Search Results (19)

Ti-6Al-4V titanium alloy is extensively employed in deep-sea structural applications owing to its excellent corrosion resistance, while its extra-low-interstitial (ELI) variant provides higher fracture toughness and is commonly presumed to exhibit even better stress corrosion cracking (SCC) resistance. In this work, displacement-rate-dependent fracture toughness (K_Q) measurements and failure analysis were performed for compact tension specimens machined from an engineering Ti-6Al-4V ELI plate with different orientations, tested in air and 3.5 wt.% NaCl solution over displacement rates of 0.0012–1.2 mm/min. In air, K_Q exhibits a pronounced loading-rate dependence, decreasing by more than 20% at low displacement rates relative to maximum rate, accompanied by quasi-cleavage features on the fracture surfaces indicative of hydrogen-assisted damage, likely arising from environmental or processing-related hydrogen uptake. In 3.5 wt.% NaCl solution, the minimum K_Q within the low-rate regime (0.0012–0.12 mm/min) is 58 MPa·m^0.5, comparable to values reported for conventional Ti-6Al-4V under similar conditions. The pronounced rate dependence and transition toward cleavage-like fracture reveal a strong coupling between loading kinetics and environmental degradation. This work demonstrates that enhanced intrinsic toughness does not necessarily translate into superior SCC resistance and establishes loading rate as a critical factor governing the environmental fracture of Ti-6Al-4V ELI under marine conditions. Full article

Xiaochikan Village, located in Guangdong Province in South China, is one of the few remaining traditional rammed earth dwellings of the Cantonese ethnic group in the Lingnan region. However, the influence of Zhuhai’s subtropical maritime monsoon climate has led to continuous physical and chemical erosion of the rammed earth walls. For example, cracking occurs due to high temperatures and heavy rain, accelerated weathering occurs due to salt spray deposition, and biological erosion occurs due to high humidity and high temperatures. Therefore, two experimental analysis techniques, X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), were used to explore the structural anti-erosion mechanism of the ancient, rammed earth buildings in Xiaochikan Village. The results show that (1) the morphological characteristics of the east and west walls of the rammed earth dwellings in Xiaochikan Village are more similar. The particles on the east wall are regular spherical or polygonal, small, and evenly distributed, while the particles on the west wall are mainly spherical and elliptical, with consistent size and less agglomeration. The surfaces of the particles on both walls are relatively smooth and flat. (2) The core element bases of the four wall samples are consistent, with C, Si, Al, Ca, and Fe as the core, accounting for more than 93%, reflecting the base characteristics of the local alluvial soil “silicate skeleton–carbonate cementation–organic matter residue” and reflecting the “local material” attribute of rammed earth. Except for the south wall sample, the Cl content of the remaining samples exceeds 1%. In the thermal map, Cl shows “pore/interstitial enrichment”, which confirms that the salinization process of marine aerosols with rainwater infiltration and evaporation residue is a common influence of marine climate. (3) The rammed earth walls in Xiaochikan Village consist of three main minerals: Quartz (SiO₂, including alpha-type SiO₂), Calcite (CaCO₃, including synthetic calcite), and Gibbsite (Al(OH)₃). Full article

The Kemp’s ridley sea turtle (Lepidochelys kempii) is the most critically endangered sea turtle species, with a distribution primarily restricted to the Gulf of Mexico. Its occurrence along the Iberian Peninsula is exceedingly rare. This study describes the postmortem findings of a juvenile L. kempii rescued off the Portuguese coast in 2024, which died after 11 days in rehabilitation despite intensive supportive care. Necropsy revealed severe, diffuse pneumonia. Histopathological examination showed interstitial inflammation and branching septate hyphae, while fungal culture and DNA sequencing confirmed the presence of Beauveria bassiana. Mycotic diseases in reptiles are often underrecognised but can lead to significant morbidity and mortality, particularly in immunocompromised or stressed individuals such as stranded marine turtles. This rare occurrence of a L. kempii on the Portuguese coast provides important insights into the species’ dispersal patterns and underlines the potential conservation implications of opportunistic fungal infections in endangered species. Full article

Titanium alloys are of significant value in aerospace, biomedical, and marine engineering applications due to their excellent specific strength and favorable biocompatibility. As a crucial interstitial solute, oxygen significantly influences the mechanical properties of titanium alloys. However, excessive oxygen content can lead to severe embrittlement and a significant reduction in ductility. This paper systematically reviews the mechanisms of microstructural evolution induced by oxygen in conventionally manufactured titanium alloys and their impact on mechanical properties, highlighting that conventional processes require complex post-treatments (PT) to achieve a balance between strength and plasticity. This assessment further explores the regulatory mechanisms of oxygen on the microstructure and mechanical properties of laser additive manufactured (LAM) titanium alloys, elucidating the fundamental phenomena regarding the oxygen–microstructure–property relationship. Finally, based on the current research progress, this paper provides an outlook on the future development directions and key research priorities in this field. This review offers valuable insights into the role of oxygen in titanium alloys and the development of high-performance titanium alloys. Full article

Freshwater slugs are scarce and belong exclusively to panpulmonate Acochlidimorpha. There is a radiation of eight species of large-sized slugs living benthically in rivers on tropical Indo-Pacific Islands. In the Western Atlantic, only one small interstitial slug, Tantulum elegans Rankin, 1979, is known from the Caribbean island of St. Vincent. We recently discovered a novel species of freshwater slugs in Cuba. Here, we describe Potamohedyle espinosai n. gen. n. sp., which is the first freshwater slug in the region of the Western Atlantic with a benthic lifestyle, in 3D-microanatomical and histological detail using light and scanning electron microscopy. It shows a mix of characters from different freshwater acochlidimorph genera, such as a medium body size, the presence of an osphradial ganglion, a distal gonoduct with a muscular sphincter, a penis with a solid thorn and cuticular comb, and a basal finger with a hollow stylet. Morphological adaptations to a life in freshwater include multiplicated renopericardioducts. The taxonomic character mix justifies the establishment of a novel genus within the herein diagnostically modified freshwater family Tantulidae. A molecular phylogenetic hypothesis of riverine slugs including the first Caribbean representatives suggests that the transition to freshwater occurred once along the stemline of limnic Acochlidiidae, secondarily marine Pseudunelidae and limnic Tantulidae. Full article

Human influence on Antarctic marine ecosystems is a growing concern, despite limited information being available. This study investigated the coastal meiofauna and environmental parameters of 10 locations, 4 of which served as reference points (OB1, OB2, OB3, and McGrady) and 6 which were impacted by different levels of human activity in the past and present (Wharf, Wilkes, BBIN, BBMID, BBOUT, and Shannon) in East Antarctica. Environmental variables such as metals, total petroleum hydrocarbons (TPHs), polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), grain size, organic matter content, and nutrients were measured for analysis. Locations close to human activities showed higher concentrations of pollutants (metals, TPHs, PBDEs, PCBs) and greater variations in meiofauna diversity compared to the reference sites (OB1, OB2, OB3, and McGrady). In the area impacted by the Casey Station waste dump (Brown Bay), the meiofauna community at the location furthest from the pollution (BBOUT) source exhibited greater diversity compared to the closest location (BBIN). In addition to metals and TPHs, particle size was also correlated with community patterns, with finer sediments associated with more impacted sites, facilitating the accumulation of toxic compounds. These results contribute to the understanding of the role and impact of pollutants on meiofauna biodiversity in Antarctic coastal ecosystems. Full article

Some, probably most and perhaps all, members of the phylum Nemertea are poisonous, documented so far from marine and benthic specimens. Although the toxicity of these animals has been long known, systematic studies on the characterization of toxins, mechanisms of toxicity, and toxin evolution for this group are scarce. Here, we present the first investigation of the molecular evolution of toxins in Nemertea. Using a proteo-transcriptomic approach, we described toxins in the body and poisonous mucus of the pilidiophoran Lineus sanguineus and the hoplonemertean Nemertopsis pamelaroeae. Using these new and publicly available transcriptomes, we investigated the molecular evolution of six selected toxin gene families. In addition, we also characterized in silico the toxin genes found in the interstitial hoplonemertean, Ototyphlonemertes erneba, a meiofaunal taxa. We successfully identified over 200 toxin transcripts in each of these species. Evidence of positive selection and gene duplication was observed in all investigated toxin genes. We hypothesized that the increased rates of gene duplications observed for Pilidiophora could be involved with the expansion of toxin genes. Studies concerning the natural history of Nemertea are still needed to understand the evolution of their toxins. Nevertheless, our results show evolutionary mechanisms similar to other venomous groups. Full article

(1) Background: An estuary is a zone in which sea and river waters mix. It is a specific area with a very non-stable environment and salinity gradient. However, little is known about the diversity of ciliate communities in estuarine benthic ecosystems in the Arctic. The aim of this paper is to describe the diversity of intertidal ciliates in the Chernaya river estuary (Kandalaksha Gulf, White Sea), which is characterized by a pronounced salinity gradient (0–22‰), on the basis of a recently published dataset. (2) Methods: We conducted our own investigations during the summer periods of 1998–2000. Material was collected at five permanent stations along the salinity gradient (0–22%) of the estuary. For each observation, the coordinates of the sampling sites, the number of individuals observed and the sampling date were recorded. The total effort comprised 35 sampling days, with five sampling sites at each date. (3) Results: The dataset contains 4270 unique occurrences of 119 ciliates taxa (109 species, 8 unidentified species of the genus level and 2 unidentified species on the family level). The total number of specimens represented is 64,475. (4) Conclusions: The largest classes in terms of species diversity are Hypotrichea (27 species), Gymnostomatea (26 species), Oligohymenophorea (17 species) and Karyorelictea (16 species). Full article

The temporal distribution of trace elements in a sediment core (SK117/GC-08) indicates minor changes in oxygenation during the last 100 kilo years in the bottom waters of the deeper eastern Arabian Sea. The high values of Mn, Co, Cu, Mn/Al, Co/Al, Cu/Al, V/Cr, and V/(V + Ni) in the sediments during interglacials and interstitials collectively indicate oxic conditions during warm periods. The high values of Cr, Ni, V, Mo, Cr/Al, Ni/Al, and Ni/Co in sediments during glacials and stadials collectively indicate dysoxic to suboxic conditions during the colder last glacial maximum and during the entire marine isotope stage two. The bottom waters have never experienced anoxic conditions. Multivariate statistics showed the attribution of the trace elements in two factors: cluster 1 (Co, Cu, Mn) was enriched during oxic conditions and cluster 2 (Cr, Mo, Ni, V) was enriched during dysoxic to suboxic conditions. Oxygenation conditions are mainly driven by variations in monsoon-controlled surface water productivity and changes in the flux of circumpolar deep water. The dysoxic to suboxic bottom water conditions developed at the core location during colder climates are very well synchronised with an increased organic matter flux. The main factor that controls the accumulation of the organic-rich sediments in the eastern Arabian Sea during a glacial is the increase in the supply of organic matter from increased primary productivity in the surface waters, controlled by winter monsoon winds, and localized convective mixing. During warmer interglacials and interstadials, the core location has remained well ventilated. Full article

Pyrites are widely distributed in marine sediments, the morphology of which is applied as a proxy to infer the redox conditions of bottom water, and identify diagenetic stages and hydrocarbon leakage activities. In this review, the methods used for the morphological study of pyrite are summarized. The textural and size characteristics of euhedral pyrite and pyrite aggregates, as the formation and evolution mechanism of pyrite are discussed for their significance in reconstructing the geochemical environment. The morphological study of pyrite includes shape observation, size estimation, and surface feature analysis. Scanning electron microscope and optical microscope are the main methods for morphological observation; transmission electron microscope and scanning tunneling microscope are applicable to observe nanoscale morphological structures and crystal growth on the crystal surface, and X-ray computed tomography is capable of measuring pyrite size distribution at the scale of a micrometer. Under the marine sedimentary condition, the single crystal of pyrite appears in cube, octahedron, dodecahedron, and their intermediates, the size of which ranges from several nanometers to more than 100 µm. The morphology of euhedral pyrite is controlled by temperature, pH, the chemical composition of interstitial water, etc., and might have been experienced in later reformation processes. The pyrite aggregates occur as framboid, rod-like, fossil-infilling, etc., characterized by the comparatively large size of several microns to several millimeters. It is found that certain textures correspond with different formation mechanisms and geochemical environments. Particularly, under special geological conditions, for instance, the methane leakage and/or decomposition of gas hydrate, pyrite is anomaly enriched with morphological textures of massive framboid cluster, rod-like aggregates, etc., and framboid is found with a large mean diameter (>20 µm) and standard deviation (>10 µm). These typical features can be employed to ascertain the position of the paleo sulfate methane transition zone (SMTZ). Full article

Cardiovascular diseases such as atherosclerosis and aortic valve sclerosis involve inflammatory reactions triggered by various stimuli, causing increased oxidative stress. This increased oxidative stress causes damage to the heart cells, with subsequent cell apoptosis or calcification. Currently, heart valve damage or heart valve diseases are treated by drugs or surgery. Natural antioxidant products are being investigated in related research, such as fucoxanthin (Fx), which is a marine carotenoid extracted from seaweed, with strong antioxidant, anti-inflammatory, and anti-tumor properties. This study aimed to explore the protective effect of Fx on heart valves under high oxidative stress, as well as the underlying mechanism of action. Rat heart valve interstitial cells under H₂O₂-induced oxidative stress were treated with Fx. Fx improved cell survival and reduced oxidative stress-induced DNA damage, which was assessed by cell viability analysis and staining with propidium iodide. Alizarin Red-S analysis indicated that Fx has a protective effect against calcification. Furthermore, Western blotting revealed that Fx abrogates oxidative stress-induced apoptosis via reducing the expression of apoptosis-related proteins as well as modulate Akt/ERK-related protein expression. Notably, in vivo experiments using 26 dogs treated with 60 mg/kg of Fx in combination with medical treatment for 0.5 to 2 years showed significant recovery in their echocardiographic parameters. Collectively, these in vitro and in vivo results highlight the potential of Fx to protect heart valve cells from high oxidative stress-induced damage. Full article

Cryptic species are a biological phenomenon only recently recognized due to progress in molecular studies. They pose a significant challenge to conventional taxonomic work since these species manifest low morphological differences, but considerable genetic disparity. New taxonomic methods are in development but have yet to be tested for many animal groups. Isopods belonging to the suborder Microcerberidea are one such group. The Asian microcerberid isopod, Coxicerberus fukudai (Ito, 1974), is a major component of marine interstitial fauna with suspected cryptic species inhabiting Japan and Korea. We chose six Korean populations with high molecular interpopulations divergence and applied 2D landmark-based geometric morphometrics to cephalic sensilla, pleonal points, and male pleopod II. This quantitative approach allowed us to study interpopulation size and shape variations, morphospace structure, and whether the morphological pattern mirrored the genetic species. We determined that a high degree of interpopulation size variation significantly influences shape changes. Once we removed the allometric effect, the size-corrected male pleopod II shape variations yielded a new species, C. jangsaensis sp. nov. At the same time, we were able to resolve the C. fukadai species complex. Full article

Members of the following marine annelid families are found almost exclusively in the interstitial environment and are highly adapted to move between sand grains, relying mostly on ciliary locomotion: Apharyngtidae n. fam., Dinophilidae, Diurodrilidae, Nerillidae, Lobatocerebridae, Parergodrilidae, Polygordiidae, Protodrilidae, Protodriloididae, Psammodrilidae and Saccocirridae. This article provides a review of the evolution, systematics, and diversity of these families, with the exception of Parergodrilidae, which was detailed in the review of Orbiniida by Meca, Zhadan, and Struck within this Special Issue. While several of the discussed families have previously only been known by a few described species, recent surveys inclusive of molecular approaches have increased the number of species, showing that all of the aforementioned families exhibit a high degree of cryptic diversity shadowed by a limited number of recognizable morphological traits. This is a challenge for studies of the evolution, taxonomy, and diversity of interstitial families as well as for their identification and incorporation into ecological surveys. By compiling a comprehensive and updated review on these interstitial families, we hope to promote new studies on their intriguing evolutionary histories, adapted life forms and high and hidden diversity. Full article

Sandy beaches represent two-thirds of littoral zones worldwide. Complex factors such as winds, waves, and sediment characterize this environment. Ciliophora is one of the most diversified unicellular eukaryotic phyla and, in marine sediments, can reach 40 species per cm³. Despite its importance, knowledge about interstitial communities is still lacking. In the present work, we characterized the assemblage of interstitial ciliates from sandy beaches in the north coastal area of Rio Grande do Sul state, southern Brazil. Fourteen sampling sites distributed along the swash zone of seven beaches with different degrees of urban development were sampled over the course of one year. At each site, eight sediment samples were taken, and a total of 51 species distributed in 37 ciliate genera were identified. Classes Spirotrichea (29%) and Karyorelictea (21%) accounted for 50% of ciliate species richness, with the highest richness being observed within the context of an intermediately urbanized setting. Community analyses revealed that ciliate community is influenced by urbanization degree and season, with distinct assemblages occurring in highly urbanized areas. In beaches affected by a high level of human activity, disturbance effects increased diversity, while in areas showing a milder influence of urbanization, the level of disturbance may be low, resulting in lower richness. Full article

Sub-seafloor microbial environments exhibit large carbon-isotope fractionation effects as a result of microbial enzymatic reactions. Isotopically light, dissolved inorganic carbon (DIC) derived from organic carbon is commonly released into the interstitial water due to microbial dissimilatory processes prevailing in the sub-surface biosphere. Much stronger carbon-isotope fractionation occurs, however, during methanogenesis, whereby methane is depleted in ¹³C and, by mass balance, DIC is enriched in ¹³C, such that isotopic distributions are predominantly influenced by microbial metabolisms involving methane. Methane metabolisms are essentially mediated through a single enzymatic pathway in both Archaea and Bacteria, the Wood–Ljungdahl (WL) pathway, but it remains unclear where in the pathway carbon-isotope fractionation occurs. While it is generally assumed that fractionation arises from kinetic effects of enzymatic reactions, it has recently been suggested that partial carbon-isotope equilibration occurs within the pathway of anaerobic methane oxidation. Equilibrium fractionation might also occur during methanogenesis, as the isotopic difference between DIC and methane is commonly on the order of 75‰, which is near the thermodynamic equilibrium. The isotopic signature in DIC and methane highly varies in marine porewaters, reflecting the distribution of different microbial metabolisms contributing to DIC. If carbon isotopes are preserved in diagenetic carbonates, they may provide a powerful biosignature for the conditions in the deep biosphere, specifically in proximity to the sulphate–methane transition zone. Large variations in isotopic signatures in diagenetic archives have been found that document dramatic changes in sub-seafloor biosphere activity over geological time scales. We present a brief overview on carbon isotopes, including microbial fractionation mechanisms, transport effects, preservation in diagenetic carbonate archives, and their implications for the past sub-seafloor biosphere and its role in the global carbon cycle. We discuss open questions and future potentials of carbon isotopes as archives to trace the deep biosphere through time. Full article