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Volume 39 ， Issue 5 ， 2021
Preface
- Abstract：Massive seamounts have been surveyed and documented in the last decades. However, the morphologies of seamounts are usually described in qualitative manners, yet few quantitative detections have been carried out. Here, based on the high-resolution multi-beam bathymetric data, we report a recentlysurveyed guyot on the Caroline Ridge in the West Pacific, and the large-scale volcanic structures and smallscale erosive-depositional landforms in the guyot area have been identified. The multifractal features of the guyot are characterized for the first time by applying multifractal detrended fluctuation analysis on the surveyed bathymetric data. The results indicate that the multifractal spectrum parameters of the seafloor have strong spatial dependency on the fluctuations of local landforms. Both small- and large-scale components contribute to the degree of asymmetry of the multifractal spectrum (B), while the fluctuations of B are mostly attributed to the changes in small-scale roughness. The maximum singularity strength (α0 correlates well with the roughness of large-scale landforms and likely reflects the large-scale topographic irregularity. Comparing to traditional roughness parameters or monofractal exponents, multifractal spectra are able to depict not only the multiscale characteristics of submarine landforms, but also the spatial variations of scaling behaviors. Although more comparative works are required for various seamounts, we hope this study, as a case of quantifying geomorphological characters and multiscale behaviors of seamounts, can encourage further studies on seamounts concerning geomorphological processes, ocean bottom circulations, and seamount ecosystems.Keywords：guyot;morphology;multifractal detrended fluctuation analysis (MFDFA);Caroline Ridge;West Pacific Ocean5|0|3Updated：2023-04-27
- Abstract：Ferromanganese crusts (Fe-Mn crusts) grow very slow and can be treated as condensed stratigraphic sections recording paleo-oceanographic environmental information and local key geological events during the mineralization process. Geochronology, textures, mineralogy, and geochemistry of a Fe-Mn crust sample from the CM6 Seamount of the Caroline Ridge in the Western Pacific Ocean were analyzed by means of electron probe microanalysis and X-ray diffraction. The Fe-Mn crust shows three layers in textural characteristics from bottom to top. The lower, middle, and upper layers presence mottled, botryoidal, and columnar textures, respectively. Ferruginous vernadite, Fe hydroxide, amorphous silicate minerals, calcite, quartz, and feldspar are the main minerals of the Fe-Mn crust. Using cobalt chronometry method, the cumulative growth time of the Fe-Mn crust was determined to be 11 Ma or 25 Ma, of which 25 Ma is inconsistent with other lines of age constraint brought by dating of the substrate. The co-existence of abundant silicate minerals and bioclasts in the middle and lower layers of the Fe-Mn crust diluted the ferromanganese oxide deposits, thus affected the texture, minerals, and geochemical characteristics of the Fe-Mn crust. Variations in Mn, Co, Ni, and other elements content and the burial of opal-A recorded the expansion of oxygen minimum zone (OMZ) in the upper layer of the Fe-Mn crust. In addition, the highreflectivity Fe-rich laminae might indicate the surrounding volcanic activity. The Fe-Mn crust sample was determined to be hydrogenic by electron probe micro-analyzer (EPMA). The findings help us understand the geochemical characteristics of the Fe-Mn crust in the Caroline Ridge Seamount in the Western Pacific and the variations of paleo-oceanographic environment clues borne by the Fe-Mn crusts.Keywords：ferromanganese crust;geochemistry;geological significance;environment influence;seamount5|0|1Updated：2023-04-27
- Abstract：The ocean is an important inventory of anthropogenic mercury (Hg), yet the history of anthropogenic Hg accumulation in the ocean remains largely unexplored. Deep-sea corals are an emerging archive of past ocean chemistry, which take in sinking or suspended particulate organic matter as their food sources. Such organic matter would exchange Hg with the local seawater before being consumed by the deepsea corals. As such, the organics preserved in the coral skeleton may record the Hg evolution of the ambient seawater during the time of coral growth. Here, we report the first data on Hg concentrations variability of a deep-sea proteinaceous coral in the oligotrophic North Pacific at the water depth of 1 249 m, in attempt to understand the transfer of anthropogenic Hg into the deep Pacific ocean over the last seven centuries. We find that the Hg concentrations of different coral growth layers have remained relatively constant albeit with considerable short-term variability through time. The overall stable Hg concentration of the last seven centuries recorded in our sample suggests that anthropogenic pollution is not yet a clearly resolvable component in the deep oligotrophic North Pacific waters, in agreement with recent estimation from modelling works and observational studies of modern seawater profiles. As there is hardly an unambiguous way to separate anthropogenic Hg from the natural background based on recent seawater profiles, our historical data provide valuable information helping to understand the oceanic cycle of Hg through time.Keywords：deep-sea coral;mercury;deep water;particulate organic matter;anthropogenic perturbation4|0|1Updated：2023-04-27
Seamount geological and geochemical characteristics
- Abstract：Physical oceanography plays an important role in the formation of submarine sediments, and the distribution of nutriments and biocenoses in seamounts. The M4 seamount is located in the Caroline Island Ridge of the Western Pacific Ocean. The physical properties around M4 seamount are preliminarily analyzed based on the in-situ data obtained in summer 2017 in Caroline M4 seamount and open-sourced data. We found that the water in the upper 200 m is controlled by the westward North Equatorial Current (NEC), while the water between 300-1 000 m is dominated by the eastward North Equatorial Undercurrent (NEUC). The current direction fluctuates significantly below 300 m at upstream stations. At the same depth of the lee sides, the current direction changes with the distance from seamount. These are likely caused by the obstacle of M4 seamount. The calculation results show that there is an anticyclonic cap above M4 seamount caused by tidal rectification. Tidal currents in M4 seamount are squeezed by the topography and amplified, and the amplified tidal currents play a dominant role in M4 seamount. First, the circulation system generated by the interaction of the amplified tidal current and M4 seamount drives the upward/downward movement of the isotherms. Secondly, the thickness of the surface turbulent layer is changed with the tidal phase. Thirdly, high turbulent diffusivities are found in the bottom of M4 seamount, and these are most likely attributed to the turbulent mixing induced by the mutual effect between semidiurnal tidal currents and steep bathymetry. This article of physical oceanography provides scientific basis for further analysis of the distribution of biological community and deposition mechanism in M4 seamount.Keywords：Caroline seamount;tropical Western Pacific Ocean;currents;water masses;tides;turbulent diffusivities4|0|4Updated：2023-04-27
- Abstract：As a serious consequence of ocean warming and increased stratification, a rapid decrease in dissolved oxygen (DO) content of the world's oceans has attracted more and more attention recently. In open oceans, the decline of DO is characterized by the expansion of oxygen minimum zones (OMZs) in the ocean interior. Vast OMZs exist within the mesopelagic zones of the Tropical Western Pacific (TWP), but have gained very little attention. In this study, we focus on characteristics of OMZs in three typical seamounts areas (named Y3, M2, and Kocebu, respectively) of the TWP. Based on distributions of DO, the OMZs of the three seamounts areas are very different in scope, thickness, and the minimum oxygen content. The significantly different characteristics of OMZs at the seamounts are mainly because they are located in regions affected by different ventilation and consumption characteristic. To quantitatively describe the intensity of OMZs, a parameter, IOMZ, is firstly proposed. According to this quantitative parameter, the intensity order of OMZs for the three seamounts areas is Kocebu>M2>Y3. Potential biogeochemical effects of OMZs in the three seamounts areas are discussed using IOMZ. With higher IOMZ, the degradation of particulate organic carbon (POC) tends to be lower. Yet because of the limited data, their relationship still need more research to prove. However, if this relationship holds in global oceans, the presence of seamounts would-under climate warming with expanding OMZs-promote vertical transport of POC resulting in an enhanced biological pump. Our study provides a new way to quantitatively study the impact of OMZs on the efficiency of biological pump.Keywords：oxygen minimum zone (OMZ);particulate organic carbon (POC);biogeochemical effect;seamount;Western Pacific4|0|0Updated：2023-04-27
- Abstract：Comprehensive surveys were conducted in the Kocebu deep seamount and the M4 shallow seamount in the Western Pacific Ocean in March 2018 and May 2019, respectively. The distributions of nutrients in euphotic zone of the two seamount-areas were revealed, and the causative controlling factors were analyzed. Results show that the vertical distribution of nutrients in the two seamount-areas accorded with the general law of the oligotrophic ocean. The concentrations of NO3-N, PO4-P, and SiO3-Si generally increased gradually with the increase of water depth, and they were extremely low in water layers within 100 m. The area of high NO2-N concentration well agreed with the Deep Chlorophyll Maximum Layer. On the other hand, the distribution of water masses and phytoplankton and hydrological conditions in the two seamount-areas were different, resulting in lower concentrations of NO3-N, PO4-P, and SiO3-Si in the water layers below 100 m in the Kocebu seamount area than those in the M4 seamount area. In addition, NO2-N was affected by the distribution of phytoplankton, and distributed mainly in the water layers of 150 and 100 m. There was upwelling in the euphotic zone of M4 seamount area, causing accumulations of nutrients and phytoplankton around the seamount, forming a "seamount effect"; however, no such an effect was found in Kocebu seamount area. Affected by the composition of biological community and the "seamount effect", the nitrogen limitation in the M4 seamount area was not significant, and the dissolved inorganic nitrogen (DIN): PO4-P and SiO3-Si: DIN were closer to the Redfield ratios.Keywords：nutrients;comparison;seamount;Western Pacific Ocean4|3|1Updated：2023-04-27
- Abstract：The climate variability induced by the El Niño-Southern Oscillation (ENSO) cycle drives significant changes in the physical state of the tropical Western Pacific, which has important impacts on the upper ocean carbon cycle. During 2015-2016, a super El Niño event occurred in the equatorial Pacific. Suspended particulate matter (SPM) data and related environmental observations in the tropical Western Pacific were obtained during two cruises in Dec. 2014 and 2015, which coincided with the early and peak stages of this super El Niño event. Compared with the marine environments in the tropical Western Pacific in Dec. 2014, an obviously enhanced upwelling occurred in the Mindanao Dome region; the nitrate concentration in the euphotic zone almost tripled; and the size, mass concentration, and volume concentration of SPM obviously increased in Dec. 2015. The enhanced upwelling in the Mindanao Dome region carried cold but eutrophic water upward from the deep ocean to shallow depths, even into the euphotic zone, which disrupted the previously N-limited conditions and induced a remarkable increase in phytoplankton blooms in the euphotic zone. These results reveal the mechanism of how nutrient-limited ecosystems in the tropical Western Pacific respond to super El Niño events. In the context of the ENSO cycle, if predicted changes in biogenic particles occur, the proportion of carbon storage in the tropical Western Pacific is estimated to be increased by more than 52%, ultimately affecting the regional and possibly even global carbon cycle. This paper highlights the prospect for long-term prediction of the impact of a super El Niño event on the global carbon cycle and has profound implications for understanding El Niño events.Keywords：suspended particulate matter;field observations;tropical Western Pacific;2015/2016 super El Niño event;ocean carbon cycle4|3|2Updated：2023-04-27
Seamount physicochemical environments
- Abstract：The oxygen minimum zones (OMZs) are globally expanding, yet the variation pattern of microbial communities related to dissolved oxygen levels remain unclear. Spatial variability of bacterial diversity and community composition (represented by 16S rRNA) of six stations was investigated within the water column in the seamount area of Tropical Western Pacific Ocean (TWPO) in May 2019. The seawater has dissolved oxygen (DO) concentration of 3.01-6.68 mg/L and the core of the oxygen minimum zones was located between the depths of 650 m and 1 750 m. The bacterial alpha-diversity showed unimodal pattern with the decreasing DO with depths and peaked in the upper oxycline (UO) of OMZs. The bacterial community structure of the mixed layer (ML) and the bottom layer clustered and separated from each other, while those of UO and the OMZ core (OM) clustered and overlapped. Overall, bacterial community composition transitioned from being Alphaproteobacteria and Gammaproteobacteria-dominant in ML to being Gammaproteobacteria and Nitrososphaeria/Deltaproteobacteria-dominant in UO and OM, and then changed to being Clostridia and unidentified_Actinobacteria-dominant in the bottom layer. Moreover, both bacterial alpha-diversity and the abundant classes fitted varying sectioned functions with DO. The DO solely explained 40.37% of the variation of bacterial community composition among layers (P < 0.001). The predicted function profiling showed that the water column was predominant by chemoheterotrophy, cyanobacteria, and photoautotrophy in ML, by chemoheterotrophy and nitrate/sulfide cycling in UO and OM, and by chemoheterotrophy and fermentation in the bottom layer. Our findings revealed the DO-associated variation in bacterial diversity and community composition, and help to clarify the potential responses of microbes and their involved biogeochemical processes to the expansion and intensification of OMZs.Keywords：bacterial diversity;community composition;oxygen minimum zones (OMZs);dissolved oxygen;Tropical Western Pacific Ocean (TWPO)4|0|1Updated：2023-04-27
- Abstract：Trait structure is increasingly used in plankton ecology to understand diversity and biogeography. However, our knowledge of microzooplankton (e.g. planktonic ciliates) trait structure and its variation with hydrography is limited. In this study, we analyzed planktonic ciliate trait structure in waters with different hydrography and deep Chlorophyll a maximum (DCM) layers over three seamounts: Yap, Mariana, and Caroline seamounts. Mariana seamount had a lower surface temperature than the Yap and Caroline seamounts. DCM layers over Mariana and Caroline seamounts were deeper than Yap seamount. There was a weak upwelling in upper 50 m around top of Mariana seamount. The ciliate distribution showed bimodal pattern (high abundance appeared in the surface and DCM layers) over three seamounts. At surface layer, the large size-fraction (>30 μm) abundance proportion to aloricate ciliate over Yap seamount (44.4%) was higher than Mariana (32.8%) and Caroline (36.1%) seamounts. For tintinnid abundance proportion to total ciliate, Mariana (12.0%) and Caroline (11.5%) seamounts at about 100-m depth were higher than that of Yap seamount (6.4%). Vertically, tintinnid could be divided into 4 groups over the three seamounts. At 30-m depth, group Ⅰ (species occurring from surface to 100 m only) was dominant component over Yap and Caroline seamounts, while group Ⅳ (species occurring at every depth) changed into dominant component over Mariana seamount, the weak upwelling might be the reason. Salpingella faurei was the top dominant species, which corresponded to deeper DCM layers over Mariana and Caroline seamounts. Our results showed that the upwelling and the deeper DCM could influence the planktonic ciliate trait structure.Keywords：planktonic ciliate;upwelling;seamount;vertical distribution;Western Pacific Ocean5|3|0Updated：2023-04-27
- Abstract：Seamount is a unique deep-sea ecosystem widely distributed in the world. Its biodiversity is vibrant due to its specific geographical and hydrological conditions. However, the diversity and features of foraminifera in such an environment have rarely been studied. We extracted environmental DNA (eDNA) in sediments and amplified the partial small subunit ribosomal DNA (SSU rDNA) of foraminifera to understand the foraminiferal diversity from four sites in Magellan Seamount (Western Pacific Ocean). Partial SSU rDNA sequencing was conducted and 912 979 foraminiferal reads were obtained and gathered into 266 operational taxonomic units (OTUs). In the available dataset, a high proportion of rare OTUs and low identity OTUs in each studied sample showed that the Magellan Seamount foraminiferal community might have a high genetic novelty. The relative abundance of foraminifera varied between replicates probably due to the existence of bias in amplification process and patchiness of the deep-sea floor. It showed that the Magellan Seamount has a relatively high benthic foraminiferal diversity characterized mainly by monothalamiids (76.37% of total reads) in association with rotaliids (19.03% of total reads), including planktic foraminiferal sequences (38.58% of rotaliids; 7.36% of total reads). The remaining reads were assigned to miliolids (0.83% of total reads) and textulariids (0.66% of total reads), and 3.11% of total reads are unassigned to a specific family. The comparative analysis with foraminiferal assemblages from coastal and deep-sea environments indicated that seamounts could aggregate species from a nearby deep-sea.Keywords：metabarcoding;Magellan Seamount;foraminifera;Western Pacific Ocean5|0|1Updated：2023-04-27
Seamount microbial diversity and ecology
- Abstract：A new species of Macandrewia Gray from a seamount near Yap Trench in the Western Pacific Ocean was described. Macandrewia yapensis sp. nov. is distinct from its congeners by possessing a foliate shape with contorted lamellae, tuberculiform terminations of desmas, and unique size of spicules. This is the third species of Macandrewia described from the Pacific Ocean. In addition, a partial sequence of COI gene was obtained from the new specimen and then it submitted to GenBank. Phylogenetic tree constructed with the partial COI sequences appears to exhibit a more congruent relationship with morphological data of macandrewiid species compared to 28S gene tree.Keywords：'Lithistid' demosponges;morphological and molecular analyses;new species;Macandrewia yapensis sp. nov4|0|1Updated：2023-04-27
- Abstract：Three deep-sea black corals belonging to the family Schizopathidae, are reported from two seamounts on the Caroline Ridge in the tropical Western Pacific: Umbellapathes parva sp. nov. with depth of 1 488-1 766 m, Telopathes cf. magna MacIsaac & Best, 2013 with depth of 937-1 016 m, and Stauropathes cf. punctata (Roule, 1905) with depth of 942-1 353 m. The latter two species are the first records in the Western Pacific Ocean. U. parva sp. nov. is characterized by monopodial corallum, relatively long unpinnulated stalk with complex pinnulated branches developing from the lowermost primary pinnules and small spines. It differs from two known congeners by much smaller spines and the present of secondary pinnules. T. cf. magna MacIsaac & Best, 2013 has sparsely branched corallum, relatively long and simple pinnules arranged in subopposite or alternate pairs. S. cf. punctata (Roule, 1905) is characterized by the corallum with almost planar pinnulated branches, and pinnules arranged in subopposite pairs. Our results indicate that the corallum size and shape are variable in conspecific specimens particularly those at different growth stages. By contrast, the size of the polypar spines as well as the abpolypar spines have little variation and can be served as a main differing feature for schizopathid species. The phylogenetic analyses using nuclear internal transcribed spacer region (spanning partial 18S rDNA, ITS1, 5.8S, ITS2, and partial 28S rDNA) and two mitochondrial fragments cox3-IGR-cox1 (COI) and trnW-IGR-nad2 (NAD2) showed Telopathes, Stauropathes, and Bathypathes had close relationships, and Umbellapathes formed a sister clade with Alternatipathes.Keywords：Anthozoa;black coral;new species;seamount;taxonomy;Western Pacific4|3|2Updated：2023-04-27
- Abstract：A new species of bubblegum coral, Paragorgia papillata sp. nov., discovered from a seamount located on the Caroline Ridge at the water depth of 858 m, is studied using morphological and molecular approaches. The new gorgonian is white-colored, uniplanar with prominent autozooids, and measures about 670-mm high and 690-mm wide. The genetic distance and phylogenetic analysis showed that P. papillata sp. nov. was closely related to P. coralloides Bayer, 1993, but the former differs morphologically from the latter by its prominent calyces (diameter 2.0-4.0 mm and height 1.5-3.0 mm vs. both diameter and height about 1 mm), white cortex (vs. pink), regular 8-radiates in surface cortex (vs. mostly 8-radiate derived globular radiates) and highly ornate medullar spindles (length 185-400 μm vs. no more than 150 μm). P. papillata sp. nov. is the third known white-colored species of the genus, and the fifth species found in the tropical Western Pacific.Keywords：Paragorgia;gorgonian;Scleraxonia;Cnidaria;new species;seamount4|0|2Updated：2023-04-27
- Abstract：Two new species of Chrysogorgia Duchassaing & Michelotti, 1864 collected from the Caroline seamounts in the tropical Western Pacific Ocean are described. Chrysogorgia pinniformis sp. nov. belongs to Versluys' group C (Squamosae typicae) with only scales in polyp body wall and tentacles. C. pinniformis sp. nov. is characterized by large branches pinnately branched and forming multiple fans with its small branches regularly and quasi-dichotomous branched, and scales and rods present in the polyp mouth area. It is most similar to C. pinnata Cairns, 2007 by the pinnate trait, but differs from the latter by its group C pattern (vs. group A, Spiculosae) and having sclerites present in the polyp mouth area (vs. absent). Chrysogorgia varians sp. nov. belongs to the Chrysogorgia group A (Spiculosae) with rods distributed in the polyp body wall and tentacles. It is characterized by warty rods and elongated scales in the tentacles, many warts and ridges on the scales, conspicuously toothed margins at the rounded ends in the pinnules, and small rods with ridge-like warts in the polyp mouth area. This species was frequent and abundant in the Caroline seamounts during our cruises and its morphological variability in growth period was obvious. The phylogenetic analyses based on mtMutS and 28S rDNA regions supported the assignment of the new species to the genus Chrysogorgia. However, the mtMutS marker showed very limited usefulness for species delimitation and inner relationship inference of Chrysogorgia. In contrast, the 28S rDNA showed much higher level of genetic variation, and it may be a potential barcode for this genus. In the 28S rDNA trees, the two new species clustered together. Additionally, compilation of our data showed that 42 of 78 (ca. 54%) Chrysogorgia species were found in the Indo-West Pacific convergent region, indicating that this area may be a hotspot of deep-water Chrysogorgia species.Keywords：Anthozoa;Octocorallia;Chrysogorgiidae;deep sea;taxonomy4|0|1Updated：2023-04-27
- Abstract：Sea pens are a highly specialized and morphologically distinct group of octocorallians, but many taxa were poorly described and their phylogenetic relationships are still poorly known. We describe two species of sea pens collected from the tropical Western Pacific: Alloptilella splendida gen. et sp. nov. and Scytalium veneris (Thomson & Henderson, 1906). Alloptilella splendida gen. et sp. nov. accords with the definition of the recently resurrected genus Ptilella Gray, 1870 in most characters, but differs from the latter in the arrangement of autozooids and the location of mesozooids. The new species mostly resembles Pennatula naresi Kölliker (1880), but differs by the location of mesozooids and the reddish color of sclerites surrounding siphonozooids. The generic separation is also well supported by their genetic distances and the molecular phylogenetic trees constructed by the concatenated mtMutS-COI-28S, where Alloptilella clustered with Scytalium Herklots, 1858 and formed a clade with the cluster of Ptilella and Distichoptilum. Scytalium veneris, usually considered as a junior synonym of Scytalium sarsii Herklots, 1858, is resurrected by recognizing their distinctive differences. This is the first record of Scytalium veneris outside its type locality, and the phylogenetic analysis indicates that Scytalium is a monophyletic group. Both the families Pennatulidae and Virgulariidae are polyphyletic, and more morphological and molecular data are needed to clarify the phylogenetic positions of pennatulacean families and genera.Keywords：sea pen;Pennatulidae;Alloptilella;new species;Scytalium;seamount4|0|1Updated：2023-04-27
Seamount megabenthos taxonomy and phylogeny
- Abstract：Laetmonice Kinberg, 1856 is a remarkable genus characterized by having harpoon notochaetae in the polychaete family Aphroditidae. We describe a new species of Laetmonice, Laetmonice iocasica sp. nov., found from seamounts on the Caroline Ridge in the tropical Western Pacific. The new species is readily distinguished from congeners, particularly those distributed in the Indo-Pacific Ocean by possessing 45 segments with 18 pairs of elytra, and the tuberculated harpoon notochaetae in the elytrigerous segments, which are replaced by tuberculated notochaetae without recurved fangs on segments 4 and 5. Laetmonice iocasica sp. nov. is closely related to L. producta Grube, 1877, but differs in both morphology and the genetic distance of the mitochondrial cytochrome oxidase subunit Ⅰ (COⅠ) sequences. Laetmonice producta Grube, 1877 contained five varieties reported in various marine areas, which have been raised to species level. However, the records of L. producta from the Sagami Bay and Suruga Bay in Japan and in the south-eastern Australia remain obscure and probably represent a different species. The data indicate that L. producta, which was originally described from Kerguelen Islands in the Southern Ocean and later commonly found on the Antarctic shelf, is probably distributed only at high latitudes of the Southern Hemisphere.Keywords：Polychaeta;taxonomy;biodiversity;deep-sea4|0|2Updated：2023-04-27
- Abstract：During an expedition to a seamount at Caroline Plate in the tropical Western Pacific, a new species of Tritonia was sampled from the upper bathyal zone at depth of 970-1 262 m. This new species, Tritonia iocasica sp. nov., represents the first tritoniid nudibranch known to feed on octocoral of the family Melithaeidae. The species is up to 120 mm in length, pinkish in color; with the rhinophoral sheath divided into several petaliform extensions; veil with about 18 elongate digitiform processes; notal margin with 17-19 pairs of secondary gills; anus located below the 5th and 6th secondary gills, and the genitalia below the 3rd secondary gill on the right side of the body. Based on these external features, T. iocasica sp. nov. can be clearly distinguished from all previously described members of the genus. Phylogenetic analyses of two mitochondrial (COI, 16S rRNA) and a nuclear (H3) genes using Bayesian inference, maximum likelihood, and species delimitation analysis also support the separation of T. iocasica sp. nov. from its congeners.Keywords：Tritoniidae;Mariana Trench;upper bathyal zone;Melithaeidae4|0|0Updated：2023-04-27
- Abstract：A new genus and species of axiid shrimp, Carolinaxius kexuae gen. et sp. nov. is described and illustrated based on a single specimen collected from an unnamed seamount in the Caroline Ridge, Northwest Pacific. Although both chelipeds are missing, the specimen can be distinguished from other axiid genera by a combination of characteristics: narrowly triangular rostrum; median carina and lateral gastric carina each with one prominent tooth; submedian gastric carinae converging posteriorly, with teeth; cornea weakly pigmented, eyestalk with acute distomesial tooth on dorsal surface; male pleopod 1 two-articled; pleopod 2 with appendix interna and appendix masculina; pleopods 3-5 with appendix interna. The molecular phylogeny suggests the new genus is most closely related to another recently described genus living inside hexactinellid sponges on seamounts in the Indian Ocean, Montanaxius Dworschak, 2016. However, it differs from Montanaxius in the shape of the rostrum, the arrangement of teeth on the carapace, and the shape of the eyestalk. Besides, the significant molecular differences support the two belonging to different genera.Keywords：Carolinaxius kexuae gen. et sp. nov.;taxonomy;molecular evidence;deep-sea;seamount4|0|1Updated：2023-04-27
- Abstract：The genus Munidopsis has high biodiversity in seamount habitats. In this study, two new Munidopsis species, Munidopsis ahyongi sp. nov. and Munidopsis carolinensis sp. nov. from the Caroline Ridge in the tropical western Pacific Ocean were described. M. ahyongi sp. nov. is very similar to a group of species in the M. serricornis complex, but can be readily distinguished from the related species in having the oblique posterior orbital margins, 2 spines on the lateral carapace margin, and a relatively longer rostral median spine. M. carolinensis sp. nov. is different from two related species primarily in having oblique frontal margins, blunt outer orbital angles, straight lateral margins of the rostrum, scale-like rugae on sternites 5-7, and less spinose pereopod 1 (chelipeds, P1) merus and carpus. Aside from the morphological comparisons, DNA barcode analysis and phylogenetic analysis based on the cytochrome c oxidase subunit I gene (COI) were employed for the identification of these new species.Keywords：Munidopsis;new species;seamount;tropical Western Pacific Ocean;DNA barcodes4|0|1Updated：2023-04-27
- Abstract：To reveal the tectonic characteristics of the continental margins in the southwest subbasin (SWB) of the South China Sea, a long high-resolution seismic profile was studied using empty basin subsidence. We find that tectonic subsidence features on both margins are uniformly divided into three stages: (1) slow subsidence from Tg to 18.5 Ma (synrift stage); (2) extremely slow subsidence/uplift from 18.5 to 16 Ma (spreading stage); and (3) accelerated subsidence from 16 to 0 Ma (post-spreading stage). This feature differs from the classic tectonic subsidence pattern of rifted basins, which exhibits fast subsidence during synrift stage and slow subsidence during the post-rift stage. The tectonic uplift occurred during the spreading stage and the magnitude increased from the continent to the ocean, which is likely related to mantle flow during seafloor spreading. We propose that lower crustal flow played a significant role in the tectonic evolution of the continental margins of the SWB. The lower crust of the SWB margins was warmer and therefore weaker, and more prone to flow beneath the faulting center, which compensated for the upper crustal thinning caused by brittle faulting during the synrift period and thus reduced the tectonic subsidence rate. During the spreading stage, faulting attenuated rapidly, and a necking zone appeared at the continentocean transition formed by lithospheric extension. With upwelling asthenosphere, small-scale secondary mantle convection occurred under the necking zone, which raised the continental margin isotherms and increased the buoyancy. Simultaneously, secondary mantle convection lifted the overriding crust, thus the overall subsidence rate decreased sharply or even reversed to uplift. After seafloor spreading, the effect of mantle convection faded away, and sediment loading drove the lower crust to flow landward. Thermal relaxation, lower crust flow, and vanish of secondary mantle convection together led to rapid subsidence in this stage.Keywords：tectonic subsidence;lower crustal flow;tectonic evolution;southwest subbasin;South China Sea6|0|2Updated：2023-04-27
- Abstract：To investigate the nature of gas hydrates in the Makran area, new high-resolution geophysical data were acquired between 2018-2019. The data collected comprise multibeam and two-dimensional multi-channel seismic reflection data. The multibeam bathymetry data show East-North-East (ENE) ridges, piggy-back basins, canyon and channel systems, and the morphology of the abyssal plain. Continuous and discontinuous bottom simulating reflectors (BSRs) occur in the piggy-back basins on most of the seismic profiles available. The BSRs cut the dipping layers with strong amplitude and reversed polarity. Discontinuous BSRs indicate a transition along a dipping high-permeable sand layers from gas-rich segment to the gas hydrate-bearing segment and suggest alternating sediments of fine and relatively coarse grain size. Double BSRs are highly dynamic and attributed to slumps occurring in the study area. The BSRs induced by slumps are located both at deep and shallow depths, responding to the temperature or pressure variation. For the first time, BSRs are observed in the abyssal plain of the Makran area, being associated with anticline structures, which do not show large spatial continuity and are strongly conditioned by structural conditions such as anticlines and fluid migration pathways, including deep fault, gas chimney, and high-permeable sedimentary layer. Our results may help to assess the gas hydrate potential within the piggy-back basins and to determine the most promising target areas. Moreover, results about the abyssal plain BSR may help to locate hydrocarbon reservoirs in the deep ocean.Keywords：gas hydrate-bearing sand-prone sediments;double bottom simulating reflector (BSR);multiple BSR;canyon channel system;abyssal plain4|0|3Updated：2023-04-27
Geology
- Abstract：Stable Pb isotopes in surface and core sediments were determined to identify the sources of Pb contaminants in the northern East China Sea (ECS). The Bayesian stable isotope mixing model was used to quantify the contributions of Pb sources. The results show that since the late 1980s, ratios of 207Pb/206Pb and 208Pb/206Pb increased in the top 34-cm sediment shown in the coastal core samples,reflecting elevated anthropogenic Pb input in coastal sea. Seaward increase of 207Pb/206Pb and 208Pb/206Pb ratios in surface sediments reveals that anthropogenic Pb came mainly via atmospheric transmission into the ECS. Anthropogenic sources accounted for 12.0%-21.1% of the total Pb in sediments after the 1990s. Coal combustion was the largest anthropogenic contributor (47.5%±18.8%),and Pb mining and smelting,cement production,and vehicle exhaust/gasoline contributed 23.2%±17.1%,19.0%±13.0%,and 10.3%±6.9%,respectively. The proportions of the anthropogenic sources gradually increased while geogenic source (riverine sediment) decreased from the coast to the outer shelf. This study demonstrated that the significant influence of atmospheric input of Pb contaminants into the ECS,and also the urgent need to control coal combustion and Pb discharge from industrial dust and fume emission in China. It also highlights the promising application of the Simmr model to quantify the proportions of multiple sources of trace elements in an environment.Keywords：lead contamination;Bayesian stable isotope mixing model;source quantification;surface sediment;core;Changjiang River estuary4|0|0Updated：2023-04-27
- Abstract：A new research proposal was introduced aiming at solving the fundamental theory for reducing the risk of hydrogen embrittlement (HE) in high-strength steels by utilizing hydrogen-consuming microorganisms. The superior performance of high-strength steel can meet the material strength requirements for remote deep-sea marine engineering development. Due to the heavy corrosive marine environment,steel structures must be protected by cathodic protection. However,high-strength steel is sensitive to stress corrosion cracking and HE,and cathodic protection can promote hydrogen permeation into steel. Hydrogen-consuming microorganisms are widespread in the natural environment and they utilize the energy of hydrogen oxidation to survive. If we could make use of the hydrogen-consuming function of microorganisms to consume the hydrogen generated during the cathodic protection process,then the potential for cathodic protection can be reasonably lowered,ideally protecting the steel and simultaneously reducing the possibility of HE.Keywords：hydrogen-consuming bacteria;high-strength steel;hydrogen permeation;hydrogen embrittlement (HE);mitigation4|0|0Updated：2023-04-27
Chemistry
- Abstract：Pico- and nano-eukaryotic plankton are important members of marine ecosystems. To understand their community structure and spatio-temporal variations in the Beibu Gulf, and to study the impact of Changjiang Nuclear Power Plant (CNPP) located in the northwest coast of the Hainan Island on the eukaryotic plankton, we studied these issues in the coastal water near CNPP bimonthly from February 2018 to January 2019 via 18S Illumina sequencing. The results reveal a higher genetic alphadiversity and less beta-diversity of the plankton community in small-size (0.45-5 μm and 5-20 μm) fractions than in large-size (20-200 μm and >20 μm) fractions. The small-sized phytoplankton, including Micromonas (Chlorophyta) and Minutocellus (Bacillariophyta), as well as heterotrophic plankton, including Paraphysomonas (Chrysophyceae), Ellobiopsis (Dinoflagellates), and Syndiniales (Dinoflagellates), took up a considerable proportion in eukaryotic plankton community. In addition, it showed a slight temperature increase and no significant difference in eukaryotic plankton community between the outfall of CNPP and other sampling sites, suggesting that the impact of the thermal discharge from the CNPP on local eukaryotic plankton community was limited.Keywords：nuclear power plant;the Beibu Gulf;eukaryotic plankton community;high-throughput sequencing;picoplankton;nanoplankton4|0|0Updated：2023-04-27
- Abstract：Twenty water bodies in China were sampled,and 186 strains of different Microcystis species were isolated,from which eight morphospecies were identified and 43 stains containing the mcyB gene were detected. Phylogenetic analysis based on the mcyB gene indicated that the microcystin (MC)-producing Microcystis in China could be divided into two groups (I and II) and showed significant differences between the two groups. The maximum sequence similarity was 69.1%. Microcystins (MCs) were measured by high-performance liquid chromatography (HPLC) analysis,and no microcystin-RR (MC-RR) was detected in some strains belonging to Group II. Compared to other regions of the world,the proportion of Chinese MC-producing Microcystis was different,and the regional differences were more obvious. A whole-cell polymerase chain reactio (PCR) assay was conducted to analyze the proportion of the mcyB gene in the laboratory cultured and field cultured Microcystis. The proportion of four morphospecies (M. vividis,M. ichthyoblabe,M. novacekii,and M. aeruginosa) that contained the mcyB gene exceeded 50% in the field cultured samples. Compared with former studies,M. aeruginosa was the most likely morphotype that can produce MCs in the world. This study provided new insight of Microcystis hazard assessment and field monitoring.Keywords：Microcystis;morphospecies;mcyB;16S rDNA;microcystin;high-performance liquid chromatography (HPLC)4|0|1Updated：2023-04-27
Ecology
- Abstract：Root rot disease caused by Fusarium solani is the most devastating disease of the tomato and legume crops in China. The metabolites of Bacillus species can inhibit many fungal diseases. In this study, the metabolites of deep-sea-derived bacterium Bacillus subtilis 2H11 can significantly inhibit the growth of F. solani. The metabolite C17-fengycin B, one of the cyclic lipopeptides, was identified by the combination of silica column chromatography, high-performance liquid chromatography (HPLC), high-energy collision induced dissociation mass spectrometry (HCD-MS) and tandem mass spectrometry (HCD-MS/MS). The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that C17-fengycin B could destroy the structure of the hyphae and spores of F. solani. The antifungal activities of C17-fengycin B against F. solani were tested at concentrations ranging from 0.05 mg/mL to 0.20 mg/mL. The results indicated that C17-fengycin B inhibited the growth of F. solani with antifungal index of 89.80% at 0.20 mg/mL, and the antifungal activity of C17-fengycin B was further verified by the pot experiment. In addition, the cytotoxicity experiment showed that C17-fengycin B had good biocompatibility and was a potential candidate for the development of biocontrol pesticide in the future.Keywords：Bacillus species;lipopeptide;fengycin;antifungal;pesticide4|0|4Updated：2023-04-27
- Abstract：The deep-sea is considered as the most extensive ecosystem on the Earth. It is meaningful for elucidating the life origins by exploring the origin and adaptive genetic mechanisms of the large deepsea organisms. Caridean shrimps have colonized and successfully adapted to deep-sea environments. They provide an ideal model to analyze the origin and adaptive evolution of modern deep-sea fauna. Here, we conducted the phylogenetic analyses of mitochondrial genomes (mitogenomes) from carideans, including 11 newly sequences reported in this investigation to explore the habitat origins, divergence times, and adaptive evolution of deep-sea (seamounts and hydrothermal vents) caridean shrimps. The results showed that the species of deep-sea Caridea formed a monophyletic group. Phylogenetic analysis supported that the deepsea caridean shrimps may originated from shallow sea. The hydrothermal vents alvinocaridid shrimps and Lebbeus shinkaiae from Thoridae underwent a second range expansion from seamounts to vent ecosystems. Estimates of divergence time showed that the caridean shrimps invaded into deep-sea at 147.75 Ma. The divergence of most of the modern seamount and hydrothermal vent species are in the late Cretaceous/early Tertiary. This may associate with the geological events of the Western Pacific, the climate change, and the global deep-water anoxic/dysoxic events during this period. Twenty-two potentially important adaptive residues were detected in the deep-sea shrimp lineage, which were located in atp6, atp8, cox1, cox3, cytb, nad2, nad4l, and nad5. This investigation adds our understanding of the evolutionary history of deep-sea caridean shrimps, and provides insights into the mitochondrial genetic basis of deep-sea adaptation in this group.Keywords：hydrothermal vents;seamounts;Caridea;mitochondrial genome;phylogenetic analysis;evolutionary history4|0|0Updated：2023-04-27
- Abstract：Although intestinal fungi play important roles in host health and disease, the composition and diversity of fungal communities remain poorly reported in fish. In this study, fungi in the fore-, mid-, and hindintestine of tilapia (Oreochromis mossambicus) and bighead carp (Aristichthys nobilis) from Hongchaojiang Reservoir in Guangxi, China were investigated by ITS sequencing. Based on this, we obtained 1 763 478 high-quality tags, which clustered into 1 089 operational taxonomic units (OTUs). In total, 404 OTUs were annotated, of which 310, 68, and 26 belonged to Ascomycota, Basidiomycota, and other, respectively. Results show significant differences in the community composition of intestinal fungi between tilapia and bighead carp but not within their different intestinal segments. Furthermore, 154 of the 404 annotated OTUs were considered reliable and were classified into three trophic modes and nine guilds. The three trophic modes consisted of 108 OTUs of saprotrophic fungi, 41 OTUs of pathotrophic fungi, and five OTUs of symbiotrophic fungi. The top three most abundant OTUs overall (i.e., Otu000002, Scopulariopsis acremonium; Otu000018, Alternaria palandui; Otu000034, Aureobasidium pullulans) showed lower abundance in the hind-intestinal segments of bighead carp, suggesting uneven distribution of these fungi in this species. In addition, saprotrophic and pathotrophic fungi were markedly decreased in the hindintestine. It is indicated that the fungal community was not only related to host species specificity but also to the respective physiological functions of different intestinal segments. These findings provide valuable information on the composition, structure, and potential function of the intestinal fungi community associated with different intestinal segments in tilapia and bighead carp under natural conditions, thus highlighting the importance of fungi as an integral part of the intestinal microbiota in maintaining host health.Keywords：fungi;intestinal microbiome;tilapia;bighead carp;Internal Transcribed Spacer (ITS) sequencing4|0|1Updated：2023-04-27
- Abstract：The large yellow croaker (Larimichthys crocea) is an important mariculture fish in China. Farmed large yellow croaker undergo periods of fasting to adapt to the environment or to improve meat quality. To better understand the physiological responses of their muscle tissues to fasting stresses, we analyzed the transcriptomes and proteomes of both normally-fed and fasting fish groups and identified 7 578 differentially expressed genes (DEGs) and 297 differentially expressed proteins (DEPs) among them. Gene ontology and KEGG analysis showed that the enriched biological pathways were mainly involved in various synthetic and catabolic pathways, especially the protein metabolism. Based on the omics data, nine DEGs related to muscle composition (CAN3, MYL3, and TNNC2), growth (MSTN and MYF5), autophagy (TSC2 and ULK1), and the ubiquitin proteasome pathway (PRS6B and UCHL3) were examined using qPCR. In response to fasting stress, MYL3 and TNNC2 were significantly downregulated, while genes associated with autophagy and the ubiquitin proteasome pathway were significantly upregulated. In response to fasting stress, MYL3, TNNC2, and MYF5 positively correlated with muscle growth were significantly downregulated, while inhibiting growth MSTN and genes associated with autophagy and the ubiquitin proteasome pathways were significantly upregulated. These results clarify the effects of fasting on metabolic changes in their muscle components and growth at the molecular level.Keywords：Larimichthys crocea;fasting;transcriptome;proteome;muscle4|0|1Updated：2023-04-27
- Abstract：Humpback grouper Cromileptes altivelis is one commercial fish with considerable economic value. To determine the expression stabilities of six commonly used internal reference genes in C. altivelis challenged by Vibrio harveyi and viral nervous necrosis virus (VNNV) through quantitative real-time PCR (qRT-PCR), the expression levels of selected genes in five immune organs stimulated with pathogenic infection were carefully evaluated using algorithms of geNorm, NormFinder, and BestKeeper. The results show that the expression stabilities of the six candidate internal reference genes were different. Under normal physiological conditions, RPL13 were identified as the most stably expressed genes among five different immune organs (liver, spleen, kidney, intestine, and gill). After V. harveyi stimulation, RPL13, RPL13, EF1A, RPL13, and EF1A were identified by geNorm, NormFinder, and BestKeeper as the most stable genes in liver, spleen, kidney, intestine, and gill, respectively. Combining these three algorithms suggested that under stimulation of VNNV, RPL13, EF1A, Actin, RPL13, and Actin were as the most stable genes in liver, spleen, kidney, intestine, and gill, respectively. These results suggest that specific experiment conditions and tissue types shall be considered when selecting the reference genes in qRT-PCR analysis. This study provided a solid foundation for future studies on gene expression of C. altivelis under different conditions.Keywords：Cromileptes altivelis;reference gene;expression stability;pathogenic infection4|0|5Updated：2023-04-27
Biology
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