Feasibility and usefulness of cognitive monitoring using a new home-based cognitive test in mild cognitive impairment: a prospective single arm study.

BACKGROUND: The risk of dementia is increased in subjects with mild cognitive impairment (MCI). Despite the plethora of in-person cognitive tests, those that can be administered over the phone are lacking. We hypothesized that a home-based cognitive test (HCT) using phone calls would be feasible and useful in non-demented elderly. We aimed to assess feasibility and validity of a new HCT as an optional cognitive monitoring tool without visiting hospitals. METHODS: Our study was conducted in a prospective design during 24 weeks. We developed a new HCT consisting of 20 questions (score range 0-30). Participants with MCI (n = 38) were consecutively enrolled and underwent regular HCTs during 24 weeks. Associations between HCT scores and in-person cognitive scores and Alzheimer's disease (AD) biomarkers were evaluated. In addition, HCT scores in MCI participants were cross-sectionally compared with age-matched cognitively normal (n = 30) and mild AD dementia (n = 17) participants for discriminative ability of the HCT. RESULTS: HCT had good intra-class reliability (test-retest Cronbach's alpha 0.839). HCT scores were correlated with the Mini-Mental State Examination (MMSE), verbal memory delayed recall, and Stroop test scores but not associated with AD biomarkers. HCT scores significantly differed among cognitively normal, MCI, and mild dementia participants, indicating its discriminative ability. Finally, 32 MCI participants completed follow-up evaluations, and 8 progressed to dementia. Baseline HCT scores in dementia progressors were lower than those in non-progressors (p = 0.001). CONCLUSION: The feasibility and usefulness of the HCT were demonstrated in elderly subjects with MCI. HCT could be an alternative option to monitor cognitive decline in early stages without dementia.

Insight into the latitudinal gradient of biodiversity based on spatial variations in pelagic ciliate communities along the western Arctic Ocean.

The latitudinal dynamics of biodiversity has been the focus of global attention. This study is based on the latitude gradient of biodiversity in the spatial changes of pelagic ciliate communities in the western Arctic Ocean. The gradient pattern of pelagic ciliate communities across four latitudes were investigated from the water surface at 22 sampling station in the northern Bering Sea of the western Arctic Ocean and Chukchi Sea from August 5 to August 24, 2016. Based on multivariate analyses, the results showed that (1) the spatial patterns of pelagic ciliates represented a significant latitudinal gradient along the western Arctic Ocean; (2) the species number and abundance of pelagic ciliate communities declined from 64°N to 80°N; (3) variations in the horizontal distribution of ciliates were significantly correlated with changes in physicochemical variables, especially water temperature and Chl a; Thus it is suggested that the expected latitudinal decline of biodiversity was evident along the western Arctic Ocean.

Transcriptomic Insights into Archaeal Nitrification in the Amundsen Sea Polynya, Antarctica.

Antarctic polynyas have the highest Southern Ocean summer primary productivity, and due to anthropogenic climate change, these areas have formed faster recently. Ammonia-oxidizing archaea (AOA) are among the most ubiquitous and abundant microorganisms in the ocean and play a primary role in the global nitrogen cycle. We utilized metagenomics and metatranscriptomics to gain insights into the physiology and metabolism of AOA in polar oceans, which are associated with ecosystem functioning. A polar-specific ecotype of AOA, from the "Candidatus Nitrosomarinus"-like group, was observed to be dominant in the Amundsen Sea Polynya (ASP), West Antarctica, during a succession of summer phytoplankton blooms. AOA had the highest transcriptional activity among prokaryotes during the bloom decline phase (DC). Metatranscriptomic analysis of key genes involved in ammonia oxidation, carbon fixation, transport, and cell division indicated that this polar AOA ecotype was actively involved in nitrification in the bloom DC in the ASP. This study revealed the physiological and metabolic traits of this key polar-type AOA in response to phytoplankton blooms in the ASP and provided insights into AOA functions in polar oceans.

Salinity-controlled distribution of prokaryotic communities in the Arctic sea-ice melt ponds.

The thawing of snow and sea ice produces distinctive melt ponds on the surface of the Arctic sea ice, which covers a significant portion of the surface sea ice during summer. Melt-pond salinity impacts heat transfer to the ice below and the melting rate. It is widely known that melt ponds play a significant role in heat fluxes, ice-albedo feedback, and sea-ice energy balance. However, not much attention has been given to the fact that melt ponds also serve as a unique microbial ecosystem where microbial production begins as soon as they are formed. Here, we investigated the role of melt pond salinity in controlling the diversity and distribution of prokaryotic communities using culture-dependent and -independent approaches. The 16 S rRNA gene amplicon based next generation sequencing analysis retrieved a total of 14 bacterial phyla, consisting of 146 genera, in addition to two archaeal phyla. Further, the culture-dependent approaches of the study allowed for the isolation and identification of twenty-four bacterial genera in pure culture. Flavobacterium, Candidatus_Aquiluna, SAR11 clade, Polaribacter, Glaciecola, and Nonlabens were the dominant genera observed in the amplicon analysis. Whereas Actimicrobium, Rhodoglobus, Flavobacterium, and Pseudomonas were dominated in the culturable fraction. Our results also demonstrated that salinity, chlorophyll a, and dissolved organic carbon were the significant environmental variables controlling the prokaryotic community distribution in melt ponds. A significant community shift was observed in melt ponds when the salinity changed with the progression of melting and deepening of ponds. Different communities were found to be dominant in melt ponds with different salinity ranges. It was also observed that melt pond prokaryotic communities significantly differed from the surface ocean microbial community. Our observations suggest that complex prokaryotic communities develop in melt ponds immediately after its formation using dissolved organic carbon generated through primary production in the oligotrophic water.

Electroacupuncture modulates glutamate neurotransmission to alleviate PTSD-like behaviors in a PTSD animal model.

Post-traumatic stress disorder (PTSD) is a mental disorder that develops after exposure to a traumatic event. Owing to the relatively low rates of response and remission with selective serotonin reuptake inhibitors as the primary treatment for PTSD, there is a recognized need for alternative strategies to effectively address the symptoms of PTSD. Dysregulation of glutamatergic neurotransmission plays a critical role in various disorders, including anxiety, depression, PTSD, and Alzheimer's disease. Therefore, the regulation of glutamate levels holds great promise as a therapeutic target for the treatment of mental disorders. Electroacupuncture (EA) has become increasingly popular as a complementary and alternative medicine approach. It maintains the homeostasis of central nervous system (CNS) function and alleviates symptoms associated with anxiety, depression, and insomnia. This study investigated the effects of EA at the GV29 (Yintang) acupoint three times per week for 2 weeks in an animal model of PTSD. PTSD was induced using single prolonged stress/shock (SPSS) in mice, that is, SPS with additional foot shock stimulation. EA treatment significantly reduced PTSD-like behavior and effectively regulated serum corticosterone and serotonin levels in the PTSD model. Additionally, EA treatment decreased glutamate levels and glutamate neurotransmission-related proteins (pNR1 and NR2B) in the hippocampus of a PTSD model. In addition, neuronal activity and the number of Golgi-impregnated dendritic spines were significantly lower in the EA treatment group than in the SPSS group. Notably, EA treatment effectively reduced glutamate-induced excitotoxicity (caspase-3, Bax, and pJNK). These findings suggest that EA treatment at the GV29 acupoint holds promise as a potential therapeutic approach for PTSD, possibly through the regulation of NR2B receptor-mediated glutamate neurotransmission to reduce PTSD-like behaviors.

Atlantic-origin water extension into the Pacific Arctic induced an anomalous biogeochemical event.

The Arctic Ocean is facing dramatic environmental and ecosystem changes. In this context, an international multiship survey project was undertaken in 2020 to obtain current baseline data. During the survey, unusually low dissolved oxygen and acidified water were found in a high-seas fishable area of the western (Pacific-side) Arctic Ocean. Herein, we show that the Beaufort Gyre shrinks to the east of an ocean ridge and forms a front between the water within the gyre and the water from the eastern (Atlantic-side) Arctic. That phenomenon triggers a frontal northward flow along the ocean ridge. This flow likely transports the low oxygen and acidified water toward the high-seas fishable area; similar biogeochemical properties had previously been observed only on the shelf-slope north of the East Siberian Sea.

Novel Psychopharmacological Herbs Relieve Behavioral Abnormalities and Hippocampal Dysfunctions in an Animal Model of Post-Traumatic Stress Disorder.

Post-traumatic stress disorder (PTSD) is an anxiety disorder caused by traumatic or frightening events, with intensified anxiety, fear memories, and cognitive impairment caused by a dysfunctional hippocampus. Owing to its complex phenotype, currently prescribed treatments for PTSD are limited. This study investigated the psychopharmacological effects of novel COMBINATION herbal medicines on the hippocampus of a PTSD murine model induced by combining single prolonged stress (SPS) and foot shock (FS). We designed a novel herbal formula extract (HFE) from Chaenomeles sinensis, Glycyrrhiza uralensis, and Atractylodes macrocephala. SPS+FS mice were administered HFE (500 and 1000 mg/kg) once daily for 14 days. The effects of HFE of HFE on the hippocampus were analyzed using behavioral tests, immunostaining, Golgi staining, and Western blotting. HFE alleviated anxiety-like behavior and fear response, improved short-term memory, and restored hippocampal dysfunction, including hippocampal neurogenesis alteration and aberrant migration and hyperactivation of dentate granule cells in SPS+FS mice. HFE increased phosphorylation of the Kv4.2 potassium channel, extracellular signal-regulated kinase, and cAMP response element-binding protein, which were reduced in the hippocampus of SPS+FS mice. Therefore, our study suggests HFE as a potential therapeutic drug for PTSD by improving behavioral impairment and hippocampal dysfunction and regulating Kv4.2 potassium channel-related pathways in the hippocampus.

Combined Treatment with Bojungikgi-tang (Buzhong Yiqi Decoction) and Riluzole Attenuates Cell Death in TDP-43-Expressing Cells.

OBJECTIVE: To examine the effect of combined treatment with Bojungikgi-tang (BJIGT, Buzhong Yiqi Decoction) and riluzole (RZ) in transactive response DNA-binding protein 43 (TDP-43) stress granule (SG) cells, a amyotrophic lateral sclerosis (ALS) cell line using transcriptomic and molecular techniques. METHODS: TDP-43 SG cells were pretreated with BJIGT (100 µg/mL), RZ (50 µmol/L), and combined BJIGT (100 µg/mL)/RZ (50 µmol/L) for 6 h before treatment with lipopolysaccharide (LPS, 200 µmol/L). Cell viability assay was performed to elucidate cell toxicity in TDP-43 SC cells using a cell-counting kit-8 (CCK8) assay kit. The expression levels of cell death-related proteins, including Bax, caspase 1, cleaved caspase 3 and DJ1 in TDP-43 SG cells were examined by Western blot analysis. The autophagy-related proteins, including pmTOR/mTOR, LC3b, P62, ATG7 and Bcl-2-associated athanogene 3 (Bag3) were investigated using immunofluorescence and immunoblotting assays. RESULTS: Cell viability assay and Western blot analysis showed that combined treatment with BJIGT and RZ suppressed LPS-induced cell death and expression of cell death-related proteins, including Bax, caspase 1, and DJ1 (P<0.05 or P<0.01). Immunofluorescence and immunoblotting assays showed that combined treatment with BJIGT and RZ reduced LPS-induced formation of TDP-43 aggregates and regulated autophagy-related protein levels, including p62, light chain 3b, Bag3, and ATG7, in TDP-43-expressing cells (P<0.05 or P<0.01). CONCLUSION: The combined treatment of BJIGT and RZ might reduce inflammation and regulate autophagy dysfunction in TDP-43-induced ALS.

Vertical segregation and phylogenetic characterization of archaea and archaeal ammonia monooxygenase gene in the water column of the western Arctic Ocean.

Archaea constitute a substantial fraction of marine microbial biomass and play critical roles in the biogeochemistry of oceans. However, studies on their distribution and ecology in the Arctic Ocean are relatively scarce. Here, we studied the distributions of archaea and archaeal ammonia monooxygenase (amoA) gene in the western Arctic Ocean, using the amplicon sequencing approach from the sea surface to deep waters up to 3040 m depth. A total of five archaeal phyla, Nitrososphaerota, "Euryarchaeota", "Halobacteriota," "Nanoarchaeota", and Candidatus Thermoplasmatota, were detected. We observed a clear, depth-dependent vertical segregation among archaeal communities. Ca. Thermoplasmatota (66.8%) was the most dominant phylum in the surface waters. At the same time, Nitrososphaerota (55.9%) was dominant in the deep waters. Most of the amoA gene OTUs (99%) belonged to the Nitrosopumilales and were further clustered into five subclades ("NP-Alpha", "NP-Delta", "NP-Epsilon", "NP-Gamma", and "NP-Theta"). "NP-Epsilon" was the most dominant clade throughout the water column and "NP_Alpha" showed higher abundance only in the deeper water. Salinity and inorganic nutrient concentrations were the major factors that determined the vertical segregation of archaea. We anticipate that the observed differences in the vertical distribution of archaea might contribute to the compartmentalization of dark carbon fixation and nitrification in deeper water and organic matter degradation in surface waters of the Arctic Ocean.

Arctic Ocean sediments as important current and future sinks for marine microplastics missing in the global microplastic budget.

To better understand unexpectedly low plastic loads at the ocean's surface compared with inputs, unidentified sinks must be located. Here, we present the microplastic (MP) budget for multi-compartments in the western Arctic Ocean (WAO) and demonstrate that Arctic sediments serve as important current and future sinks for MPs missing from the global budget. We identified an increase of 3% year-1 in MP deposition from sediment core observations. Relatively elevated MP abundances were found in seawater and surface sediments around the summer sea ice retreat region, implying enhanced MP accumulation and deposition facilitated by the ice barrier. We estimate 15.7 ± 2.30 × 1016 N and 0.21 ± 0.14 MT as total MP loads in the WAO with 90% (by mass) buried in the post-1930 sediments, which exceeds the global average of the current marine MP load. The slower increase in plastic burial versus production implies a lag in plastic delivery to the Arctic, indicating more pollution in the future.

Seasonal variation of inorganic carbon parameters and air-sea exchange of CO2 in Marian Cove, King George Island, Western Antarctic Peninsula.

Inorganic carbon parameters were observed in Marian Cove, King George Island, Western Antarctic Peninsula, to assess the impact of the Antarctic coastal regions on air-sea CO2 exchange. The variations in total alkalinity (TA) and dissolved inorganic carbon (DIC) were caused by ice melting, formation, and biological activities. The net annual air-sea CO2 flux (5.6 ± 11.8 mmol m-2 d-1) indicated that Marian Cove was a CO2 source in the atmosphere, suggesting the opposite role of the Antarctic coastal regions to the Southern Ocean in CO2 flux estimates. Finally, this study identified the controlling factors of the annual variation of TA and DIC for the first time through direct field observations in King George Island. This study indicated that Antarctic coastal regions can act as a CO2 source to the atmosphere. Thus, further investigations and continuous monitoring are required in the coastal areas to improve our understanding of global carbon cycles.

RNA outperforms DNA-based metabarcoding in assessing the diversity and response of microeukaryotes to environmental variables in the Arctic Ocean.

The Arctic Ocean (AO) has a harsh environment characterized by low temperatures, extensive ice coverage, and periodic freezing and melting of sea ice, which has provided diverse habitats for microorganisms. Prior studies primarily focused on microeukaryote communities in the upper water or sea ice based on environmental DNA, leaving the composition of active microeukaryotes in the diverse AO environments largely unknown. This study provided a vertical assessment of microeukaryote communities in the AO from snow and ice to sea water at a depth of 1670 m using high-throughput sequencing of co-extracted DNA and RNA. RNA extracts depicted microeukaryote community structure and intergroup correlations more accurately and responded more sensitively to environmental conditions than those derived from DNA. Using RNA:DNA ratios as a proxy for relative activity of major taxonomic groups, the metabolic activities of major microeukaryote groups were determined along depth. Analysis of co-occurrence networks showed that parasitism between Syndiniales and dinoflagellates/ciliates in the deep ocean may be significant. This study increased our knowledge of the diversity of active microeukaryote communities and highlighted the importance of using RNA-based sequencing over DNA-based sequencing to examine the relationship between microeukaryote assemblages and the responses of microeukaryotes to environmental variables in the AO.

Water Mass Controlled Vertical Stratification of Bacterial and Archaeal Communities in the Western Arctic Ocean During Summer Sea-Ice Melting.

The environmental variations and their interactions with the biosphere are vital in the Arctic Ocean during the summer sea-ice melting period in the current scenario of climate change. Hence, we analysed the vertical distribution of bacterial and archaeal communities in the western Arctic Ocean from sea surface melt-ponds to deep water up to a 3040 m depth. The distribution of microbial communities showed a clear stratification with significant differences among different water depths, and the water masses in the Arctic Ocean - surface mixed layer, Atlantic water mass and deep Arctic water - appeared as a major factor explaining their distribution in the water column. A total of 34 bacterial phyla were detected in the seawater and 10 bacterial phyla in melt-ponds. Proteobacteria was the dominant phyla in the seawater irrespective of depth, whereas Bacteroidota was the dominant phyla in the melt-ponds. A fast expectation-maximization microbial source tracking analysis revealed that only limited dispersion of the bacterial community was possible across the stratified water column. The surface water mass contributed 21% of the microbial community to the deep chlorophyll maximum (DCM), while the DCM waters contributed only 3% of the microbial communities to the deeper water masses. Atlantic water mass contributed 37% to the microbial community of the deep Arctic water. Oligotrophic heterotrophic bacteria were dominant in the melt-ponds and surface waters, whereas chemoautotrophic and mixotrophic bacterial and archaeal communities were abundant in deeper waters. Chlorophyll and ammonium were the major environmental factors that determined the surface microbial communities, whereas inorganic nutrient concentrations controlled the deep-water communities.

Anti-Inflammatory Effects of Chaenomeles sinensis Extract in an ALS Animal Model.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a systemic disease with multiple pathological effects, including neuroinflammation, oxidative stress, autophagy, mitochondrial dysfunction, and endoplasmic reticulum stress. Despite many studies seeking to identify and develop effective therapies, effective ALS treatment has yet to be approved. Hence, patients with ALS ultimately experience muscle atrophy and loss of motor neurons. Herbal medicines have been used to treat numerous diseases by modulating multiple biological processes and exerting pharmacological effects, including anti-inflammatory and antioxidant properties. In particular, Chaenomeles sinensis Koehne (CS) exhibits anti-hyperuricemic and nephroprotective effects and is used to treat anaphylaxis, viral infections, and neurodegenerative diseases, such as Alzheimer's disease. This study monitored the effects of CS supplementation on muscle function and motor neurons in hSOD1G93A mice, an established ALS animal model. METHODS: Body weight measurements and behavioral tests were performed; additionally, western blotting and immunohistochemistry analyses were conducted using the mice gastrocnemius, tibialis anterior, and spinal cord. RESULTS: CS augmented anti-inflammatory and antioxidant effects in the muscle and spinal cord of hSOD1G93A mice. Furthermore, CS improved motor function and regulated autophagy in the muscles of the hSOD1G93A mice. CONCLUSIONS: CS might represent a promising supplement for improving motor function and delaying ALS progression. However, its development for clinical use warrants further investigation.

Factors affecting the subsurface aragonite undersaturation layer in the Pacific Arctic region.

This study evaluated interannual variation in the subsurface aragonite undersaturation zone (ΩAr<1 layer) in the Pacific Arctic Ocean, using data from the 2016-2019 period. The upper boundary (DEPΩ<1UB) of the ΩAr<1 layer generally formed at a depth where the contribution of corrosive Pacific water was approximately 98 %. The intensity of the Beaufort Gyre associated with freshwater accumulation mainly determined interannual variation in DEPΩ<1UB, but the direction of its effect was opposite west and east of ~166°W. The lower boundary (DEPΩ<1LB) of the ΩAr<1 layer was generally found at a depth range where equal contributions of Pacific and Atlantic water were expected. An Atlantic-origin cold saline water intrusion event in 2017 caused by an anomalous atmospheric circulation pattern significantly lifted the DEPΩ<1LB, thus the thickness of the ΩAr<1 layer decreased.

Treatment with Herbal Formula Extract in the hSOD1G93A Mouse Model Attenuates Muscle and Spinal Cord Dysfunction via Anti-Inflammation.

Amyotrophic lateral sclerosis (ALS), a multicomplex neurodegenerative disease, has multiple underlying pathological factors and can induce other neuromuscular diseases, leading to muscle atrophy and respiratory failure. Currently, there is no effective drug for treating patients with ALS. Herbal medicine, used to treat various diseases, has multitarget effects and does not usually induce side effects. Each bioactive component in such herbal combinations can exert a mechanism of action to increase therapeutic efficacy. Herein, we investigated the efficacy of an herbal formula, comprising Achyranthes bidentata Blume, Eucommia ulmoides Oliver, and Paeonia lactiflora Pallas, in suppressing the pathological mechanism of ALS in male hSOD1G93A mice. Herbal formula extract (HFE) (1 mg/g) were orally administered once daily for six weeks, starting at eight weeks of age, in hSOD1G93A transgenic mice. To evaluate the effects of HFE, we performed footprint behavioral tests, western blotting, and immunohistochemistry to detect protein expression and quantitative PCR to detect mRNA levels in the muscles and spinal cord of hSOD1G93A mice. HFE-treated hSOD1G93A mice showed increased anti-inflammation, antioxidation, and regulation of autophagy in the muscles and spinal cord. Thus, HEF can be therapeutic candidates for inhibiting disease progression in patients with ALS. This study has some limitations. Although this experiment was performed only in male hSOD1G93A mice, studies that investigate the efficacy of HEF in various ALS models including female mice, such as mice modeling TAR DNA-binding protein 43 (TDP43) and ORF 72 on chromosome 9 (C9orf72) ALS, are required before it can be established that HEF are therapeutic candidates for patients with ALS.

Nutraceutical Interventions for Post-Traumatic Stress Disorder in Animal Models: A Focus on the Hypothalamic-Pituitary-Adrenal Axis.

Post-traumatic stress disorder (PTSD) occurs after exposure to traumatic events and is characterized by overwhelming fear and anxiety. Disturbances in the hypothalamic-pituitary-adrenal (HPA) axis are involved in the pathogenesis of mood disorders, including anxiety, PTSD, and major depressive disorders. Studies have demonstrated the relationship between the HPA axis response and stress vulnerability, indicating that the HPA axis regulates the immune system, fear memory, and neurotransmission. The selective serotonin reuptake inhibitors (SSRIs), sertraline and paroxetine, are the only drugs that have been approved by the United States Food and Drug Administration for the treatment of PTSD. However, SSRIs require long treatment times and are associated with lower response and remission rates; therefore, additional pharmacological interventions are required. Complementary and alternative medicine therapies ameliorate HPA axis disturbances through regulation of gut dysbiosis, insomnia, chronic stress, and depression. We have described the cellular and molecular mechanisms through which the HPA axis is involved in PTSD pathogenesis and have evaluated the potential of herbal medicines for PTSD treatment. Herbal medicines could comprise a good therapeutic strategy for HPA axis regulation and can simultaneously improve PTSD-related symptoms. Finally, herbal medicines may lead to novel biologically driven approaches for the treatment and prevention of PTSD.

Community assembly and co-occurrence network complexity of pelagic ciliates in response to environmental heterogeneity affected by sea ice melting in the Ross Sea, Antarctica.

In the Southern Ocean, the living environment of organisms has changed due to the dramatic increase in melting sea ice and the loss of glaciers, which have consequently caused substantial changes in biodiversity. Samples of pelagic ciliates from 13 sites were collected as bioindicators to demonstrate the relationship between spatial distribution patterns and environmental heterogeneity affected by sea ice melting and to reveal the community assembly mechanisms in the Ross Sea. Univariate analyses and multivariate analyses were effective tools demonstrating clear spatial patterns and providing a sufficient explanation to interpret strong correlations between pelagic ciliate communities and environmental variations, especially the distribution pattern of nutrients and Chl a. Moreover, environmental heterogeneity might affect the co-occurrence network complexity of ciliate communities. Furthermore, our results also indicated that stochastic processes play a significant role in the community assembly of pelagic ciliates. This study examined the controlling mechanisms of environmental heterogeneity affected by sea ice melting on pelagic ciliate communities and provided explanations for the community assembly of pelagic ciliates in polar marine ecosystems.

The Interplay of Mycosporine-like Amino Acids between Phytoplankton Groups and Northern Krill (Thysanoessa sp.) in a High-Latitude Fjord (Kongsfjorden, Svalbard).

We investigated pigment and mycosporine-like amino acid (MAA) concentrations of phytoplankton and Northern krill (Thysanoessa sp.) in sub-Arctic Kongsfjorden. Chlorophyll a (Chl-a) concentrations in the surface and middle-layer water were 0.44 µg L-1 (±0.17 µg L-1) and 0.63 µg L-1 (±0.25 µg L-1), respectively. Alloxanthin (Allo, a marker of cryptophytes) was observed at all stations, and its mean values for surface and middle-layer water were 0.09 µg L-1 (±0.05 µg L-1) and 0.05 (±0.02 µg L-1), respectively. The mean MAA-to-Chl-a ratios at the surface (3.31 ± 2.58 µg (µg Chl-a)-1) were significantly higher than those in the middle-layer water (0.88 ± 0.49 µg (µg Chl-a)-1), suggesting that these compounds play an important role in reducing UV photodamage. In gut pigment levels of Northern krill, the most abundant accessory pigment was Allo (2.79 ± 0.33 µg g-1 dry weight; d.w.), as was the accumulation of Chl-a (8.29 ± 1.13 µg g-1 d.w.). The average concentration of MAAs was 1.87 mg g-1 d.w. (±0.88 mg g-1 d.w.) in krill eyes, which was higher than that in all other body parts (0.99 ± 0.41 mg g-1 d.w.), except for the gut. Thysanoessa sp. was found to contain five identified MAAs (shinorine, palythine, porphyra-334, mycosporine-glycine, and M-332) in the krill eye, whereas shinorine and porphyra-334 were only observed in the krill body, not the eyes and gut. These findings suggest that Northern krill accumulate MAAs of various compositions through the diet (mainly cryptophytes) and translocate them among their body parts as an adaptation for photoprotection and physiological demands.

Spatial dynamics of active microeukaryotes along a latitudinal gradient: Diversity, assembly process, and co-occurrence relationships.

Recent global warming is profoundly and increasingly influencing the Arctic ecosystem. Understanding how microeukaryote communities respond to changes in the Arctic Ocean is crucial for understanding their roles in the biogeochemical cycles of nutrients and elements. Between July 22 and August 19, 2016, during cruise ARA07, seawater samples were collected along a latitudinal transect extending from the East Sea of Korea to the central Arctic Ocean. Environmental RNA was extracted and the V4 hypervariable regions of the reverse transcribed SSU rRNA were amplified. The sequences generated by high throughput sequencing were clustered into zero-radius OTUs (ZOTUs), and the taxonomic identities of each ZOTU were assigned using SINTAX against the PR2 database. Thus, the diversity, community composition, and co-occurrence networks of size fractionated microeukaryotes were revealed. The present study found: 1) the alpha diversity of pico- and nano-sized microeukaryotes showed a latitudinal diversity gradient; 2) three distinct communities were identified, i.e., the Leg-A, Leg-B surface, and Leg-B subsurface chlorophyll a maximum (SCM) groups; 3) distinct network structure and composition were found in the three groups; and 4) water temperature was identified as the primary factor driving both the alpha and beta diversities of microeukaryotes. This study conducted a comprehensive and systematic survey of active microeukaryotes along a latitudinal gradient, elucidated the diversity, community composition, co-occurrence relationships, and community assembly processes among major microeukaryote assemblages, and will help shed more light on our understanding of the responses of microeukaryote communities to the changing Arctic Ocean.