace metals, such as iron, from shelf sediments weretransported northward through accumulation in sea ice and subsequentmelting. Evans and Nishioka (2019) also reported that sea ice formation,
chemical reduction and brine injection were the processes driving
accumulation and release of iron and other trace metals in Arctic sea ice.
These results are important for understanding responses of phyto­plankton photosynthesis in response to the reduction of Arctic sea ice.
Volatile organic iodine compounds (VOIs) contribute to ozone
depletion in the lower troposphere. Ooki et al. (2015, 2016) conducted aseries of unique studies on VOIs to examine their impacts on primaryFig. 1. Maps showing the locations of the study sites for the ArCS project. SCS: Southern Chukchi Sea, NBS: Northern Bering Sea, SLI: St. Lawrence Island, KW:
Kuujuarapik-Whapmagoostui, SA: Salluit, TS: Tremblay Sound, PI: Pond Inlet, SI: Scott Inlet, WHI/WHL: Ward Hunt Island/Lake, WG: Walker Glacier, DF: Dis­
raeli Fjord.
2

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Polar Science 27 (2021) 100533

production. Their results showed that the Arctic Ocean actively emits
VOIs to the atmosphere and the concentrations are high in the bottom
water. This suggests that the degradation of organic matter in sediments
substantially contributes to the production of VOIs in the Chukchi Sea
shelf. Tanaka et al. (2016) and Yamashita et al. (2019) further foundevidence that the dissolved organic matter (DOM) in the Bering and
Chukchi Sea waters during early summer is conservative and controlled
mainly by the mixing of water masses. They used DOM availability andoptical parameters to understand the complex water mass distribution in
the region. They developed a more precise method to distinguish water
masses, using the data from a fluorescent DOM (FDOM) sensor mounted
on a conductivity, temperature, depth (CTD) device and combined withconventional approach of temperature-salinity analysis. This improved
method is useful for understanding the formation and mixing processesof nutrient-rich water masses such as Anadyr Water.
Abe et al. (2019) deployed a mooring system with an Acoustic
Doppler Current Profiler (ADCP) and chlorophyll fluorescence–turbidity
sensor at a station in the Bering Strait to examine the impact of
locally-enhanced currents to particle transport. Their mooring data
captured a clear signal of sediment resuspension where strong local
currents exceeded 100 cm s 1. Resuspension occurred when the strong
wind-induced barotropic currents exceeded 50 cm s 1. While suspended
matter potentially contains phytoplankton in autumn, it is unlikely in
winter, suggesting the degradation of phytoplankton in the sediments
during sea ice season. These physio-biological processes may play a rolein the supply of organic materials to downstream regions and should betaken into account when estimating carbon and nutrient fluxes from theBering Sea to the Arctic Ocean, especially in response to recent changes
in heat flux and sea ice extent.

sea ice conditions.
Toxic algae, which could germinate on the surface of sediments,
were also found in waters of the Chukchi and Bering Sea shelves. Nat­suike et al. (2017a) detected vegetative cells of Alexandrium tamarenseon the shelves in summer; high densities were found mainly in warmer
waters such as in Bering Shelf Water. Densities far exceeded thoseindicating risks of paralytic shellfish poisoning (PSP), and exhibited asignificant positive correlation with water temperature (Natsuike et al.,2017b). Thus, recent and future increases in water temperature could
enhance toxic algal blooms, which, in turn, bring severe negative effects
on the various plankton feeders and higher trophic level predators,
including humans.
Zooplankton advection is one of the potential mechanisms that could
also change pelagic–benthic coupling. Amano et al. (2019) examined
spatial distributions of chaetognath abundance and community struc­ture in 1991 and 2007 and found that Eukrohnia hamata was only
recorded in the southern Chukchi Sea in 2007. They also reported thatthe water mass in the southern Chukchi Sea in 2007 was warmer thanthat in 1991 and identified this warm water mass as Alaskan Coastal
Water, based on the criteria from Danielson et al. (2017). This provides
evidence of the transport of E. hamata with Pacific water through theBering Strait. Landeira et al. (2018) reported the foremost documented
northward expansion of the planktonic larvae of the commercially
important tanner crab Chionoecetes bairdi to the Chukchi Sea in summerof 1992. In an earlier study, Landeira et al. (2017), reported that in 2007
and 2008, C. bairdi larvae were only distributed in the southern Bering
Sea and their presence had strong correlation with that of their adult
populations. Populations transported from the Bering Sea or Pacific
Ocean into the Arctic Ocean would have difficulty surviving andreproducing under the current climate conditions. Nonetheless, they
may become viable under future ocean warming. Matsuno et al. (2016),
for instance, showed that warm water temperature had a clear positiveeffect on the growth of the dominant zooplankton species (Calanus gla­
cialis) in the area. Landeira et al. (2018) further concluded that on the
Chukchi Sea shelf, water temperature that is a few degrees higher thanthe current level would lead to eventual recruitment of C. bairdi
postlarvae.
Maekakuchi et al. (2018) compared the body size and population
density of the appendicularian species Oikopleura vanhoeffeni in sum­mers of 2007 and 1983–1996. Their analyses showed an overall
decrease in the species’ body size and population density in 2007 rela­tive to 1983–1996, potentially from an earlier spawning event due toearly sea ice retreat in 2007. Nakano et al. (2016) examined the stomach
contents of polar cod caught in the northern Bering and southern
Chukchi seas in summer of 2013 and revealed that appendicularian was
the most dominant prey item in the polar cod’s diet. This highlights thetrophic importance of gelatinous zooplankton and necessitates thefurther monitoring of seasonal and interannual changes in their abun­dance and distribution.
Zooplankton distribution and abundance may be closely linked to theseasonal migration of seabirds. In particular, the short-tailed shearwater
Andenna tenuirostris, an abundant marine top predator in the Pacific, wasalso seen in the Bering Sea in spring and summer and the Chukchi Sea inautumn. Nishizawa et al. (2017) reported that A. tenuirostris distribu­
tions were concentrated in the waters where large-sized krill were moreabundant, suggesting that the changes in the zooplankton advection andsize are crucial determinants of shearwaters’ distribution. Sea ice in thenorthern Bering Sea exhibited an anomalously early retreat in the winterof 2017/2018 (Stabeno and Bell, 2019), and crested and least auklets(Aethia cristatella and A. pusilla)in St. Lawrence Island, which are also
zooplankton feeders, failed to fledge their chicks during the summer of2018 (Will et al. personal comm.).

2.2. Plankton and impact on higher trophic levels
Marine ecosystems on the Bering and Chukchi Sea shelves arecharacterized by strong pelagic–benthic coupling (Grebmeier et al.,1988) because of elevated primary production of large diatoms (icealgae and phytoplankton) and low zooplankton grazing pressure. Bothprocesses are considerably affected by sea ice extent and timing of sea
ice retreat (Grebmeier, 2012; Hunt et al., 2002). Parts of this process
were clearly identified by Waga et al. (2019) in their analysis of satellite
and long-term monitoring data of benthic biomass. They compared
optically retrieved phytoplankton size with benthic macrofaunalbiomass, and found a large northward shift in biomass and a strong
positive correlation between phytoplankton size and sediment chloro­
phyll a concentration, indicating the availability of food for the benthic
community.
Increase in the number of cyclones (McCabe et al., 2001) may also
impact this coupling process. Yokoi et al. (2016) reported that abun­dances of 11 micro-sized phytoplankton species (diatoms, di­noflagellates and ciliates) at a fixed station on the Chukchi Sea shelf
increased considerably after a strong wind event in September. Morecyclones in the future could transport nutrients from deeper layers to thesurface and enhance microplankton blooms in autumn.
Resting stage cells of diatoms in sediments have been considered to
be a seed population for the spring phytoplankton bloom (e.g. Garrison,
1984). However, little is known about these cells in the Arctic Ocean.
Tsukazaki et al. (2018) reported high densities of viable resting stage
cells of typical Arctic diatom species in sediment samples from the
Chukchi Sea. However, after being stored for 6 months in the dark, only
cells in water samples remained viable, implying that the cells in thewater samples could be potential seeds for ice algae and phytoplankton
blooms. Fukai et al. (2019) reported fluctuations in density and species
composition of resting cells. In 2018, they found that the number ofgerminating cells in sediments from the northern Bering Sea was 10–100
times that in 2017; phytoplankton and ice algae species were dominant
in 2017 and 2018, respectively. These results suggest that community
composition and abundance of resting stage cells are highly affected by

2.3. Fishery resources
Understanding responses of the distribution of fishery resources to3

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climate change is important for conservation and sustainable manage­
ment of marine species for future food supply and security (Hollowed
et al., 2013). While marine species generally exhibit climate-driven
range shifts in response to changes in water temperature (Burrows
et al., 2019), potential differences in their response could also be
attributed to non-climatic factors that are related to species-specificsensitivity and exposure to climate regimes. Alabia et al. (2018)
analyzed distribution shifts of major marine fish and invertebrate taxa
collected from bottom trawl surveys in the Bering shelf region duringlocal climate regime shifts (cool to warm and warm to cold transitions).
Using multi-model ensemble outputs, they showed that observed andmodeled rates of distribution shifts in marine taxa were poorly corre­
lated with the rate of climate change. Their results add to the increasing
evidence on the shift of marine resources and raise concerns about futureavailability of marine living resources for commercial fisheries. Distri­bution shifts of most target species trail behind climate regime shifts,
suggesting that these taxa will be unable to remain in their preferredclimatic envelopes; thus, underpins the possibility of regional species
loss in a rapidly warming ocean.
Bycatch from fishing activities also poses a serious threat to marine
life, such as the Greenland shark Somniosus microcephalus, which is alarge shark that is up to 6 m in total length and can exceed 1000 kg inbody mass. It lives in the North Atlantic and Arctic Oceans, and forages
on a variety of fish, invertebrates (e.g., squid), and marine mammals (e.
g., seal). It is considered as an apex predator in the Arctic, assuming vital
ecological roles (MacNeil et al., 2012). Greenland sharks have beenmassively harvested in the past, primarily for their liver oil. Although
Greenland shark fisheries have declined dramatically since themid-1900s, a number of sharks are still caught as bycatch in fisheries
targeting other species. As part of the ArCS project, Barkley et al. (2020)
attached sensors on the heads of Greenland sharks to investigate
swimming behavior around Baffin Island. Most tagged sharks recoveredfrom capture stress and behaved normally within a day, and no in­dividuals died following release. These results suggest that Greenland
sharks are not especially vulnerable to capture stress, if handledappropriately when caught by long-line fisheries as bycatch (e.g. cuttinga branch of the long line to release the shark quickly), and most of themthat are released back to the sea may eventually survive.

16%), Cladosporium (approximately 11%), and Mrakia (approximately
11%). Additionally, two novel yeast species from the sampling site wereisolated and described as Gelidatrema psychrophila and Mrakia arctica(Tsuji et al., 2018a, 2018b).
We also conducted studies in the area of Walker Glacier (unofficialname) (83.0 � N, 72.1 � W; Fig. 1) on the northern coast of Ellesmere Is­
land. Fungi were isolated from the melting glacier surface and the soil
exposed by glacier retreat. We sequenced the DNA of 275 fungal strains;
51 strains were classified to the genus Vishniacozyma while two strains
were identified as members of a novel species with the proposed name,Vishniacozyma ellesmerensis (Tsuji et al., 2019a). The ITS and D1/D2
domain sequences of 4 out of 111 Mrakia strains showed low similarity
to other members of known species from this genus. We subsequently
described and named these four strains as the new species, Mrakia
hoshinonis (Tsuji et al., 2019b). In summary, a total of four novel fungal
species were isolated and described from this microbial survey atEllesmere Island.
All four novel fungal species are basidiomycetous yeasts. They arecharacterized by growth at sub-zero temperatures and in vitamin-free
and amino acids-free media. These characteristics allow these species
to survive and grow in perennially cold, oligotrophic habitats in theHigh Arctic. The genus Vishniacozyma accounted for around 40% of
culturable fungi in the ice island melt pool and 19% of fungal strains
isolated from the area of Walker Glacier. Around 11% of culturable fungi
from the ice island and 40% from Walker Glacier sites belonged to thegenus Mrakia. These two genera appear to be the major mycoflora
representatives in this region. Extracellular enzyme tests indicate thatthe novel fungal species isolated from the northern part of Ellesmere
Island were able to decompose a variety of organic materials even atsubzero temperature, suggesting that they might play an important rolein the biogeochemical cycles of the ecosystems of the Canadian High
Arctic. According to the information on sequence similarity available in
the DNA Databank, these four taxa are unique species and their distri­bution is highly localized. Under the current trajectory of climatechange, these cold-dwelling fungi are highly vulnerable to habitat loss
and may become endangered. Therefore, to conserve the fungi native to
the Canadian High Arctic, large-scale microbial investigations should
continue, and a Red List of Arctic fungi should be prepared.

3. Terrestrial ecosystem

3.1.2. Plant pathogenic fungi in the Canadian sub-Arctic
Phytopathogenic fungi and fungal-like microbes have been found inplants in cold regions (Hoshino et al., 2009; Tojo and Newsham, 2012).
Some of them can act as snow rot pathogens, which causes cryophilic
fungal diseases (Hoshino et al., 2009) in many wild plants. However, theinformation on snow rot pathogens in natural, cold environments is very
limited. Therefore, it is important to understand the characteristics ofthese pathogenic fungi, including their effects on plants (Matsumoto andHsiang, 2016).
We collected snow rot pathogens from a forest tundra in
Kuujuarapik-Whapmagoostui (KW), Quebec, Canada (55 � N). From oursamples, we found snow molds (Typhula spp.) that can typically be foundas far north as the Arctic and as far south as snowy regions in thetemperate zone. In the Arctic, Typhula spp. are typically found in con­tinental rather than maritime climates (Hoshino et al., 2009) while none
was found on the Arctic coastal plants (Conners, 1967). Our study was
the first to record the distribution of Typhula sp. on coastal plants in the
sub-Arctic region. We also found sclerotia forming on the surface of deadsea peas (Lathyrus japonicus) leaves at the banks of the Great Whale River
where humidity is relatively high. Mycelia with clamp connection wereisolated from these sclerotia, and their optimal growth temperature wasfound to be around 10–15 � C. When cultured on potato dextrose agar
plates at 10 � C, they easily lost most of their sclerotium-forming ability.
Globisporangium spp., which was previously a member of the genus
Pythium, are fungal-like microbes and are widely distributed in soil andwater (van der Plaats-Niterink, 1981). Natural Globisporangium infection
in mosses in the polar regions had been recorded (Hoshino et al., 2009;

3.1. Microbial diversity in the Canadian Arctic
3.1.1. Fungal diversity in the Canadian High Arctic
The Pan-Arctic checklist of lichens and lichenicolous fungi compiledby the Conservation of Arctic Flora and Fauna (CAFF) (Kristionsson
et al., 2010) includes over 1000 species of lichens and lichenicolous
fungi from the Canadian High Arctic, of which, approximately 400
species can be found on Ellesmere Island alone. Recently, as many as 25
novel fungal taxa have been isolated from mosses collected from
Oobloyah Bay on Ellesmere Island (Osono et al., 2012). Despite thisprogress, the information about fungal diversity in the Canadian High
Arctic still remains very fragmentary and limited.
In order to fill in the research gap on fungal diversity in the High
Arctic, we conducted a microbiological survey out at Ward Hunt Island(83.0 � N, 74.1 � W) in the northern Ellesmere region (Fig. 1), with theaim to discover and isolate novel fungal species. Benthic microbial matsin a meltwater pool on an ice island in Disraeli Fjord (82.5 � N, 73.5 � W)
were sampled. Maps and further details about the sampling site aredescribed in Vincent et al. (2011). A total of 76 different fungal strains
were isolated from five different microbial mat samples and their DNA
were sequenced. On the basis of the sequences of the ITS region and theD1/D2 domain of the LSU rDNA gene, these strains were classified into
11 ascomycetous genera, 10 basidiomycetous genera and 1 zygomyce­
tous genus. Dominant fungi from the sampling site mostly belonged to
the genera Vishniacozyma (approximately 38%), Preussia (approximately
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Polar Science 27 (2021) 100533

Tojo et al., 2012) as some cold environment species from this genus canbehave as snow rot pathogens (Tojo, 2019). We conducted a moss survey
in the forests of KW, Quebec, Canada in 2016, and isolated an unknown
Globisporangium species from our samples. We tentatively named it
Globisporangium sp. strain KW5. Based on the molecular phylogenetic
identity, strain KW5 is most closely related to G. okanoganense, awell-known snow rot pathogen in Japan (Takamatsu, 1989; Takamatsu
and Takenaka, 2001) and USA (Lipps and Bruehl, 1978, 1980). Strain
KW5, therefore, has the potential to behave as a snow rot fungus.

assemblages in the Arctic (Svoboda and Henry, 1987; Callaway andWalker, 1997). Although further studies are needed to study the re­lationships between biodiversity and ecosystem functions in tundra
ecosystems (Zhu et al., 2016; Mori et al., 2017; Wang et al., 2018), theknowledge gained here acts as an important foundation andground-based evidence proving that plant communities can be sub­stantial in determining the fundamental functions of terrestrial ecosys­
tems such as carbon dynamics. Climate change can change thisecosystem balance through feedback loops between species assemblages
and their contributions towards climate stabilization.
In addition to plant diversity, we also need to shed light on otherfacets of diversity such as animals, fungi and bacteria, to know how they
are related to ecosystem functions. Life history strategies vary, butnutrient and energy cycling as a result of decomposition, and in­teractions between trophic levels may provide important contributions
to ecosystem functioning (Wallenstein et al., 2007). For example,
plant-based food web studies show that geese grazing pressure orpathogenic damage could affect the carbon balance of the ecosystem or
result in vegetation degradation (Milakovic and Jefferies, 2003; Olofs­
son et al., 2011). Similar dynamics have also been observed and reported
in the Arctic tundra (Masumoto et al., 2018). Trophic interactions be­
tween elements above and below ground may also vary on different
spatial scales, resulting in different responses in the ecosystem towards
global warming.

3.2. Terrestrial biodiversity and ecosystem functions in the Arctic
Global warming is expected to influence biodiversity and community
structure. It could introduce substantial alterations in fundamental
ecosystem functions such as primary productivity and nutrient cycling,which are currently supported by different biota (Walker et al., 2005;
Bhatt et al., 2010; Raynolds et al., 2012; Scheffer et al., 2012; CAFF,
2013; Ims et al., 2013). Local studies have shown that vegetation type
results from local environmental factors such as soil fertility and mois­
ture availability, which can determine interactions among plant species.
That vegetation structure could, in turn, lead to differences in thefunction of the ecosystem (Billings, 1973; de Molenaar, 1987; Walker
et al., 1994; Tilman et al., 1996, 2014; Grime, 1998). Understanding
how these local processes affect and determine the structure and func­
tionality of ecological communities is urgently required. This is partic­
ularly true, given the likelihood of substantial changes in carbon
dynamics in the region that can further alter climate systems through the
feedback loop between vegetation and climate. Therefore, we first aim
to gain local empirical knowledge on how biological or physiochemical
processes can shape the ecological communities and then understandhow these species assemblages can support the ecosystem functions.
Vegetational shifts are increasing in the Arctic regions due toanthropogenic climate change. For instance, studies have consistently
reported that global warming could lead to shrub expansion to thetundra vegetation, which would, in turn, lead to a short-term decline invascular plant diversity (Myers-Smith et al., 2011). However, anotherglobal analysis suggested that the forest-tundra transitions are more
likely to be controlled by non-linear (tipping-point) processes (Scheffer
et al., 2012) because tundra vegetation shift depends on local factors (e.
g. soil nutrient, biological interactions) as well as global or regional
factors (e.g. atmospheric heating, surface albedo). Compared with
regional climate changes, local factors or processes often have greater
influences on vegetation composition (Dearborn and Danby, 2017;
Nabe-Nielsen et al., 2017). We investigated vascular plant composition
and abiotic environments in the tundra–boreal forest ecotone (KW on
Fig. 1) in summer of 2016 to clarify local factors promoting shrub
expansion. The investigation revealed a positive colonizing relationshipbetween shrub species, suggesting that such local biotic interaction
could provide positive feedback to shrub expansion (Kitagawa et al.,2020).
Local factors greatly influence the relationship between biotic
properties, such as biodiversity and ecosystem functions. The impact of
local factors is particularly important in the Arctic ecosystem, which ischaracterized by the predominance of abiotic factors such as low tem­
perature and limited moisture availability that can limit the activities of
biotic organisms. To fill this knowledge gap, we identified the potential
mechanisms and functional contribution of vascular plant diversity indetermining the soil properties in the High Arctic tundra ecosystem(Mori et al., 2017). We specifically attempted to clarify the causal re­lationships between species assemblages and environmental properties,
with a focus on seral changes in species/functional diversity of vascularplants in tundra ecosystems of the High Arctic. We found that, althoughspecies richness was influenced by soil properties in the earlier stages ofprimary succession, the causalities were reversed in the later stages dueto the increase in positive interactions (facilitation) (Mori et al., 2017).
These feedbacks and interactions were important in shaping the plant

3.3. Arctic lakes
Global warming also affects the Arctic lakes resulting in losses of lake
ice, glaciers, ground ice and summer snow cover (Derksen et al., 2012).
Until recently, many lakes in the High Arctic have been covered by thickperennial ice, and their water columns have had little exchange with theatmosphere. Over past decades, several deep lakes in the Canadian High
Arctic have lost their perennial ice cover (Mueller et al., 2009; Veilletteet al., 2010), but little attention has been paid on the seasonal changes inthe High Arctic lakes. Therefore, we carried out a study to investigate
the seasonal and interannual variations between abiotic and biotic ele­ments in the northernmost lake in the Canadian High Arctic.
In 2016, 2018, joint Canada–Japan field expeditions were carried out
at Ward Hunt Lake on Ward Hunt Island (WHI; Fig. 1). In July 2016, weinstalled a mooring system at the lake to monitor its environmental
conditions with high temporal resolution throughout the year andrepeated the operation in July 2018. In July 2016, samples werecollected from the orange-pigmented microbial mat that covers thebottom of the lake, and the microbial mat was found to be dominated by
Cyanobacteria (Mohit et al., 2017). We also identified seven other spe­
cies from the mat that belonged to Basidiomycota and Ascomycota andsome species have never been recorded at the lake.
We also made the first-ever seasonal measurements of abiotic andbiotic parameters at Ward Hunt Lake. In mid-August in 2016, almost allof the ice on the surface of the lake has melted causing the lake water tobe mixed by strong winds, and water temperature in the upper layer todecrease rapidly. We found that water temperature during the following
autumn, winter and spring affected water temperature during thesummer in 2016 and the oxygen concentration was also affected by themelting of the ice cover (B�egin et al., accepted). Continuous time-series
data of chlorophyll a concentration showed that phytoplankton blooms
formed from the end of August to early September in 2016 and during
the summer in 2017. The maximum chlorophyll a concentration, which
is an index of phytoplankton biomass, was higher in 2016 than in 2017.
Higher chlorophyll a concentration of 2016 may have been caused byvertical mixing of the water column and the greater availability of lightassociated with the melting of the ice cover. Vertical mixing could
supply the whole water column with nutrients that have been accumu­
lated at the bottom of the oligotrophic lake, triggering phytoplankton
blooms. Moreover, we found that chlorophyll a concentration began toincrease in April 2017 when light intensity in the lake was still very low
5T. Hirawake et al.

Polar Science 27 (2021) 100533(B�
egin et al., accepted).
Year-round monitoring data from Ward Hunt Lake provided us withnew information on the environmental conditions at the lake during
autumn, winter and spring. We also found that seasonal environmental
conditions are affected by the summer ice cover. Data are needed to
improve our understanding of the mechanisms that could result in
pronounced ecological shifts in the High Arctic lakes under global
warming, and as some of these mechanisms could be difficult to predict,continuous monitoring should be conducted.

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4. Summary and perspectives
As part of the ArCS project, we have successfully identified oceano­graphic features including water mass structure, northward transport ofparticulate matter and processes of nutrient supply of the northern
Bering and southern Chukchi seas. We also reported on northwardtransports or shifts and considerable interannual differences inplankton, benthos, fish and seabirds, encompassing most trophic levels.
Most of these changes were related to the decline of sea ice and asso­
ciated warming in the study area over the past decades. However, ananomalously early sea ice retreat abruptly occurred in the northern
Bering Sea in winter 2017/2018, underpinning the need to further
analyze data collected from the 2017 and 2018 ArCS research cruises tobetter understand short-term responses of ocean and marine ecology.
This paper is the first review of studies of Arctic biodiversity underthe ArCS project. We found novel fungal species and a novel plant
pathogenic fungus in the sub-Arctic. We also clarified the biodiversity
and ecosystem function on a local scale using data from three sites be­
tween the sub-Arctic and the High Arctic. Our preliminary results at KW
highlight the importance of studies on local scales to evaluate and pre­dict the effects of global warming at Arctic tundra ecosystems.
The northernmost site in the ArCS project was set up at Ward Hunt
Lake in the Canadian High Arctic. Using a mooring system, we started
monitoring the lake, which is beginning to experience major environ­mental changes, to understand variations in environmental conditions
throughout the year. The data will be very important for understanding
High Arctic limnology and for contributing to other international pro­jects such as Terrestrial Multidisciplinary distributed Observatories for
the Study of Arctic Connections (T-MOSAiC, 2018) and, Sentinel North.
Our results from the ArCS project as summarized in this paper pro­vide important knowledge on present states and recent changes in the
Arctic ecosystem and biodiversity. These results contribute to the con­servation and sustainable management of Arctic ecosystem services andsupport the decision-making process of stakeholders in Arctic countries.
Further collaboration studies with social scientists are also needed.
Acknowledgements
This study was supported by the Arctic Challenge for Sustainability(ArCS) Project (Program Grant Number JPMXD1300000000), funded by
the Ministry of Education, Culture, Sports, Science, and Technology ofJapan (MEXT). We thank Tina Tin, PhD, from Liwen Bianji, Edanz Group
China (www.liwenbianji.cn/ac) and Shu Kuan Wong, PhD of the Uni­
versity of Tokyo for editing the English text of a draft of this manuscript.
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