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Symbioses between invertebrates and chemosynthetic bacteria are of fundamental importance in deep‐sea ecosystems, but the mechanisms that enable their symbiont associations are still largely undescribed, owing to the culturable difficulties of deep‐sea lives. Bathymodiolinae mussels are remarkable in their ability to overcome decompression and can be maintained successfully for an extended period under atmospheric pressure, thus providing a model for investigating the molecular basis of symbiotic interactions. Herein, we conducted metatranscriptome sequencing and gene co‐expression network analysis of Gigantidas platifrons under laboratory maintenance with gradual loss of symbionts. The results revealed that one‐day short‐term maintenance triggered global transcriptional perturbation in symbionts, but little gene expression changes in mussel hosts, which were mainly involved in responses to environmental changes. Long‐term maintenance with depleted symbionts induced a metabolic shift in the mussel host. The most notable changes were the suppression of sterol biosynthesis and the complementary activation of terpenoid backbone synthesis in response to the reduction of bacteria‐derived terpenoid sources. In addition, we detected the upregulation of host proteasomes responsible for amino acid deprivation caused by symbiont depletion. Additionally, a significant correlation between host microtubule motor activity and symbiont abundance was revealed, suggesting the possible function of microtubule‐based intracellular trafficking in the nutritional interaction of symbiosis. Overall, by analyzing the dynamic transcriptomic changes during the loss of symbionts, our study highlights the nutritional importance of symbionts in supplementing terpenoid compounds and essential amino acids and provides insight into the molecular mechanisms and strategies underlying the symbiotic interactions in deep‐sea ecosystems. [ABSTRACT FROM AUTHOR]

Bathymodiolinae mussels are dominant species in cold seeps and hydrothermal vents and could harbor endosymbionts in gill bacteriocytes. However, mechanisms underlying the symbiosis have remained largely undisclosed for years. In the present study, the global expression pattern of immune-related genes and miRNAs were surveyed in Gigantidas platifrons during bacterial challenges using enriched symbiotic methane oxidation bacteria MOBs or nonsymbiotic Vibrio. As a result, multiple pattern recognition receptors were found differentially expressed at 12 h and 24 h post bacteria challenges and distinctly clustered between stimulations. Dozens of immune effectors along with signal transducers were also modulated simultaneously during MOB or Vibrio challenge. A total of 459 miRNAs were identified in the gill while some were differentially expressed post MOB or nonsymbiotic bacteria challenge. A variety of immune-related genes were annotated as target genes of aforesaid differentially expressed miRNAs. As a result, biological processes including the immune recognition, lysosome activity and bacteria engulfment were suggested to be dynamically modulated by miRNAs in either symbiotic or nonsymbiotic bacteria challenge. It was suggested that G. platifrons mussels could maintain a robust immune response against invading pathogens while establishing symbiosis with chemosynthetic bacteria with the orchestra of immune-related genes and miRNAs. • Expression pattern of miRNAs/genes were profiled after MOB or Vibrio challenge. • PRRs and other immune genes were found distinctly clustered between the challenges. • A total of 459 miRNAs were identified in gill tissue of the deep-sea mussel. • miRNAs targeting apoptosis and phagocytosis were found responsive to challenges. • The orchestra of genes and miRNAs advantaged the immune response of deep-sea mussel. [ABSTRACT FROM AUTHOR]

Bathymodiolinae mussels are typical species in deep‐sea cold seeps and hydrothermal vents and an ideal model for investigating chemosynthetic symbiosis and the influence of high hydrostatic pressure on deep‐sea organisms. Herein, the potential influence of depressurization on DNA fragmentation and cell death in Bathymodiolinae hosts and their methanotrophic symbionts were surveyed using isobaric and unpressurized samples. As a hallmark of cell death, massive DNA fragmentation was observed in methanotrophic symbionts from unpressurized Bathymodiolinae while several endonucleases and restriction enzymes were upregulated. Additionally, genes involved in DNA repair, glucose/methane metabolism as well as two‐component regulatory system were also differentially expressed in depressurized symbionts. DNA fragmentation and programmed cell death, however, were rarely detected in the host bacteriocytes owing to the orchestrated upregulation of inhibitor of apoptosis genes and downregulation of caspase genes. Meanwhile, diverse host immune recognition receptors were promoted during depressurization, probably enabling the regain of symbionts. When the holobionts were subjected to a prolonged acclimation at atmospheric pressure, alternations in both the DNA fragmentation and the expression atlas of aforesaid genes were continuously observed in symbionts, demonstrating the persistent influence of depressurization. Contrarily, the host cells demonstrated certain tolerance against depressurization stress as expression level of some immune‐related genes returned to the basal level in isobaric samples. Altogether, the present study illustrates the distinct stress responses of Bathymodiolinae hosts and their methanotrophic symbionts against depressurization, which could provide further insight into the deep‐sea adaptation of Bathymodiolinae holobionts while highlighting the necessity of using isobaric sampling methods in deep‐sea research. [ABSTRACT FROM AUTHOR]

Heimdallarchaeia is a class of the Asgardarchaeota, are the most probable candidates for the archaeal protoeukaryote ancestor that have been identified to date. However, little is known about their life habits regardless of their ubiquitous distribution in diverse habitats, which is especially true for Heimdallarchaeia from deep-sea environments. In this study, we obtained 13 metagenome-assembled genomes (MAGs) of Heimdallarchaeia from the deep-sea cold seep and hydrothermal vent. These MAGs belonged to orders o_Heimdallarchaeales and o_JABLTI01, and most of them (9 MAGs) come from the family f_Heimdallarchaeaceae according to genome taxonomy database (GTDB). These are enriched for common eukaryote-specific signatures. Our results show that these Heimdallarchaeia have the metabolic potential to reduce sulfate (assimilatory) and nitrate (dissimilatory) to sulfide and ammonia, respectively, suggesting a previously unappreciated role in biogeochemical cycling. Furthermore, we find that they could perform both TCA and rTCA pathways coupled with pyruvate metabolism for energy conservation, fix CO2 and generate organic compounds through an atypical Wood-Ljungdahl pathway. In addition, many genes closely associated with bacteriochlorophyll and carotenoid biosynthesis, and oxygen-dependent metabolic pathways are identified in these Heimdallarchaeia MAGs, suggesting a potential light-utilization by pigments and microoxic lifestyle. Taken together, our results indicate that Heimdallarchaeia possess a mixotrophic lifestyle, which may give them more flexibility to adapt to the harsh deep-sea conditions. [ABSTRACT FROM AUTHOR]

The moon jellyfish Aurelia spp. is a worldwide distributed scyphozoan species that seasonally blooms in coastal waters. Although the strobilation is directly responsible for the scale of jellyfish bloom, the underlying mechanisms remain largely unknown. We exposed Aurelia coerulea polyps to 18 bioactive substances to test their ability to induce strobilation at the natural typically non-strobilation temperature of 21°C. Results revealed that A. coerulea polyps responded in four types. Type I—no change for estradiol, folic acid, iodine, retinoic acid, serotonin hydrochloride, and vitamin A. We suggested that 5-aza-2-deoxycytidine and N-acetyl-L-glutamic acid could not induce strobilation, since the percent of strobilated polyps in these two substances treatments was 3.3% and 1%, respectively. Type II—polyp body elongation for 3,5-diiodo-L-tyrosine, indole-3-acetic acid, L-dopamine, and noradrenaline treatments. Type III—transverse constrictions for L-thyroxine, progesterone, and melatonin treatments. Finally, Type IV—complete strobilation for 5-methoxy-2-methylindole, acetylcholine chloride, and indomethacin treatments, where the pre-strobilation periods were 2, 4, and 2 days, and the mean numbers of ephyrae released per strobila were 4.7, 5.7, and 5.7, respectively. The results reveal that indole derivatives, which contained methoxy or methyl pharmacophore, were the common strobilation inducer in the genus Aurelia. Iodinated organic compounds, catecholamine, acetylcholine chloride, and retinoic acid are species-specific strobilation inducer. Therefore, A. coerulea strobilation is regulated by neuronal and endocrine processes. Our findings provide clues in understanding the mechanism of strobilation and contribute to developing specific strobilation antagonists in controlling moon jellyfish blooms. [ABSTRACT FROM AUTHOR]

Gigantidas platifrons (Bivalvia, Mytilidae), the dominant species at the Formosa cold seep, relies on methanotrophic symbionts dwelling in its gills for nutrition. The reproductive patterns of G. platifrons provide fundamental information for understanding the population recruitment of this species. However, we know very little about important processes in reproduction, such as gametogenesis and symbiotic bacteria transmission. To this end, we described the developmental patterns of the gonads from nine surveys and juvenile length-distribution from one-year larval traps and detected bacteria in gonad from G. platifrons samples. Our results show that G. platifrons is a functionally dioecious species. The reproduction of G. platifrons is discontinuous, with spawning maturity peak around the fourth quarter of the year. The seasonal reproduction of G. platifrons was further supported by the unimodal shell length distribution of the trapped juvenile mussels. Given the small oocyte size (48.99–70.14 μm), which was comparable to that of coastal mussels, we proposed that G. platifrons developed via a free-living, planktotrophic larval stage before settlement. The blooms at the water surface can also supply the development of the planktonic larvae of G. platifrons. Meanwhile, no bacteria were observed in gonads, suggesting a horizontal symbiont transfer mode in this mussel. Collectively, these results provide fundamental biological information for an improved understanding of the early life history of G. platifrons in the Formosa cold seep. [ABSTRACT FROM AUTHOR]

As domain species in seep and vent ecosystem, Bathymodioline mussels has been regarded as a model organism in investigating deep sea chemosymbiosis. However, mechanisms underlying their symbiosis with chemosynthetic bacteria, especially how the host recognizes symbionts, have remained largely unsolved. In the present study, a modified pull-down assay was conducted using enriched symbiotic methane-oxidation bacteria as bait and gill proteins of Bathymodiolus platifrons as a target to isolate pattern recognition receptors involved in the immune recognition of symbionts. As a result, a total of 47 proteins including BpLRR-1 were identified from the pull-down assay. It was found that complete cDNA sequence of BpLRR-1 contained an open reading frame of 1479 bp and could encode a protein of 492 amino acid residues with no signal peptide or transmembrane region but eight LRR motif and two EFh motif. The binding patterns of BpLRR-1 against microbial associated molecular patterns were subsequently investigated by surface plasmon resonance analysis and LPS pull-down assay. Consequently, BpLRR-1 was found with high binding affinity with LPS and suggested as a key molecule in recognizing symbionts. Besides, transcripts of BpLRR-1 were found decreased significantly during symbiont depletion assay yet increased rigorously during symbionts or nonsymbiotic Vibrio alginolyticus challenge, further demonstrating its participation in the chemosynthetic symbiosis. Collectively, these results suggest that BpLRR-1 could serve as an intracellular recognition receptor for the endosymbionts, providing new hints for understanding the immune recognition in symbiosis of B. platifrons. • A modified MOB pull-down assay was conducted to isolate symbiosis-related PRRs. • BpLRR-1 was identified and proved with high binding affinity with LPS using SPR. • Transcripts of BpLRR-1 decreased significantly during symbionts depletion. • Robust increase of BpLRR-1 was found after symbionts or Vibrio challenge. • BpLRR-1 was suggested as an intracellular recognition receptor for MOB symbionts. [ABSTRACT FROM AUTHOR]

The Formosa Ridge, also named Site F, is an active cold seep marine ecosystem site that has been studied since it was discovered on the continental slope of the northeast South China Sea (SCS). However, few studies have focused on the eukaryotic diversity at Site F. Environmental DNA (eDNA) technology is a non-invasive method applied in biodiversity surveys with a high species detection probability. In the present study, we identified multi-trophic biodiversity using eDNA metabarcoding combined with multiple ribosomal RNA gene (rDNA) markers. We detected 142 phytoplankton, 90 invertebrates, and 64 fish species by amplifying the 18S rRNA gene V4 region, the 18S rRNA gene V9 region, and the 12S rRNA gene. The results elucidated dissimilar trends of different assemblages with depth. The diversity of phytoplankton and invertebrate assemblages markedly decreased with depth, whereas little change was observed within the fish assemblage. We comprehensively assessed the relationship between the three assemblages and environmental factors (temperature, salinity, depth, dissolved oxygen, and chlorophyll a). These factors strongly impacted on phytoplankton and invertebrates, but only slightly on fish. We inferred the finding might be due to fish having a strong migration capacity and wide distribution. This study indicates that eDNA metabarcoding with multiple markers is a powerful tool for marine biodiversity research that is able to provide technical support and knowledge for resource management and biodiversity protection efforts. • eDNA technology effectively revealed the eukaryotic diversity in the cold seep. • Distribution and diversity of multi-trophic levels varied in the vertical direction. • Environmental factors were markedly correlated with assemblage structures. [ABSTRACT FROM AUTHOR]

Abstract Deep-sea Bathymodiolus mussels depend on the organic carbon supplied by symbionts inside their gills. In this study, optimized methods of quantitative real-time PCR and fluorescence in situ hybridization targeted to both mRNA and 16S rRNA were used to investigate the gill symbionts of the cold-seep mussel Bathymodiolus platifrons , including species composition, environmental dependency and immune control by the host. Our results showed that methanotrophs were the major symbiotic bacteria in the gills of B. platifrons , while thiotrophs were scarce. In the mussels freshly collected from the deep sea, methanotrophs were housed in bacteriocytes in a unique circular pattern, and a lysosome-related gene (VAMP) encoding a vesicle-associated membrane protein was expressed at a high level and presented exactly where the methanotrophs occurred. After the mussels were reared for three months in aquaria without methane supply, the abundance of methanotrophs decreased significantly and their circle-shaped distribution pattern disappeared; in addition, the expression of VAMP decreased significantly. These results suggest that the symbiosis between B. platifrons and methanotrophs is influenced by the environment and that the lysosomal system plays an important immune role in controlling the abundance of endosymbionts in host. This study provides a reliable method for investigating symbionts in deep-sea mussels and enriches the knowledge about symbionts in B. platifrons. Highlights • qRT-PCR and FISH were used to investigate the gill symbionts of the cold-seep mussel B. platifrons. • Methanotrophs were the major gill symbionts of B. platifrons in a unique circular pattern. • Environment (i.e., methane) is critical for the maintenance of methanotrophs in B. platifrons. • The lysosomal system may play an important immunity role in controlling symbionts in B. platifrons. [ABSTRACT FROM AUTHOR]

Mussels (Bivalve: Mytilidae) have adapted to various habitats, from fresh water to the deep sea. To understand their adaptive characteristics in different habitats, particularly in the bathymodiolin mussels in deep-sea chemosynthetic ecosystems, we conducted a comparative transcriptomic analysis between deep-sea bathymodiolin mussels and their shallow-water relatives. A number of gene families related to stress responses were shared across all mussels, without specific or significantly expanded families in deep-sea species, indicating that all mussels are capable of adapting to diverse harsh environments, but that different members of the same gene family may be preferentially utilized by different species. One of the most extraordinary trait of bathymodiolin mussels is their endosymbiosis. Lineage-specific and positively selected TLRs and highly expressed C1QDC proteins were identified in the gills of the bathymodiolins, suggesting their possible functions in symbiont recognition. However, pattern recognition receptors of the bathymodiolins were globally reduced, facilitating the invasion and maintenance of the symbionts obtained by either endocytosis or phagocytosis. Additionally, various transporters were positively selected or more highly expressed in the deep-sea mussels, indicating a means by which necessary materials could be provided for the symbionts. Key genes supporting lysosomal activity were also positively selected or more highly expressed in the deep-sea mussels, suggesting that nutrition fixed by the symbionts can be absorbed in a 'farming' way wherein the symbionts are digested by lysosomes. Regulation of key physiological processes including lysosome activity, apoptosis and immune reactions is needed to maintain a stable host-symbiont relationship, but the mechanisms are still unclear. [ABSTRACT FROM AUTHOR]

The copepod Calanus sinicus Brodsky dominates the zooplankton in the Yellow Sea, China, and undergoes over-summering within the Yellow Sea Cold Water Mass (YSCWM). Termination of over-summering and subsequent development are regarded as key processes in population recruitment, and are probably linked to environmental variations in the YSCWM. In this study, we examined the effects of temperature (9 and 18°C) and food conditions (0.1 μg C mL-1 and unfed) on metabolic rates, morphological characteristics, and relative gene expressions of six genes involved in molting, gonad development, lipid catabolism, and stress tolerance processes of C. sinicus during termination of over-summering and subsequent development. Both elevated temperature and external food supply rapidly ended over-summering of C. sinicus, accompanied by up-regulation of the ecdysteroid receptor (EcR) gene expression and increased metabolic rates. These environmental conditions resulted in irreversible termination of over-summering and ensure the success of molting. During subsequent development, the lipid reserve in oil sacs could permit only early gonad development. The food supply might be a trigger to activate the final maturity of gonad by up-regulating expression of the vitellogenin receptor (VgR) gene. Thus, food played an indispensable role in population recruitment after termination of over-summering, whereas the elevated temperature accelerated these physiological processes. This study revealed the first dynamic profiles of physiological processes involved in over-summering termination and the subsequent development of C. sinicus using morphological, physiological and molecular methods simultaneously, confirmed the quiescent state of over-summering C5 copepodites, detected the effects of environmental changes on over-summering termination and subsequent development, and provided a foundation for future investigations of the mechanisms involved in over-summering in YSCWM. [ABSTRACT FROM AUTHOR]

Background: Bivalves have independently evolved a variety of symbiotic relationships with chemosynthetic bacteria. These relationships range from endo- to extracellular interactions, making them ideal for studies on symbiosis-related evolution. It is still unclear whether there are universal patterns to symbiosis across bivalves. Here, we investigate the hologenome of an extracellular symbiotic thyasirid clam that represents the early stages of symbiosis evolution. Results: We present a hologenome of Conchocele bisecta (Bivalvia: Thyasiridae) collected from deep-sea hydrothermal vents with extracellular symbionts, along with related ultrastructural evidence and expression data. Based on ultrastructural and sequencing evidence, only one dominant Thioglobaceae bacteria was densely aggregated in the large bacterial chambers of C. bisecta, and the bacterial genome shows nutritional complementarity and immune interactions with the host. Overall, gene family expansions may contribute to the symbiosis-related phenotypic variations in different bivalves. For instance, convergent expansions of gaseous substrate transport families in the endosymbiotic bivalves are absent in C. bisecta. Compared to endosymbiotic relatives, the thyasirid genome exhibits large-scale expansion in phagocytosis, which may facilitate symbiont digestion and account for extracellular symbiotic phenotypes. We also reveal that distinct immune system evolution, including expansion in lipopolysaccharide scavenging and contraction of IAP (inhibitor of apoptosis protein), may contribute to the different manners of bacterial virulence resistance in C. bisecta. Conclusions: Thus, bivalves employ different pathways to adapt to the long-term co-existence with their bacterial symbionts, further highlighting the contribution of stochastic evolution to the independent gain of a symbiotic lifestyle in the lineage. [ABSTRACT FROM AUTHOR]

DNA barcoding provides accurate identification of zooplankton species through all life stages. Single-gene-targeted metagenomic analysis based on DNA barcode databases can facilitate longterm monitoring of zooplankton communities. With the help of the available zooplankton databases, the zooplankton community of the Changjiang (Yangtze) River estuary was studied using a single-gene-targeted metagenomic method to estimate the species richness of this community. A total of 856 mitochondrial cytochrome oxidase subunit 1 (cox1) gene sequences were determined. The environmental barcodes were clustered into 70 molecular operational taxonomic units (MOTUs). Forty-two MOTUs matched barcoded marine organisms with more than 90% similarity and were assigned to either the species (similarity>96%) or genus level (similarity<96%). Sibling species could also be distinguished. Many species that were overlooked by morphological methods were identified by molecular methods, especially gelatinous zooplankton and merozooplankton that were likely sampled at different life history phases. Zooplankton community structures differed significantly among all of the samples. The MOTU spatial distributions were influenced by the ecological habits of the corresponding species. In conclusion, single-gene-targeted metagenomic analysis is a useful tool for zooplankton studies, with which specimens from all life history stages can be identified quickly and effectively with a comprehensive database. [ABSTRACT FROM AUTHOR]

Background: Despite their species abundance and primary economic importance, genomic information about copepods is still limited. In particular, genomic resources are lacking for the copepod Calanus sinicus, which is a dominant species in the coastal waters of East Asia. In this study, we performed de novo transcriptome sequencing to produce a large number of expressed sequence tags for the copepod C. sinicus. Results: Copepodid larvae and adults were used as the basic material for transcriptome sequencing. Using 454 pyrosequencing, a total of 1,470,799 reads were obtained, which were assembled into 56,809 high quality expressed sequence tags. Based on their sequence similarity to known proteins, about 14,000 different genes were identified, including members of all major conserved signaling pathways. Transcripts that were putatively involved with growth, lipid metabolism, molting, and diapause were also identified among these genes. Differentially expressed genes related to several processes were found in C. sinicus copepodid larvae and adults. We detected 284,154 single nucleotide polymorphisms (SNPs) that provide a resource for gene function studies. Conclusion: Our data provide the most comprehensive transcriptome resource available for C. sinicus. This resource allowed us to identify genes associated with primary physiological processes and SNPs in coding regions, which facilitated the quantitative analysis of differential gene expression. These data should provide foundation for future genetic and genomic studies of this and related species. [ABSTRACT FROM AUTHOR]

Background: Copepods are highly diverse and abundant, resulting in extensive ecological radiation in marine ecosystems. Calanus sinicus dominates continental shelf waters in the northwest Pacific Ocean and plays an important role in the local ecosystem by linking primary production to higher trophic levels. A lack of effective molecular markers has hindered phylogenetic and population genetic studies concerning copepods. As they are genome-level informative, mitochondrial DNA sequences can be used as markers for population genetic studies and phylogenetic studies. Results: The mitochondrial genome of C. sinicus is distinct from other arthropods owing to the concurrence of multiple non-coding regions and a reshuffled gene arrangement. Further particularities in the mitogenome of C. sinicus include low A + T-content, symmetrical nucleotide composition between strands, abbreviated stop codons for several PCGs and extended lengths of the genes atp6 and atp8 relative to other copepods. The monophyletic Copepoda should be placed within the Vericrustacea. The close affinity between Cyclopoida and Poecilostomatoida suggests reassigning the latter as subordinate to the former. Monophyly of Maxillopoda is rejected. Within the alignment of 11 C. sinicus mitogenomes, there are 397 variable sites harbouring three 'hotspot' variable sites and three microsatellite loci. Conclusion: The occurrence of the circular subgenomic fragment during laboratory assays suggests that special caution should be taken when sequencing mitogenomes using long PCR. Such a phenomenon may provide additional evidence of mitochondrial DNA recombination, which appears to have been a prerequisite for shaping the present mitochondrial profile of C. sinicus during its evolution. The lack of synapomorphic gene arrangements among copepods has cast doubt on the utility of gene order as a useful molecular marker for deep phylogenetic analysis. However, mitochondrial genomic sequences have been valuable markers for resolving phylogenetic issues concerning copepods. The variable site maps of C. sinicus mitogenomes provide a solid foundation for population genetic studies. [ABSTRACT FROM AUTHOR]

Metal pollution caused by deep-sea mining activities has potential detrimental effects on deep-sea ecosystems. However, our knowledge of how deep-sea organisms respond to this pollution is limited, given the challenges of remoteness and technology. To address this, we conducted a toxicity experiment by using deep-sea mussel Gigantidas platifrons as model animals and exposing them to different copper (Cu) concentrations (50 and 500 μg/L) for 7 days. Transcriptomics and LC-MS-based metabolomics methods were employed to characterize the profiles of transcription and metabolism in deep-sea mussels exposed to Cu. Transcriptomic results suggested that Cu toxicity significantly affected the immune response, apoptosis, and signaling processes in G. platifrons. Metabolomic results demonstrated that Cu exposure disrupted its carbohydrate metabolism, anaerobic metabolism and amino acid metabolism. By integrating both sets of results, transcriptomic and metabolomic, we find that Cu exposure significantly disrupts the metabolic pathway of protein digestion and absorption in G. platifrons. Furthermore, several key genes (e.g., heat shock protein 70 and baculoviral IAP repeat-containing protein 2/3) and metabolites (e.g., alanine and succinate) were identified as potential molecular biomarkers for deep-sea mussel's responses to Cu toxicity. This study contributes novel insight for assessing the potential effects of deep-sea mining activities on deep-sea organisms. [Display omitted] • Cu affected the immune response, apoptosis and signaling processes in G. mussels. • Cu disrupted the carbohydrate, anaerobic and amino acid metabolism in G. mussels. • Cu interfered with the pathway of protein digestion and absorption in G. mussels. • Potential biomarkers associated with Cu toxicity were identified in G. mussels. [ABSTRACT FROM AUTHOR]

The evolution of gas hydrates influenced by the seawater environment is unknown. We present a model of structural transformation from sI hydrate to sII hydrate due to the influence of seawater environment and vent fluid in nature through in situ experiments of gas hydrate formation in the Haima cold seep area. The in situ experimental results indicate that gas hydrates preferentially form as sI hydrates even in cold seep environments where C2+ hydrocarbons are present. During subsequent evolution, the sI hydrates could restructured at the effect of seawater environment and vent fluid, causing transformation to sII hydrates under the influence of hydrate stability. The supply of gas and direct contact with seawater environment are critical factors for structural transformation. Such structural transformation is the result of gas hydrates seeking thermodynamic stability and may be common in active cold seep areas. Plain Language Summary: At high pressures and low temperatures, methane molecules are able to be captured by water in a solid hydrate state, known as natural gas hydrate. The significance of the abundant reserves of natural gas hydrates in the oceans, both in terms of global climate issues and energy resources, has been widely recognised. Since most natural gas reservoirs are dominated by methane (>90%), it is generally accepted that gas hydrates in the oceans tend to be structure I. However, through a field experiment in an active cold seep area, we found that newly generated gas hydrates under the influence of the same cold seep area were of structure I, whereas naturally exposed gas hydrates that had existed for a long period of time on the seafloor were instead of structure II. Based on this, we propose a model of structural transformation (structure I to structure II) of gas hydrates under the influence of seawater environment and vent fluid. This structural transformation may be a natural phenomenon that is common in active cold seep areas. Key Points: In situ experiments have demonstrated that gas hydrates can undergo structural transformation under the influence of seawater environmentNatural structural transformations of gas hydrates are probably common, especially in active cold seep where C2+ hydrocarbons present [ABSTRACT FROM AUTHOR]

Deep-sea mining activities can potentially release metals, which pose a toxicological threat to deep-sea ecosystems. Nevertheless, due to the remoteness and inaccessibility of the deep-sea biosphere, there is insufficient knowledge about the impact of metal exposure on its inhabitants. In this study, deep-sea mussel Gigantidas platifrons, a commonly used deep-sea toxicology model organism, was exposed to manganese (100, 1 000 µg/L) or iron (500, 5 000 µg/L) for 7 d, respectively. Manganese and iron were chosen for their high levels of occurrence within deep-sea deposits. Metal accumulation and a battery of biochemical biomarkers that related to antioxidative stress in superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA); immune function in alkaline phosphatase (AKP), acid phosphatase (ACP); and energy metabolism in pyruvate kinase (PK) and hexokinase (HK) were assessed in mussel gills. Results showed that deep-sea mussel G. platifrons exhibited high capacity to accumulate Mn/Fe. In addition, most tested biochemical parameters were altered by metal exposure, demonstrating that metals could induce oxidative stress, suppress the immune system, and affect energy metabolism of deep-sea mussels. The integrated biomarker response (IBR) approach indicated that the exposure to Mn/Fe had a negative impact on deep-sea mussels, and Mn demonstrated a more harmful impact on deep-sea mussels than Fe. Additionally, SOD and CAT biomarkers had the greatest impact on IBR values in Mn treatments, while ACP and HK were most influential for the low- and high-dose Fe groups, respectively. This study represents the first application of the IBR approach to evaluate the toxicity of metals on deep-sea fauna and serves as a crucial framework for risk assessment of deep-sea mining-associated metal exposure. [ABSTRACT FROM AUTHOR]

Background: The deep-sea snail Phymorhynchus buccinoides belongs to the genus Phymorhynchus (Neogastropoda: Raphitomidae), and it is a dominant specie in the cold seep habitat. As the environment of the cold seep is characterized by darkness, hypoxia and high concentrations of toxic substances such as hydrogen sulfide (H2S), exploration of the diverse fauna living around cold seeps will help to uncover the adaptive mechanisms to this unique habitat. In the present study, a chromosome-level genome of P. buccinoides was constructed and a series of genomic and transcriptomic analyses were conducted to explore its molecular adaptation mechanisms to the cold seep environments. Results: The assembled genome size of the P. buccinoides was approximately 2.1 Gb, which is larger than most of the reported snail genomes, possibly due to the high proportion of repetitive elements. About 92.0% of the assembled base pairs of contigs were anchored to 34 pseudo‐chromosomes with a scaffold N50 size of 60.0 Mb. Compared with relative specie in the shallow water, the glutamate regulative and related genes were expanded in P. buccinoides, which contributes to the acclimation to hypoxia and coldness. Besides, the relatively high mRNA expression levels of the olfactory/chemosensory genes in osphradium indicate that P. buccinoides might have evolved a highly developed and sensitive olfactory organ for its orientation and predation. Moreover, the genome and transcriptome analyses demonstrate that P. buccinoides has evolved a sulfite-tolerance mechanism by performing H2S detoxification. Many genes involved in H2S detoxification were highly expressed in ctenidium and hepatopancreas, suggesting that these tissues might be critical for H2S detoxification and sulfite tolerance. Conclusions: In summary, our report of this chromosome-level deep-sea snail genome provides a comprehensive genomic basis for the understanding of the adaptation strategy of P. buccinoides to the extreme environment at the deep-sea cold seeps. [ABSTRACT FROM AUTHOR]

Deep-sea mussels of the subfamily Bathymodiolinae are common and numerically dominant species widely distributed in cold seeps and hydrothermal vents. During long-time evolution, deep-sea mussels have evolved to be well adapted to the local environment of cold seeps and hydrothermal vents by various ways, especially by establishing endosymbiosis with chemotrophic bacteria. However, biological processes underlying the establishment and maintenance of symbiosis between host mussels and symbionts are largely unclear. In the present study, Gigantidas platifrons genes possibly involved in the symbiosis with methane oxidation symbionts were identified and characterized by Lipopolysaccharide (LPS) pull-down and in situ hybridization. Five immune related proteins including Toll-like receptor 2 (TLR2), integrin, vacuolar sorting protein (VSP), matrix metalloproteinase 1 (MMP1), and leucine-rich repeat (LRR-1) were identified by LPS pull-down assay. These five proteins were all conserved in either molecular sequences or functional domains and known to be key molecules in host immune recognition, phagocytosis, and lysosome-mediated digestion. Furthermore, in situ hybridization of LRR-1, TLR2 and VSP genes was conducted to investigate their expression patterns in gill tissues of G. platifrons. Consequently, LRR-1, TLR2, and VSP genes were found expressed exclusively in the bacteriocytes of G. platifrons. Therefore, it was suggested that TLR2, integrin, VSP, MMP1, and LRR-1 might be crucial molecules in the symbiosis between G. platifrons and methane oxidation bacteria by participating in symbiosis-related immune processes. [ABSTRACT FROM AUTHOR]

Hypoxia, a frequent occurring threat in coastal regions, often results in mass mortalities of marine organisms and brings a serious ecological problem. The commercially important Zhikong scallop Chlamys farreri is being under such a threat as the risks of eutrophication and hypoxia have risen in their culture areas. However, little information has been known concerning their tolerance to hypoxia and their strategy for survival. In the present study, a 20-day experiment was conducted to determine the effects of hypoxia on the survival, behavior, and metabolism of Zhikong scallop. With the LC50 for dissolved oxygen (DO) being estimated as 1.8 mg/L, the survival of Zhikong scallop can be greatly challenged even under the moderate hypoxic condition of around 2.0 mg/L DO. The survival rate ranged from 69% to 59% when DO dropped from 3.0 to 2.0 mg/L, and it was further reduced to 47% at 1.5 mg/L DO. In hypoxic conditions, the scallops became significantly active, which may be explained as escape attempts to avoid hypoxic water. To save energy, Zhikong scallop would depress their respiration. However, when DO dropped from 3.0 to 2.0 mg/L, the oxygen consumption rate hardly changed. The upregulation of lactate dehydrogenase activity and the unrepressed phosphofructokinase activity, which often result in the unbalanced cellular homeostasis and energy budget, may account for the observed increase in the mortality rate of Zhikong scallops. In general, Zhikong scallop is sensitive to hypoxia events, though possible escape attempts, depressed respiration, and oxaloacetate-pathway may increase their survival chance. [ABSTRACT FROM AUTHOR]

Deep-sea hydrothermal vents in the western Pacific are increasingly explored for potential mineral extraction. The study of the composition of the food web plays an important guiding role in the ecological protection and restoration of potential mining areas. The general picture of the nutritional sources of species should be established to assess the potential impacts of future mining activities on the biological composition and food sources. To provide basic information, we analyzed the carbon and nitrogen stable isotope ratios of the dominant macrofauna (mussels, commensal scale worms, crustaceans, gastropods, and vestimentiferans) at three different sites in the PACManus hydrothermal area and the Desmos caldera. The δ13C ratio was significantly different between species: mussels and commensal scale worms showed lighter δ13C ratios, whereas crustaceans showed heavier ratios. In terms of δ15N, mussels had the lowest values and the crustaceans had the highest values. By taking into account these stable isotope signatures, we were able to develop inferences of the food sources for vent community organisms. We found that the food web was based on various species of chemoautotrophic bacteria. Mussels appeared to rely primarily on sulfur-based endosymbionts, which use the Calvin–Benson–Bassham (CBB) cycle and RuBisCO form I as the CO2-fixing enzyme. Commensal polychaetes mostly obtained their nutrition from their hosts. Crustacean species were omnivorous, feeding on chemosynthetic bacteria, sedimentary debris, or even animals according to the local environment. In contrast, gastropods relied mainly on symbiotic bacteria with some supplementary consumption of detritus. Vestimentiferans obtained food from symbiotic bacteria using the RuBisCO form II enzyme in the CBB cycle and may have several symbionts using different fixation pathways. Although most macrofauna relied on symbiotic chemoautotrophic bacteria, our study suggested a closer trophic relationship between animals. Therefore, to evaluate the potential impacts of deep sea mining, it is necessary to study the cascade effects on the food web of the whole ecosystem. Before exploiting deep-sea resources, further systematic investigations concerning the protection of deep-sea ecosystems are necessary. [ABSTRACT FROM AUTHOR]

For deep-sea hydrothermal vent crabs, recent investigations have revealed some epibiotic bacteria, but no study has described the bacterial community associated with the gill and intestine. In this study, the microbiota attached to the gill and intestine of the hydrothermal vent crab Austinograea sp. and two shallow-water crab species (Eriocheir sinensis and Portunus trituberculatus) were compared by high-throughput sequencing of 16S rDNA genes. The highest and lowest diversity in bacterial communities were observed in the gill and intestine of Austinograea sp., respectively. Non-metric multidimensional scaling (NMDS) analysis indicated that Austinograea sp. harbored a distinct microbial community. Operational taxonomic units (OTUs) for phylum Fusobacteria, class Epsilonproteobacteria, and genera Leucothrix, Polaribacter, Fusibacter, etc. were dominant in Austinograea sp. Of these, Leucothrix, Sulfurospirillum, and Arcobacter may be involved in oxidizing reduced sulfur compounds and sulfur metabolism; Marinomonas, Polaribacter adapted to the low temperature, and Fusibacter and Psychrilyobacter may survive well under hypoxic conditions. Bacteria commonly present in seawater were dominant in the gill, whereas anaerobic bacteria showed strikingly high abundance in the intestine. Interestingly, Firmicutes and Epsilonproteobacteria may complement each other in Austinograea sp., forming an internal environment. The diversified microbial community of Austinograea sp. reveals adaptation to the hydrothermal vent environment. [ABSTRACT FROM AUTHOR]

Hydrothermal systems are ubiquitous in various tectonic settings and are important in transferring internal mass and energy sources from the crust and mantle to the oceans. However, the biogeochemical processes involved in subseafloor hydrothermal circulation are not fully understood. This study investigated the compositional and isotopic properties of the high-temperature fluids collected from three hydrothermal vents of the Izena Hole in the middle Okinawa Trough in 2016 with Remotely Operated Vehicle (ROV) named Faxian. The results confirm that the latest geochemical parameters of the high-temperature hydrothermal fluids are similar to the previously reported parameters and indicate the origin of methane in the hydrothermal fluid. The nearly identical geochemistry of the three fluids indicate that they likely shared a common fluid reservoir. The endmember hydrothermal fluid contained isotopically 13C-moderate methane (− 30.4‰ to − 32.1‰), suggesting the predominance of thermogenic methane over biogenic methane incorporation in the hydrothermal fluids. The differences in the concentrations of ethane (C1/C2+ = 11,600, 5600, 970 for Faxian-1, Faxian-2, and Faxian-3, respectively) and molecular hydrogen (0.11, 0.67, and 2.4 mM for Faxian-1, Faxian-2, and Faxian-3, respectively) suggest significantly different thermal fluid-sediment interaction during the discharge stage between two hydrothermal fields. The relatively low contents of biogenic methane in all the fluids here indicated limited biogenic methane incorporation during the recharge stage due to the horizontal restriction of hydrothermal fluid circulation. The geochemical origins of methane in hydrothermal fluid and their relevance to hydrothermal fluid circulation revealed herein shed light on the different degrees of sediment influence in various geological/geographical settings in the Okinawa Trough. [ABSTRACT FROM AUTHOR]

Characterization of species diversity of zooplankton is key to understanding, assessing, and predicting the function and future of pelagic ecosystems throughout the global ocean. The marine zooplankton assemblage, including only metazoans, is highly diverse and taxonomically complex, with an estimated ~28,000 species of 41 major taxonomic groups. This review provides a comprehensive summary of DNA sequences for the barcode region of mitochondrial cytochrome oxidase I (COI) for identified specimens. The foundation of this summary is the MetaZooGene Barcode Atlas and Database (MZGdb), a new open-access data and metadata portal that is linked to NCBI GenBank and BOLD data repositories. The MZGdb provides enhanced quality control and tools for assembling COI reference sequence databases that are specific to selected taxonomic groups and/or ocean regions, with associated metadata (e.g., collection georeferencing, verification of species identification, molecular protocols), and tools for statistical analysis, mapping, and visualization. To date, over 150,000 COI sequences for ~ 5600 described species of marine metazoan plankton (including holo- and meroplankton) are available via the MZGdb portal. This review uses the MZGdb as a resource for summaries of COI barcode data and metadata for important taxonomic groups of marine zooplankton and selected regions, including the North Atlantic, Arctic, North Pacific, and Southern Oceans. The MZGdb is designed to provide a foundation for analysis of species diversity of marine zooplankton based on DNA barcoding and metabarcoding for assessment of marine ecosystems and rapid detection of the impacts of climate change. [ABSTRACT FROM AUTHOR]

Bathymodiolus platifrons adapted the chemosynthetic ecosystems, both cold seeps and hydrothermal vents, by harbouring gill symbionts. To survive these extreme and volatile ecological niches, the host mussel must be able to strictly regulate the symbionts in response to the environmental fluctuations. However, despite the research efforts, the molecular mechanisms governing host-symbiont interaction in deep-sea mussels are still largely unknown. Here, using the model deep-sea mussel Bathymodiolus plantiforns , we profiled the transcriptomic dynamic of the mussel gill during the loss and re-contact with symbionts with RNA-seq technology. The analysis of DEGs between untreated and symbiont loss samples revealed that metabolic and cellular organizational changes in the gill were associated with increased ribosomal activities, ubiquitin-proteasome systems, and autophagy. Meanwhile, the DE immune genes suggest that the host recognizes and interacts with endosymbionts through the pattern recognizing receptors, especially the Toll-like receptors. In addition, the DEGs between symbionts treated and environmental bacteria treated samples shed light on the mechanism of symbiont recognition. The symbionts treatment not only partially reversed the transcriptomic changes caused by symbiont-loss, but also suppressed host immune system which might facilitate the symbionts' entrance and survival in the host bacteriocytes. All together, these results suggest that the host-symbiont system in B. platifrons is tightly regulated but also with plasticity to fit environmental fluctuations. • First transcriptomic dynamic analysis of the deep-sea mussel Bathymodiolus platifrons gill during the loss and re-contact with symbionts. • The differentially expressed genes analysis revealed metabolic and cellular organizational changes associated with symbiont-loss. • Identified pattern recognizing receptors that might be involved in host-symbiont interaction. • Symbionts treatment could partially reverse the transcriptomic changes caused by symbiont-loss and suppress expression of host immune genes. • Identified genes that might be involved in symbiont recognition. [ABSTRACT FROM AUTHOR]

The Manila clam Ruditapes philippinarum has become a common and dominant macrobenthic species in coastal areas of the northwestern Pacific and temperate waters of Europe; it is also a major cultured shellfish, with annual worldwide production exceeding 3.3 million tonnes. This species faces greater risk of exposure to hypoxia as eutrophication worsens throughout its coastal habitats; however, its tolerance to hypoxia remains unclear, and the toxicological indicators including LC50 and LT50 have not yet been assessed. Previous studies on the effects of hypoxia on marine benthos have focused largely on functional responses, such as metabolism and gene expression, leaving potential structural damage to the mitochondria or the cells unknown. In this study we assessed the effects of hypoxia on Manila clam in terms of survival, behavior, metabolism and cellular damage, using a newly designed automated hypoxia simulation device that features exceptional accuracy and good stability. The clams exhibited strong tolerance to hypoxia as the 20-day LC50 for dissolved oxygen (DO) was estimated to be 0.57 mg L-1, and the LT50 at 0.5 mg L-1 DO was 422 hours. Adaptations included fewer buried clams and a depressed metabolism, while the unexpected rise in the activities of key enzymes involved in glycolysis may indicate a diverse strategy of shellfish under hypoxia. Cellular damage was observed as collapse of the mitochondrial cristae and both cellular and mitochondrial vacuolization. This multi-level study complements and updates our knowledge of the effects of hypoxia on marine benthos, by improving our understanding of the potential for marine ecological transformation under hypoxic conditions and providing useful information for Manila clam farming. [ABSTRACT FROM AUTHOR]

As a special type of denial of service (DoS) attacks, the TCP-targeted low-rate denial of service (LDoS) attacks have the characteristics of low average rate and strong concealment, so it is difficult to identify such attack traffic. As multifractal characteristics exist in network traffic, a new identification approach based on wavelet transform and combined neural network is proposed to classify normal network traffic and LDoS attack traffic. Wavelet energy spectrum coefficients extracted from the sampled traffic are used for multifractal analysis of traffic over different time scale. The combined neural network is designed to classify these multiscale spectrum coefficients that show different multifractal characteristics belonging to normal network traffic and LDoS attack traffic. Test results of test-bed experiments indicate that the proposed approach can identify LDoS attack traffic accurately. [ABSTRACT FROM AUTHOR]

In East Asian waters, concern about giant jellyfish blooms, including Nemopilema nomurai (Cnidaria: Scyphozoa: Rhizostomeae), has increased in recent decades. Based on surveys in 2012 and 2013, as a part of the Chinese Jellyfish 973 Program, we investigated the life cycle in situ of the planktonic stages of this species in the Yellow Sea and the East China Sea. We found the following results: (1) Offshore of the Changjiang River is one of its principal breeding places, and is the area where the pelagic stages of N. nomurai appear earliest in the YS and ECS. (2) The general distribution pattern of pelagic stages of N. nomurai described previously in the YS and ECS is confirmed from the 2012 and 2013 surveys: From this small area (31.50-33.00°N, 122.00-122.75°E) usually in late May and early June, it expanded into the 31.5-36°N sea area (aggregating in 32-34°N) in June, then continued to expand northward and southward to 30-37°N by August, and then shrank to 34-37°N in October. (3) The biomass and abundance of N. nomurai in 2012 both in June and August were higher than those in 2013. (4) We confirmed that almost all pelagic stages of N. nomurai in the YS and ECS were confined north of 30°N. The breeding places, population dynamics, and mechanism of formation of the distribution pattern of N. nomurai in the YS and ECS in recent years are presented. [ABSTRACT FROM AUTHOR]

The maintenance of physiological oxygen homeostasis is mediated by hypoxia-inducible factor (HIF), a key transcriptional factor of the PHD-HIF system in all metazoans. However, the molecular evolutionary origin of this central physiological regulatory system is not well characterized. As the earliest eumetazoans, Cnidarians can be served as an interesting model for exploring the HIF system from an evolutionary perspective. We identified the complete cDNA sequence of HIF-1α (ASHIF) from the Aurelia sp.1, and the predicted HIF-1α protein (pASHIF) was comprised of 674 amino acids originating from 2,025 bp nucleotides. A Pairwise comparison revealed that pASHIF not only possessed conserved basic helix-loop-helix (bHLH) and Per-Arnt-Sim (PAS) domains but also contained the oxygen dependent degradation (ODD) and the C-terminal transactivation domains (C-TAD), the key domains for hypoxia regulation. As indicated by sequence analysis, the ASHIF gene contains 8 exons interrupted by 7 introns. Western blot analysis indicated that pASHIF that existed in the polyps and medusa of Aurelia. sp.1 was more stable for a hypoxic response than normoxia. [ABSTRACT FROM AUTHOR]

High resolution acoustic data, together with high-definition photomosaic images and video observations of the Formosa Ridge Cold Seep Site were obtained using a remotely operated vehicle (ROV). Seabed features of the cold seep site were described in detail and the scales and distribution patterns of these features displayed on the seabed were quantitatively analyzed. The cold seep site is characterized by irregular and hummocky topography on the seabed relief map and patches with high to medium backscatter intensities on side-scan sonar (SSS) images. Based on visual data, six kinds of seabed features related to cold seep activity were identified: gas flares, dense benthic chemosynthetic communities, mussel beds with low population densities, shells and/or shell debris areas, authigenic carbonate concretions, and reduced sediments. Spatially, these seabed features are distributed in an approximately zoned pattern with gas plumes and benthic communities in the innermost part of Site F and the reduced sediments in the outermost part. Based on the integrated acoustic and visual images and in-situ geochemical data, a conceptual model describing the cold seep fluid conduits within the shallow subsurface at Site F at the present is established. Briefly, favorable conduits have developed within the authigenic carbonate mound. The conduits channelize the cold seep fluids and result in relatively focused discharge of the seep fluids at the intersections of the conduits and the seabed, to sustain the dense communities there. Additionally, the authigenic carbonate concretions redirect some of the cold seep fluids to seeps at the periphery of the site, resulting in the reduced sediments. Integrated acoustic and visual investigations combined with in situ measurements are an effective way to quantitatively study the spatial extent of a cold seep site and can provide detailed information for further study of the cold seep system. • High resolution acoustic data and visual data are used to study the Formosa Ridge cold seep site. • Seabed features associated cold seep activity and their distribution patterns at Site F are described and analyzed. • Authigenic carbonate mound is likely to both channelize and redirect the cold seep fluids. [ABSTRACT FROM AUTHOR]

Abstract: The size-fractionated zooplankton biomass, taxonomic composition, and production calculated by formulas basing on Ikeda–Motoda''s physiological methods were studied on the basis of samples taken from six cruises in the Yellow Sea. Zooplankton was size-fractionated using sieves into ~2mm, 1–2mm, 0.5–1mm, 0.25–0.5mm and 0.16–0.25mm groups. The results showed that the average zooplankton biomass was 84.03mg DM m−3 in May, followed in order by September, June, March, August and December with 42.34, 38.36, 32.37, 27.17 and 21.83mg DM m−3, respectively. The contribution of ~2mm, 1–2mm, 0.5–1mm, 0.25–0.5mm and 0.16–0.25mm groups to the total biomass was in the range of 15.2–27.4%, 13.2–29.4%, 14.7–18.2%, 15.8–22.6% and 16.3–34.2%, respectively, during the investigating period. The biomass of all size groups was all highest in May, and except that the biomass of 0.16–0.25mm group was lowest in August, the biomass of other size groups was lowest in December. The dominant zooplankton species (or taxa) in each group were similar between six cruises. The estimated zooplankton production was highest in May with 1.97mg C m−3 d−1, and was lowest in December with 0.51mg C m−3 d−1, and was in the range of 0.67–1.44mg C m−3 d−1 in other investigating months. The estimated annual zooplankton production was 0.37g C m−3 y−1. The two smallest groups aggregately comprised 59–84% of the net-zooplankton production in the Yellow Sea. The geographical distribution of size-fractionated zooplankton biomass and production was significantly affected by the complex physical features of the Yellow Sea. When the Yellow Sea Cold Bottom Water appeared from June to September, the biomass and production of zooplankton larger than 1mm were higher inside the cold water mass area than outside it, while the zooplankton smaller than 1mm showed contrary results. The higher biomass and production of all zooplankton groups occurred in the southern part of the study area in December due to the intrusion of the Yellow Sea Warm Current. And in March, the higher zooplankton biomass and production, especially for small size zooplankton, occurred at the coastal waters resulting from complex physical properties. Results of the present paper showed the biomass and production properties of size-fractionated zooplankton, which is very important for “parameterization” of food web structure models of the Yellow Sea. [Copyright &y& Elsevier]

Differences among species in prosome length and in species' response to environmental factors do exist. Therefore, it is useful to examine prosome length for different copepod species in variable environments. Seasonal variations in prosome length of four small copepods and their copepodite stages in the Jiaozhou Bay were compared and the relative influence of temperature, salinity, and chlorophyll concentration were examined. Two peaks were found in the mean prosome length of Paracalanus parvus (in early winter and May). For Acartia bifilosa, the maximum values of all copepodites occurred mainly from February to April, and decreased to the bottom in July. Prosome length of Acartia pacifica peaked when it first appeared in June, then reached to the minimum in July. Parvocalanus crassirostris only appeared from late summer to autumn and the mean prosome length showed no clear changes. Correlations of adult prosome length with environmental factors were evaluated. For the four species, temperature was negatively correlated to prosome length except for P. crassirostris. But the different species varied markedly in their responds to temperature. A. bifilosa showed a more definite trend of size variation with temperature than P. parvus and A. pacifica. Correlations of prosome length with salinity were significantly positive for almost all the small copepods. The relationship between chlorophyll concentration and prosome length was complicated for these copepods, but for P. parvus, chlorophyll concentration was also an important affecting factor. Furthermore, investigation needs to be done on food quality for some copepod. These results are essential to estimate the biomass and the production, and to understand these small copepods' population dynamics in this human-affected bay. [ABSTRACT FROM AUTHOR]

• Exposure to Cu and Cd resulted in significant metal accumulation in gills of Bathymodiolus platifrons. • Traditional biomarkers revealed cellular injury and oxidative stress in Bathymodiolus platifrons. • Metal exposure disrupted osmoregulation and both energy and nucleotide metabolism. • Different metal exposures elicited differential toxicity via differing routes. • Assessing deep-sea mining impact requires multiple sets of ecotoxicological data. Greater interest in commercial deep-sea mining has been accompanied by mounting environmental concerns, including metal contamination resulting from mining activities. However, little is known about the toxic effects of metal exposure on deep-sea life. Given its ability to accumulate metals from the surrounding environment, its wide distribution at both vents and seeps, and its high abundance, the deep-sea mussel Bathymodiolus platifrons could serve as an ideal model to investigate the toxicological responses of deep-sea organisms to metal exposure. Here, we evaluated metal accumulation, traditional metal-related biomarkers, namely acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase, catalase, reduced glutathione, metallothioneins, and malondialdehyde, as well as metabolic profiles in the gills of B. platifrons after a 7-day exposure to copper (100 μg/L), cadmium (500 μg/L), or copper-plus-cadmium treatments (100 μg/L Cu and 500 μg/L Cd). Metal exposure concentrations selected in this study can be found in deep-sea hydrothermal environments. Metal exposure resulted in significant metal accumulation in the gills of the mussel, indicating that B. platifrons has promise for use as an indicator of deep-sea metal pollution levels. Traditional biomarkers (AKP, ACP, and measured antioxidants) revealed cellular injury and oxidative stress in mussels following metal exposure. Metabolic responses in the three treatment groups indicated that metal exposure perturbed osmoregulation, energy metabolism, and nucleotide metabolism in mussels, in a response marked by differentially altered levels of amino acids, hypotaurine, betaine, succinate, glucose 6-phosphate, fructose 6-phosphate, guanosine, guanosine 5′-monophosphate, and inosine. Nevertheless, several uniquely altered metabolites were found in each treatment exposure group, suggesting dissimilar modes of toxicity between the two metal types. In the Cd-exposed group, the monosaccharide D-allose, which is involved in suppressing mitochondrial ROS production, was downregulated, a response consistent with oxidative stress in Cd-exposed B. platifrons. In the Cu-exposed group, the detected alterations in dopamine, dopamine-related, and serotonin-related metabolites together suggest disturbed neurotransmission in Cu-exposed B. platifrons. In the Cu-plus-Cd group, we detected a decline in fatty acid levels, implying that exposure to both metals jointly exerted a negative influence on the physiological functioning of the mussel. To the best of our knowledge, this is the first study to investigate changes in metabolite profiles in Bathymodiolus mussels exposed to metal. The findings reported here advance our understanding of the adverse impact of metal exposure on deep-sea life and can inform deep-sea mining assessments through the use of multiple biomarkers. [ABSTRACT FROM AUTHOR]

The active cold seep at Formosa Ridge (Site F) sustains the most flourishing ecosystem on the continental slope of the northern South China Sea. However, the physicochemical environment around the cold seep has scarcely been investigated. The knowledge about the variability of the seafloor habitat around the cold seep was poor and the key processes within the associated chemosynthetic ecosystem remain unclear. Here, we used an in situ integrated sensors detection approach combined with geochemical measurements to investigate the environmental condition around the chemosynthetic ecosystems fueled by the hydrocarbon seepage. Methane, hydrogen sulfide, dissolved oxygen and other biogenic elements in the bottom water were detected on a fine scale. The mixed gas composition and carbon isotope value of methane from the vent fluids suggested its origin was predominantly biogenic with slight thermogenic incorporation. Both horizontal and vertical variations in methane and oxygen concentrations were observed, which showed contrasting trends in fields from the center of flourishing communities to the margin of sediments. The concentration of methane decreased from 31,200 ppm at the flourishing center to 381 ppm at the margin on a horizontal gradient. The low concentration of hydrogen sulfide indicated that sulfide could be an energy-limiting factor for chemoautotrophic symbionts. The in situ oxygen levels were variable near the flourishing community but homogeneous at the margins. The results suggested that the availability of oxygen and methane played a substantial role in structuring the seep communities. Overall, from the flourishing center to the periphery, the chemical gradients drive the spatial distribution of chemosynthetic community at site F. The observations of the fine scale survey highlight the heterogeneity of microenvironments and provide novel information on the environmental dynamics within site F for the first time. • In situ detection of the fine scale environment in the cold seep were conducted. • Variations of methane and oxygen were observed from the center to the periphery. • The low sulfide level could be a limiting factor for the chemosynthetic community. [ABSTRACT FROM AUTHOR]

Deep-sea Bathymodiolus mussels are ubiquitous in most cold seeps and hydrothermal fields, where they have adapted to various toxic environments including high metal exposure. However, there is scarce knowledge of metal accumulation and metal-related biomarkers in B. mussels. Here, we present data for metal concentrations (Ag, Cd, Cr, Cu, Fe, Mn, Pb, and Zn) and metal related biomarkers (superoxide dismutase-SOD, catalase-CAT, glutathione peroxidase-GPX, glutathione-GSH, metallothioneins-MTs, and lipid peroxidation-LPO) in different tissues of B. mussels from four different deep-sea geochemical settings: one cold seep and three vent fields in the West Pacific Ocean. Results showed that mussel gills generally exhibited higher metal enrichment than the mantle. Mussels from hydrothermal vents usually had higher metal concentrations (Fe, Cr, Cd, and Pb) than those from cold seep, which could be related to their higher contents in fluids or sediments. However, despite quite different metals loads among the geochemical environment settings, Mn, Zn, and Cu concentrations varied over a smaller range across the sampling sites, implying biological regulation by deep-sea mussels for these elements. Several statistically significant correlations were observed between SOD, CAT, GSH, MTs, and metal levels in analyzed tissues. Although the vent ecosystem is harsher than the cold seep ecosystem, according to our results their mussels' biomarker levels were not so different. This finding suggests that some adaptive or compensatory mechanisms may occur in chronically polluted deep-sea mussels. Principal component analysis allowed for distinguishing different deep-sea settings, indicating that B. mussels are robust indicators of their living environments. We also compared our results with those reported for coastal mussels. To our best knowledge, this is the first integrated study to report metal accumulation and metal-related biomarkers in the deep-sea B. mussels from the West Pacific. Unlabelled Image • Vent mussels usually have higher metal levels than seep mussels. • Most biomarker levels are similar between seep and vent mussels. • B. mussels have developed special strategies to tolerate high loads of metals. • B. mussels are robust indicators of their living habitats. [ABSTRACT FROM AUTHOR]