Deep-sea Ecosystems Research Articles

Characteristics of deep-sea microbial cellulases: key determinants of the ultimate fate of plant biomass on Earth

AbstractLand plants, especially those with significant woody biomass, represent the largest source of biomass on Earth, making the biodegradation of lignocellulosic materials critical to understanding the global carbon cycle. Cellulose, a major component of lignocellulose, is notoriously resistant to degradation due to its highly crystalline structure. While the degradation of cellulose by terrestrial microbes has been extensively studied, the mechanisms of cellulose degradation in deep-sea environments remain largely unexplored. The deep-sea ecosystem depends on organic matter, such as cellulose, that is synthesized in terrestrial environments and surface waters and descends to the deep sea. Recent studies suggest that a significant amount of cellulose is likely to reach the deep sea. Here, we present an in-depth study of cellulases from a novel deep-sea γ-proteobacterial strain TOYAMA8, isolated from Toyama Bay, Japan, using Surface Pitting Observation Technology (SPOT), a highly sensitive assay for enzymatic cellulose hydrolysis. The cellulases of strain TOYAMA8 show similarities to those of a previously reported deep-sea cellulolytic microbe, Marinagarivorans cellulosilyticus strain GE09. Genomic and transcriptomic analyses of these strains reveal novel cellulase genes and mechanisms that differ from terrestrial counterparts, shedding light on the unique adaptations of deep-sea microbes to recalcitrant biomass. In particular, these strains produce high-molecular-weight cellulases with unique domain architectures, likely optimized for membrane anchoring, which prevents enzyme diffusion and ensures efficient localized activity. Our findings provide critical insights into the microbial cellulose degradation in the deep sea, highlighting its role in the fate of organic carbon and the potential for biotechnological applications in biorefineries.

Influence of microplastics on the structure and function of deep-sea communities during long-term enrichment processes

Influence of microplastics on the structure and function of deep-sea communities during long-term enrichment processes

Revealing the metabolic potential and environmental adaptation of nematophagous fungus, Purpureocillium lilacinum, derived from hadal sediment

The extreme environment shapes fungi in deep-sea sediments with novel metabolic capabilities. The ubiquity of fungi in deep-sea habitats supports their significant roles in these ecosystems. However, there is limited research on the metabolic activities and adaptive mechanisms of filamentous fungi in deep-sea ecosystems. In this study, we investigated the biological activities, including antibacterial, antitumor and nematicidal activity of Purpureocillium lilacinum FDZ8Y1, isolated from sediments of the Mariana Trench. A key feature of P. lilacinum FDZ8Y1 was its tolerance to high hydrostatic pressure (HHP), up to 110 MPa. We showed that HHP affected its vegetative growth, development, and production of secondary metabolites, indicating the potential for discovering novel natural products from hadal fungi. Whole-genome sequencing of P. lilacinum FDZ8Y1 revealed the metabolic potential of this piezotolerant fungus in carbon (carbohydrate metabolism), nitrogen (assimilatory nitrate reduction and protein degradation) and sulfur cycling processes (assimilatory sulfate reduction). Transcriptomic analysis under elevated HHP showed that P. lilacinum FDZ8Y1 may activate several metabolic pathways and stress proteins to cope with HHP, including fatty acid metabolism, the antioxidant defense system, the biosynthetic pathway for secondary metabolites, extracellular enzymes and membrane transporters. This study provides valuable insights into the metabolic potential and adaptation mechanisms of hadal fungi to the challenging conditions of the hadal environment.

Deep-Sea Fauna Segmentation: A Comparative Analysis of Convolutional and Vision Transformer Architectures at Lucky Strike Vent Field

Abstract. Due to recent technological developments, the acquisition and availability of deep-sea imagery has increased exponentially in the last years, leading to an increasing backlog in image annotation and processing, attributable to limited specialized human resources. In this work, we investigate the performance of well-established convolutional neural networks and Vision Transformer (ViT) based architectures, namely, DeepLabv3+ and UNETR, for the segmentation of fauna in deep-sea images. The dataset consists of images captured at the Lucky Strike Vent field, located on the mid-Atlantic ridge, of three edifices named Montsegur, White Castle, and Eiffel Tower. Our experimental investigation reveals that the Vision Transformer consistently outperforms the fully convolutional deep learning architecture, by approximately 14% in terms of F1-Score, demonstrating the effectiveness of ViTs in capturing intricate patterns and long-range dependencies present in deep-sea imagery. Our findings highlight the potential of ViTs as a promising approach for accurate semantic segmentation in challenging environmental contexts, paving the way for improved understanding and analysis of deep-sea ecosystems.

Community composition and distribution of epi- and suprabenthic macrofauna in the bathyal, abyssal, and hadal zones of the northern North Pacific

The deep sea, Earth’s largest biome, harbors numerous unknown species. Prior to the AleutBio (Aleutian Trench Biodiversity Studies) expedition from July to September 2022, the Northeast (NE) Pacific at abyssal and hadal depths was virtually unexplored. Our study presents new findings from the AleutBio project on the macrofaunal composition of the Bering Sea (BS) and Aleutian Trench (AT) collected by means of an epibenthic sledge (EBS), comparing these results with data from the Kuril-Kamchatka Trench (KKT) and the Northwest (NW) Pacific. Additionally, we examine variations in macrofaunal composition and abundance across different regions and depths. A biogeographic gap analysis using data from the Ocean Biodiversity Information System (OBIS) and the Global Biodiversity Information Facility (GBIF) found that, out of 170,627 occurrence records from the North Pacific and Bering Sea, only 153 were from depths below 3,500 m. The AleutBio project addressed this gap by significantly expanding the dataset with 36,499 new records collected during the expedition using an EBS. Nearly 98 % of the specimens were from five phyla: Arthropoda, Annelida, Mollusca, Echinodermata, and Nematoda, with Polychaeta, Copepoda, and Nematoda being the most abundant taxa. Although the number of individuals varied between stations, there was no significant decrease in abundance with increasing depth, and some hadal stations had similar numbers of invertebrates as abyssal stations. Regional differences were observed, with Polychaeta and Nematoda being dominant in the BS, and Copepoda more prevalent at western abyssal stations. Depth emerged as the key factor influencing macrofaunal distribution, with distinct patterns across bathyal, abyssal, and hadal depths. Comparisons with other NW Pacific regions, like the Sea of Japan and Sea of Okhotsk, show that depth and water body isolation play crucial roles in shaping faunal communities. AleutBio’s extensive sampling below 3,500 m has vastly increased available data, aiding in the understanding and conservation of deep-sea biodiversity. While certain taxa showed patchy distributions, no significant differences in faunal composition were found between geographic areas or depth zones. These findings underscore the dynamic nature of deep-sea ecosystems and highlight the importance of depth in shaping macrofaunal communities, emphasizing the need for continued research in these fascinating environments.

Metagenomic analysis of deep-sea bacterial communities in the Makassar and Lombok Straits

The extreme conditions of the deep-sea environment, including limited light, low oxygen levels, high pressure, and nutrient scarcity, create a natural habitat for deep-sea bacteria. These remarkable microorganisms have developed unique strategies to survive and adapt to their surroundings. However, research on the diversity of deep-sea bacteria, both culture-dependent and culture-independent, in Indonesian waters remains insufficient. This study focused on exploring the biodiversity of deep-sea bacteria, specifically in the Makassar and Lombok Strait, the main Indonesian throughflow pathway characterized by relatively fertile water, which serves as an important deep-sea region. High-throughput DNA sequencing of full-length 16S rRNA was employed to construct a genomic database. The results of the bioinformatic analysis revealed that two stations, 48 and 50 (Makassar Strait), exhibited a more similar community structure of deep-sea bacteria than did station 33 (Lombok Strait). Among the predominant phyla found at a depth of 1000 m, the top ten were Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Planctomycetes, Acidobacteria, Nitrospinae, Verrucomicrobia, Candidatus Melainabacteria, and Cyanobacteria. Furthermore, the genera Colwellia, Moritella, Candidatus Pelagibacter, Alteromonas, and Psychrobacter consistently appeared at all three stations, albeit with varying relative abundance values. These bacterial genera share common characteristics, such as psychrophilic, halophilic, and piezophilic tendencies, and are commonly found in deep-sea ecosystem. The environmental conditions at a depth of 1000 m were relatively stable, with an average pressure 10 MPa, temperature 4.68 °C, salinity 34.58 PSU, pH 8.06, chlorophyll-a 0.29 µg/L, nitrate 3.19 µmol/L, phosphate 6.32 µmol/L and dissolved oxygen (DO) 2.90 mg/L. The bacterial community structures at the three sampling stations located at the same depth (1000 m) exhibited similarities, as indicated by the closely aligned similarity index values.

Fishes Associated with a Vulnerable Marine Ecosystem Network in the Central Mediterranean Sea

In order to collect information on ichthyofauna of a deep-sea vulnerable marine ecosystem (VME) network along the Apulian margin (central Mediterranean Sea), two low-impact sampling tools were used in three VMEs characterized by cold-water corals (CWC), namely Bari Canyon (BC), off Monopoli (Mn), and off Santa Maria di Leuca (SML). Using an experimental longline, 53 deployments were carried out between a 314 and 650 m depth for a total of 217 fishing hours, whereas when using the baited lander MEMO (Marine Environment MOnitoring system), 31 deployments were carried out between 427 and 792 m, for a total of 223 h of video recordings. A total of 37 taxa were recorded, comprising 13 Chondrichthyes and 24 Osteichthyes. The similarities in species observed among the VMEs confirm the presence of a network of CWC-VMEs along the Apulian margin, whereas some differences detected are due to the different abundance of some species, such as Galeus melastomus, Helicolenus dactylopterus, and Phycis blennoides. The presence of commercial species, vulnerable/endangered cartilaginous fishes, and large and sexually mature individuals of G. melastomus, H. dactylopterus, and Pagellus bogaraveo in all the VMEs confirms that the network of CWC-VMEs along the Apulian margin can act as a network of refuge areas and an essential fish habitat (EFH) for species threatened by fishing activities.

Cold-water coral mortality under ocean warming is associated with pathogenic bacteria

Cold-water corals form vast reefs that are highly valuable habitats for diverse deep-sea communities. However, as the deep ocean is warming, it is essential to assess the resilience of cold-water corals to future conditions. The effects of elevated temperatures on the cold-water coral Lophelia pertusa (now named Desmophyllum pertusum) from the north-east Atlantic Ocean were experimentally investigated at the holobiont level, the coral host, and its microbiome. We show that at temperature increases of + 3 and + 5 °C, L. pertusa exhibits significant mortality concomitant with changes in its microbiome composition. In addition, a metagenomic approach revealed the presence of gene markers for bacterial virulence factors suggesting that coral death was due to infection by pathogenic bacteria. Interestingly, different coral colonies had different survival rates and, colony-specific microbiome signatures, indicating strong colony-specific variability in their response to warming waters. These results suggest that L. pertusa can only survive a long-term temperature increase of < 3 °C. Therefore, regional variations in deep-sea temperature increase should be considered in future estimates of the global distribution of cold-water corals.

New species and records of limpets (Mollusca, Gastropoda) from the Pacific Costa Rica Margin.

The ocean remains a reservoir of unknown biodiversity, particularly in the deep sea. Chemosynthesis-based ecosystems, such as hydrothermal vents and hydrocarbon seeps, host unique and diverse life forms that continue to be discovered and described. The present study focuses on patelliform gastropods (limpets) collected from Pacific Costa Rica Margin hydrocarbon seeps during three research cruises from 2017 to 2019. Genetic and morphological analyses revealed the presence of several new lineages within the genera Bathyacmaea Okutani, Tsuchida & Fujikura,1992, Cocculina Dall, 1882, Paralepetopsis McLean, 1990, and the family Lepetodrilidae McLean, 1988: Bathyacmaealevinae sp. nov., Paralepetopsisvariabilis sp. nov., Pseudolepetodriluscostaricensis gen. et sp. nov., and Cocculinamethana sp. nov. These investigations also expanded the known ranges of the species Pyropeltacorymba McLean, 1992 and Lepetodrilusguaymasensis McLean, 1988 to the Costa Rica Margin. This research highlights the uniqueness of gastropod fauna at the Costa Rica Margin and contributes to our understanding of the biodiversity at chemosynthesis-based deep-sea ecosystems in the face of global biodiversity loss and increased commercial interest in deep-sea resources.

Fixation behavior of oceanic manganese nodule-sodium alginate composite microspheres for heavy metal release during manganese nodule mining

Research on the environmental impact of deep-sea mining is crucial, particularly for fragile deep-sea ecosystems. This research focuses on the issue of heavy metal release during mining activities. Through simulation experiments, we investigated the release of Cu2+, Co2+, and Ni2+ from sediments under disturbance conditions and the fixation behavior during the deployment of ocean manganese nodule-sodium alginate composite microspheres (OMN@SA). The experimental results revealed that mining disturbances cause the release of 0.291% of Cu2+, 7.34% of Co2+, and 4.13% of Ni2+ from sediments into the water, primarily in the form of exchangeable metals. Compared with the bottom adsorption, OMN@SA has a faster adsorption rate in the slow settling process. The removal rates of Cu2+, Co2+ and Ni2+ reached 54.0%, 78.3% and 61.8% for 5 h adsorption, and the bottom adsorption removal rates reached 96.4%, 97.8% and 95.1% for 30 d adsorption, which has a good removal effect. In addition, OMN@SA can effectively block the diffusion of Cu2+, Co2+, and Ni2+ from interstitial water to overlying water, and reduce the influence of interstitial water on overlying water. SEM-EDS, FTIR, and XRD analyses revealed that OMN@SA adsorbs heavy metal ions through its abundant -OH groups and incorporates Cu2+, Co2+, and Ni2+ into the crystal lattices of vernadite and todorokite via substitution or intercalation. This study provides guidance for the remediation of heavy metal release from deep-sea mining using adsorption methods and demonstrates the promising application prospects of OMN@SA.

Biotransformations of arsenic in marine sediments across marginal slope to hadal zone

Arsenic compounds are accumulating in deep ocean, but their ecological impacts on deep-sea ecosystem remain elusive. We studied 32 sediment cores (101 layers for metagenomes, along with 41 global reference sediment metagenomes) collected from the South China Sea and the Mariana Trench (MT), characterized with high arsenic accumulation in MT. In these metagenomes we revealed a significantly positive correlation between relative abundance of arsenite methyltransferase gene (arsM) and sampling depth, which suggests that arsenic methylation is the most prevalent arsenic biotransformation process in the deep sea. Lower relative abundance of arsenic efflux gene, compared with arsM, indicates that microbes in deep-sea sediments were prone to methylate arsenite and retain it rather than efflux it. Phylogenetic analysis identified seven clades of ArsM proteins, including two new clades derived primarily from deep-sea microorganisms. Five metagenome-assembled genomes containing aioA for arsenite oxidation also harbor carbon fixation genes in the deep-sea sediment layers, suggesting previously unnoticed contribution of arsenite-oxidizing autotrophic bacteria to the carbon cycle. Therefore, deep-sea microorganisms adopt different detoxification and transformation strategies in response to arsenic compounds, which renews our understanding of arsenic in their ecological impacts and potential contribution in deep ocean.

Drivers of trophodynamics of the open-ocean and deep-sea environments of the Azores, NE Atlantic

Marine ecosystems associated with mid-oceanic elevations harbour unique pelagic and benthic biodiversity and sustain food webs critical for Nature’s contributions to people (NCP). The United Nations Sustainable Development Goals and the Convention on the Law of the Sea recognize the need to implement ecosystem-based management approaches to conserve the structure and functioning of oceanic and deep-sea ecosystems within sustainable reference points. However, uncertainties regarding the interactions between multiple drivers of change, and their impacts on the state of these ecosystems and the NCP, present significant challenges to effective management. Trophic models offer a holistic approach to identify the main drivers affecting the dynamics of marine ecosystems. Here, we used a food web model of the open-ocean and deep-sea environments of the Azores for identifying the drivers that best explain historical biomass trends of demersal fish of high commercial value. Our hindcast simulations suggested that historical trends can be explained by the combined effects of deep-sea fisheries exploitation and variability in environmental conditions, likely dominated by primary productivity anomalies. In particular, deficits in primary production and high levels of fishing exploitation might have contributed to the pronounced decline in biomass observed between 2008 and 2012. These findings reinforce that failure to consider environmental factors in ecosystem-based management may result in shortfalls at achieving biodiversity conservation and sustainability objectives, particularly in the context of climate change.

Evidence for seasonal migration by a cryptic top predator of the deep sea

BackgroundIn ecosystems influenced by strong seasonal variation in insolation, the fitness of diverse taxa depends on seasonal movements to track resources along latitudinal or elevational gradients. Deep pelagic ecosystems, where sunlight is extremely limited, represent Earth’s largest habitable space and yet ecosystem phenology and effective animal movement strategies in these systems are little understood. Sperm whales (Physeter macrocephalus) provide a valuable acoustic window into this world: the echolocation clicks they produce while foraging in the deep sea are the loudest known biological sounds on Earth and convey detailed information about their behavior.MethodsWe analyze seven years of continuous passive acoustic observations from the Central California Current System, using automated methods to identify both presence and demographic information from sperm whale echolocation clicks. By integrating empirical results with individual-level movement simulations, we test hypotheses about the movement strategies underlying sperm whales’ long-distance movements in the Northeast Pacific.ResultsWe detect foraging sperm whales of all demographic groups year-round in the Central California Current System, but also identify significant seasonality in frequency of presence. Among several previously hypothesized movement strategies for this population, empirical acoustic observations most closely match simulated results from a population undertaking a “seasonal resource-tracking migration”, in which individuals move to track moderate seasonal-latitudinal variation in resource availability.DiscussionOur findings provide evidence for seasonal movements in this cryptic top predator of the deep sea. We posit that these seasonal movements are likely driven by tracking of deep-sea resources, based on several lines of evidence: (1) seasonal-latitudinal patterns in foraging sperm whale detection across the Northeast Pacific; (2) lack of demographic variation in seasonality of presence; and (3) the match between simulations of seasonal resource-tracking migration and empirical results. We show that sperm whales likely track oceanographic seasonality in a manner similar to many surface ocean predators, but with dampened seasonal-latitudinal movement patterns. These findings shed light on the drivers of sperm whales’ long-distance movements and the shrouded phenology of the deep-sea ecosystems in which they forage.

Effects of increased temperature and altered POC composition on a bathyal macrofaunal community in Cabo Verde, NE Atlantic

Deep-sea ecosystems are particularly important to the cycling of matter and energy in the oceans and therefore in regulating Earth’s climate. The Atlantic Ocean is already experiencing significant abiotic changes, with expected warmer temperatures coupled with decreased particulate organic carbon (POC) export flux. However, there is yet a large gap in our understanding of warming impacts on deep benthic ecosystems and in the organic matter processing by benthic organisms in the seafloor. This study employed an experimental approach to assess the single and cumulative effects of two climate change stressors, temperature and POC quality, on macrofaunal benthic assemblages in the Cabo Verde Basin (CVB, Equatorial Atlantic) bathyal continental slope. Incubation enrichment experiments with 13C and 15N labelled diatoms Phaeodactylum tricornutum simulated climate projections for the next century with a balanced design, studying the effect of either increased temperature (+2°C), reduced POC quality (dialysed labile fraction), or both, against a control treatment. We found that echinoderms and polychaetes rapidly ingested labelled algae at rates between 0.02 and 21.9 µg C m−2 d-1. Given a strong spatial variability in macrofaunal biomass, the carbon and nitrogen incorporation by macrofauna was not affected by a + 2 °C warming, by a decreased organic matter quality, or the combination of both factors. Our study provides valuable insights into the biodiversity, biomass, and ecosystem functioning (C and N uptake rates) of deep-sea benthic ecosystems in the N Atlantic, and stress that potential effects of warmer temperatures and POC quality on carbon and nitrogen incorporation by macrofauna remain uncertain. We highlight the value of these experiments to better understand the effects of climate change on deep-sea ecosystems.

Eucarid and Peracarid Fauna of the Valencia Seamount, a Deep-Isolated Seamount of the Western Mediterranean: Colonisation Capacity and Historical Changes

Seamounts can have a strong influence on the distribution and diversity of species, creating an oasis effect that may favour diversification. In order to assess how and to what extent supra- and epibenthic crustaceans can colonise these environments, the eucarid and peracarid fauna collected from the summit of the Valencia Seamount (VS), a small deep seamount (summit depth: 1056 m), rising from a depth of ca. 1850 m, in the oligotrophic Balearic Basin, was analysed. Based on a first sampling (beam trawls, plankton nets and stomach contents), and a faunal reconstruction from a sediment core (MC2, at 1151 m), the supra(epi)benthic crustaceans at the VS summit (to 1300 m) were composed of nine Eucarida and 25 Peracarida. Polycheles typhlops, Munida tenuimana, and Aristeus antennatus were the dominant species among eucarids. Among Peracarida the most abundant species were the Mysida Boreomysis arctica, the Amphipoda Rhachtropis caeca, and the Isopoda Munnopsurus atlanticus. Among Decapoda, a species with a wide amplitude in their depth distribution and small eggs (i.e., with planktotrophic larvae), showed a higher colonisation capacity. In the absence of larvae, the colonisation of peracarids depends on the amplitude of their depth distribution and only those species that reach the highest depths in the entire Balearic Basin, at least 1600–1800 m, were able to colonise the summit of VS. The natatory capacity of the species also has some influence and whole groups with low natatory capacity, such as the Desmosomatidae, were completely absent on the VS summit; however, they are distributed throughout the Balearic Basin to depths (up to about 1500 m) exceeding the depth of the seamount summit. Therefore, colonisation by peracarids must not have occurred by swimming through the entire water column, but by swimming along or just above the bottom. Remains of some suprabenthic species (mainly the isopod M. atlanticus) in MC2 and another core collected in NW Mallorca (MC3, 1114 m), i.e., out of the VS, showed how isopod diversity and size distribution changed historically. Also, after the 1960s, a decrease in primary production due to a decrease in rainfall and river runoff associated with river damming could have reduced the abundance of M. atlanticus. These types of historical studies can be useful in interpreting long-term changes in deep-sea communities and optimising the management of these vulnerable areas.

Deepdive: Leveraging Pre-trained Deep Learning for Deep-Sea ROV Biota Identification in the Great Barrier Reef

Understanding and preserving the deep sea ecosystems is paramount for marine conservation efforts. Automated object (deep-sea biota) classification can enable the creation of detailed habitat maps that not only aid in biodiversity assessments but also provide essential data to evaluate ecosystem health and resilience. Having a significant source of labelled data helps prevent overfitting and enables training deep learning models with numerous parameters. In this paper, we contribute to the establishment of a significant deep-sea remotely operated vehicle (ROV) image classification dataset with 3994 images featuring deep-sea biota belonging to 33 classes. We manually label the images through rigorous quality control with human-in-the-loop image labelling. Leveraging data from ROV equipped with advanced imaging systems, our study provides results using novel deep-learning models for image classification. We use deep learning models including ResNet, DenseNet, Inception, and Inception-ResNet to benchmark the dataset that features class imbalance with many classes. Our results show that the Inception-ResNet model provides a mean classification accuracy of 65%, with AUC scores exceeding 0.8 for each class.

Into the deep: Exploring the molecular mechanisms of hyperactive behaviour induced by three rare earth elements in early life-stages of the deep-sea scavenging amphipod Tmetonyx cicada (Lysianassidae)

With increasing socio-economic importance of the rare earth elements and yttrium (REY), Norway has laid out plans for REY mining, from land-based to deep-sea mining, thereby enhancing REY mobility in the marine ecosystem. Little is known about associated environmental consequences, especially in the deep ocean. We explored the toxicity and modes of action of a light (Nd), medium (Gd) and heavy (Yb) REY-Cl3 at four concentrations (3, 30, 300, and 3000 μg L−1) in the Arcto-boreal deep-sea amphipod Tmetonyx cicada. At the highest concentration, REY solubility was limited and increased with atomic weight (Nd < Gd < Yb). Lethal effects were practically restricted to this treatment, with the lighter elements being more acutely toxic than Yb (from ∼50 % mortality in the Gd-group at dissolved 689–504 μg L−1 to <20 % in the Yb-group at ca. 2000 μg L−1), which could be a function of bioavailability. All three REY induced hyperactivity at the low-medium concentrations. Delving into the transcriptome of T. cicada allowed us to determine a whole array of potential (neurotoxic) mechanisms underlying this behaviour. Gd induced the vastest response, affecting serotonin-synthesis; sphingolipid-synthesis; the renin-angiotensin system; mitochondrial and endoplasmic reticulum functioning (Gd, Nd); and lysosome integrity (Gd, Yb); as well as the expression of hemocyanin, potentially governing REY-uptake (Gd, Yb). While Nd and Yb shared only few pathways, suggesting a link between mode of action and atomic weight/radius, almost all discussed mechanisms imply the disruption of organismal Ca-homeostasis. Despite only fragmental genomic information available for crustaceans to date, our results provide novel insight into the toxicophysiology of REY in marine biota. The neurotoxic/behavioural effects in T. cicada at concentrations with potential environmental relevance warn about the possibility of bottom-up ecological consequences in mining exposed fjords and deep-sea ecosystems, calling for follow-up studies and regulatory measures prior to the onset of REY mining in Norway.

Transition metals in alkaline Lost City vent fluids are sufficient for early-life metabolisms

Despite the importance of alkaline seafloor hydrothermal vents in broadening our understanding of deep-sea hydrothermal ecosystems, little is known about the mobility and concentrations of micronutrient transition metals in these environments. Here, we present new analyses of micronutrient transition metal concentrations in vent fluids from the iconic Lost City Hydrothermal Field (LCHF) and report concentrations of Fe = 2.9–18.3 µmol/kg, Zn = 1.30–5.86 µmol/kg, Cu = 0.43–5.06 µmol/kg, Ni = 86.4–556 nmol/kg, Mn = 8.3–274 nmol/kg, V = 25.9–127 nmol/kg, Mo = 24–94 nmol/kg, Co = 8.0–135 nmol/kg, W = 4.8–16 nmol/kg, and Cd = 1.7–4.5 nmol/kg. We additionally present results of a hydrothermal lherzolite alteration experiment conducted at 300 °C, 500 bar. Transition metal concentrations and major chemical parameters of experimental reaction fluids are broadly similar to LCHF vent fluids, indicating that transition metal concentrations in LCHF vent fluids, and alkaline hydrothermal fluids more generally, reflect metal solubility controlled by underlying rock-buffered hydrothermal reactions.Concentrations of Ni and Mo are especially noteworthy because of their recognized importance for biological methanogenesis (Ni) and nitrogen fixation (Mo). When compared with known biological thresholds, our findings indicate that Ni concentrations in LCHF vent fluids are sufficient to support the robust methane-metabolizing microbial communities observed in the immediate vicinity of LCHF vents and suggest that Ni availability influences the spatial distribution of LCHF methanogens. Furthermore, our laboratory hydrothermal experiments demonstrate that Mo concentrations of similar magnitude to those observed in LCHF vent fluids (and also modern seawater) can be obtained by hydrothermal alteration of ultramafic rocks with Mo-free (Na, Ca) Cl aqueous solution. Thus, we conclude that alkaline hydrothermal fluids were likely similarly enriched in Mo prior to oxidation of the Earth’s atmosphere and ocean, providing localized Mo-rich geochemical environments capable of supporting Mo-dependent nitrogen fixation at currently recognized threshold concentrations.

Aequorivita flava sp. nov., isolated from deep-sea sediments.

Three Gram-stain-negative, aerobic, non-motile, chemoheterotrophic, short-rod-shaped bacteria, designated CDY1-MB1T, CDY2-MB3, and BDY3-MB2, were isolated from three marine sediment samples collected in the eastern Pacific Ocean. Phylogenetic analysis based on 16S rRNA gene sequences indicated that these strains were related to the genus Aequorivita and close to the type strain of Aequorivita vitellina F4716T (with similarities of 98.0-98.1%). Strain CDY1-MB1T can grow at 15-37 °C (optimum 30 °C) and in media with pH 6-9 (optimum, pH 7), and tolerate up to 10% (w/v) NaCl. The predominant cellular fatty acids of strain CDY1-MB1T were iso-C15 : 0 (20.7%) and iso-C17 : 0 3-OH (12.8%); the sole respiratory quinone was menaquinone 6; the major polar lipids were phosphatidylethanolamine, two unidentified aminolipids and two unidentified polar lipids. The digital DNA-DNA hybridization/average nucleotide identity values between strains CDY1-MB1T, CDY2-MB3, and BDY3-MB2 and A. vitellina F4716T were 24.7%/81.6-81.7%, thereby indicating that strain CDY1-MB1T should represent a novel species of the genus Aequorivita. The genomic DNA G+C contents were 37.6 % in all three strains. Genomic analysis showed the presence of genes related to nitrogen and sulphur cycling, as well as metal reduction. The genetic traits of these strains indicate their possible roles in nutrient cycling and detoxification processes, potentially shaping the deep-sea ecosystem's health and resilience. Based upon the consensus of phenotypic and genotypic analyses, strain CDY1-MB1T should be classified as a novel species of the genus Aequorivita, for which the name Aequorivita flava sp. nov. is proposed. The type strain is CDY1-MB1T (=MCCC 1A16935T=KCTC 102223T).

Vertical structure of Caribbean deep-reef fishes from the altiphotic to deep-sea boundary

While recent technical breakthroughs have enabled advances in the description of reefs down to 150 m, the structure and depth zonation of deep-reef communities below 150 m remains largely unknown. Here, we present results from over 10 years of deep-reef fish surveys using human-occupied submersibles at four locations across the Caribbean Sea, constituting one of the only continuous reef-fish surveys from 10 to 480 m (1 site) and 40 to 300 m (3 sites). We identify four vertically stratified deep-reef fish communities between 40 and 300 m bordered by an altiphotic (0–10 m) and a deep-sea (300–480 m) community. We found a strong faunal break around 150 m that separates mesophotic and rariphotic zones and secondary breaks at ~ 70 to 90 m and ~ 180 to 200 m subdividing these zones into upper and lower communities. From 300 to 480 m in Roatán, we found a single fish community dominated by deep-sea families, indicating that the lower boundary of the reef-fish realm occurs at 300 m. No differences were found between communities ranging from 20 to 60 m, suggesting that fishes from the lower altiphotic and upper mesophotic form an ecological continuum. While some variability was observed across sites, the overall depth zonation and key species characterizing depth zones were consistent. Most deep-reef species observed were depth specialists restricted to a single depth zone, but many shallow-reef species extended down to mesophotic depths. Depth segregation among species of a genus was found across ten reef-fish genera and likely constitutes one of the mechanisms driving community distinctiveness and thereby fish diversity across depths.