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  Subjects -> WATER RESOURCES (Total: 160 journals)
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Journal of Oceanology and Limnology
Journal Prestige (SJR): 0.301
Citation Impact (citeScore): 1
Number of Followers: 4  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2096-5508 - ISSN (Online) 2523-3521
Published by Springer-Verlag Homepage  [2469 journals]
  • Metabolomic and proteomic responses of Phaeodactylum tricornutum to
           hypoxia

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      Abstract: Abstract Diatoms are important contributors to global net primary productivity, and play a crucial role in the biogeochemical cycles of carbon, phosphorus, nitrogen, iron, and silicon. Currently in some regions in the ocean, there’s a trend that carbon content is high while oxygen concentration is low, and the underlying mechanisms of diatoms’ response to low oxygen environments are worth investigating. Phaeodactylum tricornutum is a model diatom whose genome has been sequenced; it provides a universal molecular toolbox and a stable transgenic expression system. Therefore, the study of the responses of P. tricornutum to low oxygen has not only fundamental research significance but also important ecological significance. In this study, growth rates were determined and proteomic analysis and metabolomic analysis were performed to examine P. tricornutum responses under different oxygen concentrations (2% oxygen concentration for hypoxic condition and 21% oxygen concentration for the normal condition (sterilized air)). Results show that the hypoxic environment inhibited the growth of P. tricornutum. In the hypoxic conditions, P. tricornutum could reset its metabolism pathways, including enhancement in lipid utilization, replenishment of tricarboxylic acid (TCA) cycle through the glyoxylic acid cycle, and down-regulation of photorespiration to reduce energy waste. Additionally, the stress resistance mechanism was activated to facilitate the adaptation to low oxygen conditions. This study helps to reveal the different metabolic changes to hypoxia of diatom from that of higher plants, which might be ascribed to their different habitats and needs further exploration in the future.
      PubDate: 2022-07-07
       
  • Increased diversity and environmental threat of harmful algal blooms in
           the Southern Yellow Sea, China

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      Abstract: Abstract Harmful algal blooms (HABs) in the Southern Yellow Sea (SYS) have shown a trend of increasing diversity and detrimental effects. While the Bohai Sea, East China Sea, and South China Sea have experienced a high incidence of HABs since the 1980s, the Yellow Sea provides a relatively healthy ecological environment in which fewer HABs have been documented before the 21st century. Yet large-scale blooms of the green macroalga Ulva prolifera (so-called “green tides”) have occurred annually since 2007 in the Yellow Sea. Six people were poisoned and one person died in Lianyungang in 2008 due to ingestion of algal toxins. Moreover, the Yellow Sea experienced co-occurrence of harmful red tides, green tides, and golden tides in 2017. This combination of events, rare worldwide, indicates the potential for further deterioration of the marine environment in the Yellow Sea, which may be related to climate change, aquaculture, and other human activities. Using the SYS as an example, we collected data of the frequency and scale of HABs over the years, as well as that of marine algal toxins, and analyzed the trend in the diversity of HABs in the SYS, to explore the causes and impacts of HABs, as well as the interrelationships among different types of HABs, including harmful red tides, green tides, and golden tides. We also attempted to improve our understanding of HAB evolution under the influence of global climate change and intensified human activities.
      PubDate: 2022-07-07
       
  • Screening of nanobody against Microcystis from a human phage display
           nanobody library

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      Abstract: Abstract Microcystis species identification is essential for ecological studies and water bloom control. Immunoassays are more specific and convenient and several approaches have been used to develop for diagnosing harmful red tide algae. However, investigations on Microcystis identification using immunological approaches are still in the initial stage. In this study, Microcystis aeruginosa PCC7806 lysates were utilized as coated antigens to enrich and screen specific Microcystis nanobodies from a human domain antibody display library. After three rounds of enrichment, 10 positive monoclonal particles were isolated from the library and the most two positive nanobodies (DAb2 and Dab3) were effectively produced in Escherichia coli BL21. Finally, the DAb2 showed specific immune binding to different Microcystis by the immuno-dot blot assay. This antibody could be used to establish an immunological method to identify Microcystis.
      PubDate: 2022-07-07
       
  • Automatic calibration for wobble errors in shallow water multibeam
           bathymetries

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      Abstract: Abstract The wobble errors caused by the imperfect integration of motion sensors and transducers in multibeam echo-sounder systems (MBES) manifest as high-frequency wobbles in swaths and hinder the accurate expression of high-resolution seabed micro-topography under a dynamic marine environment. There are many types of wobble errors with certain coupling among them. However, those current calibration methods ignore the coupling and are mainly manual adjustments. Therefore, we proposed an automatic calibration method with the coupling. First, given the independence of the transmitter and the receiver, the traditional georeferenced model is modified to improve the accuracy of footprint reduction. Secondly, based on the improved georeferenced model, the calibration model associated with motion scale, time delay, yaw misalignment, lever arm errors, and soundings is constructed. Finally, the genetic algorithm (GA) is used to search dynamically for the optimal estimation of the corresponding error parameters to realize the automatic calibration of wobble errors. The simulated data show that the accuracy of the calibrated data can be controlled within 0.2% of the water depth. The measured data show that after calibration, the maximum standard deviation of the depth is reduced by about 5.9%, and the mean standard deviation of the depth is reduced by about 11.2%. The proposed method has significance in the precise calibration of dynamic errors in shallow water multibeam bathymetries.
      PubDate: 2022-07-07
       
  • Community structure of aerobic anoxygenic phototrophic bacteria in algae-
           and macrophyte-dominated areas in Taihu Lake, China

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      Abstract: Abstract Aerobic anoxygenic phototrophic bacteria (AAPB) represent a major group of bacterioplankton assemblages in many water systems and some are assumed to be closely associated with phytoplankton. However, studies on relationships between AAPB and cyanobacterial blooms are in scarcity. The dynamics of the abundance and diversity of AAPB was compared based on pufM gene in Meiliang Bay (featured by cyanobacterial blooms) and East Bay (featured by macrophyte) of Taihu Lake, a shallow subtropical lake in the East China plain. AAPB abundance was not significantly different between the two sites, and they were positively correlated with dissolved organic carbon (DOC) concentration. The ratios of AAPB to total bacteria varied from 3.4% to 11.5% and peaked in winter in both sites. No significant differences of AAPB community compositions were detected between the two sites, but there was a separation between warm seasons (June, August, and October) and cold seasons (December, February, and April). Rhizobiales and Limnohabitans-like pufM sequences were significantly contributors for the difference between two seasons, and specially enriched in cold seasons. Chlorophyll a (Chl a) and DOC were the most significant variables influencing the AAPB community structure. Furthermore, Porphyrobacter and Rhodospirillales-like pufM sequences were positively correlated with Chl a, indicating potential influence of cyanobacterial blooms on these AAPB taxa. These results suggested that diverse AAPB ecotypes coexisted in Taihu Lake, and their ecological role in carbon cycling in the lake may not be ignored.
      PubDate: 2022-07-07
       
  • The impact of the accumulation of algal blooms on reed wetlands in the
           littoral zones of Chaohu Lake

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      Abstract: Abstract In a large eutrophic lake, the littoral zone is normally an area with high-density elevated aquatic plant life, including algal blooms, where the presence of reed wetlands allows the accumulation of algae. In this study, the impact of accumulated algal blooms in reed wetlands in the littoral zones of Chaohu Lake was investigated seasonally from 2018 to 2019. The concentrations of chlorophyll a (Chl a), total nitrogen (TN), and total phosphorus (TP) were much higher in the reed-covered littoral zones (RCLZ) than in the unvegetated littoral zones (ULZ), indicating that more algal biomass was trapped and accumulated in the RCLZ. Algal biomass could be horizontally transported to downwind littoral zones under low wind speeds, favoring the establishment of blooms. Algal accumulation levels were highest in summer due to high water temperatures and algal biomasses. Likewise, the northern littoral zones were conducive to the development of large algal blooms because of the wind pattern. The values of TN, TP, Chl a, and loss on ignition in surface sediments were higher in the RCLZ than in the ULZ. Moreover, the diffusive fluxes of ammonium and soluble reactive phosphorus were also higher in the RCLZ than in the ULZ. Considering the capability of reed wetlands to trap algae, mechanical salvage and other physical methods should be adopted to eliminate algal biomass when massive blooms accumulate in the RCLZ.
      PubDate: 2022-07-07
       
  • Sodium acetate can promote the growth and astaxanthin accumulation in the
           unicellular green alga Haematococcus pluvialis as revealed by a proteomics
           approach

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      Abstract: Abstract Haematococcus pluvialis is an ideal natural source of strong antioxidant astaxanthin. Sodium acetate (NaAc) was proven an effective organic carbon source for improving algal growth and astaxanthin production; however, the underlying mechanism remains obscure. To reveal the mechanism of NaAc at the green vegetative stage of H. pluvialis, the physiochemical characteristics and the global protein expression profiles obtained using a tandem mass tag labeling approach were compared between the control (CK) and two NaAc-addition groups. Results show that after NaAc addition, the biomass, nitrate consumption rate, and activities of three carbohydrate metabolism enzymes of H. pluvialis were significantly increased, and the net photosynthetic rate and chlorophyll content decreased. In addition, astaxanthin, total carbohydrates, and total lipids were accumulated, and some red cells appeared in the NaAc5 group. Moreover, 317 differentially expressed proteins (DEPs) with the most altered expression patterns were screened out in the CK vs. NaAc5 comparison in our proteomics study. All the DEPs involved in carbohydrate metabolism and lipid metabolism were significantly increased, while most of the photosynthesis-related proteins were depressed in the two NaAc-treated groups. The proteomics results were verified and supported by parallel reaction monitoring approach and physiochemical data. Our findings demonstrate that NaAc promoted the tricarboxylic acid cycle, glyoxylate cycle, and amino acid and lipid synthesis, and inhibited the photosynthesis-related activities, which consequently speeded up the growth and astaxanthin accumulation in this alga.
      PubDate: 2022-07-07
       
  • Competitiveness of alga Microcystis aeruginosa co-cultivated with
           cyanobacterium Raphidiopsis raciborskii confirms its dominating position

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      Abstract: Abstract Microcystis aeruginosa has always been regarded as the main culprit of cyanobacterial blooms in freshwater. However, in recent years, Raphidiopsis raciborskii has gradually replaced M. aeruginosa as the culprit of cyanobacterial blooms in some tropical and subtropical shallow lakes. To reveal which one plays a more dominant role, interactions between cylindrospermospin (CYN)-producing R. raciborskii and microcystins (MCs)-producing or non-MCs-producing M. aeruginosa strains were studied using bialgal cultures at different initial ratios of biomasses of the two species at 25 °C. During the co-cultivation, the M. aeruginosa strains inhibited the growth and heterocyst formation of R. raciborskii filaments, and thus occupied a dominant position during the co-cultivation regardless of the initial biomass ratios in the cultures. In addition, the MCs-producing M. aeruginosa strain contributed to a higher portion of the total biomass and exerted a stronger inhibitory effect on R. raciborskii compared with the non-MCs-producing strain. However, the growth of both MCs-producing and non-MCs-producing M. aeruginosa strains was stimulated by R. raciborskii in the co-cultures compared with M. aeruginosa monoculture, indicating that M. aeruginosa could outcompete R. raciborskii if given enough time, enabling it to develop into the dominant species even in very low initial concentration. To our best knowledge, this is the first report on the loss of heterocyst formation by a species of cyanobacteria that resulted from interactions between two different species of cyanobacteria. These findings indicate that it is difficult for R. raciborskii to replace the dominant position of M. aeruginosa under the experimental environmental condition, and the allelopathic effects of M. aeruginosa on R. raciborskii could significantly contribute to the success of M. aeruginosa.
      PubDate: 2022-07-07
       
  • Physiological and molecular responses of invasive cyanobacterium
           Raphidiopsis raciborskii to ambient phosphorus deficiency

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      Abstract: Abstract Raphidiopsis raciborskii can cause harmful cyanobacterial blooms when concentrations of environmental phosphorus (P) are very low, thus the physiological and molecular mechanisms involved in the acclimation to P need to be characterized better. The growth, chlorophyll fluorescence, alkaline phosphatase, and expression of genes directly involved in P assimilation were compared in the R. raciborskii FACHB 1496 strain grown with and without inorganic P. The specific growth rate (μ), Chl a, and six fluorescence parameters (minimal fluorescence (F0), maximal fluorescence (Fm), maximal variable fluorescence (Fv), electron transport flux (further than QA) per RC (ET0/RC), quantum yield of the electron transport in PSII (ØE0), and the probability that an electron from a trapped exciton is moved into the electron transport chain beyond Q A − (ψ0)) markedly decreased in R. raciborskii in response to experimental P-deficiency. In contrast, the relative variable fluorescence at the J-step (VJ), trapped energy flux (leading to QA reduction) per RC (TR0/RC), and alkaline phosphatase activity significantly increased. In addition, gene expressions involved in the alkaline phosphatase (phoA1 and phoA2), high-affinity inorganic P transporter (pstS1), phosphonate transporter and metabolism (phnD and phnM), and nucleotidase (nucH) were significantly upregulated under P deficiency. However, physiological and molecular responses were resumed rapidly after P re-supplementation following P-deficient conditions. Our results highlight that R. raciborskii can perform coordinated and complex cellular and physiological responses to cope with P deficiency, reflecting R. raciborskii’s multi-faceted machinery to respond to environmental P fluctuations.
      PubDate: 2022-07-07
       
  • Overview of the distribution and adaptation of a bloom-forming
           cyanobacterium Raphidiopsis raciborskii: integrating genomics, toxicity,
           and ecophysiology

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      Abstract: Abstract Raphidiopsis raciborskii is a notorious bloom-forming and filamentous cyanobacterium that has been extensively investigated into its toxicity, phylogeny, and spreading potential. Studies have demonstrated that this species has spanned different climates from tropical zones to temperate regions, suggesting that R. raciborskii is becoming a cosmopolitan species in freshwater systems around the world. In fact, it has been proposed that several characteristics of R. raciborskii may explain its spread and dominance. In particular, R. raciborskii is known to display a high extent of physiological plasticity regarding nutrients, light regimes, and temperatures. Moreover, this species illustrates different ecotypes with distinct environmental requirements. Here, we present an overview of R. raciborskii’s global distribution and adaptation strategy based on the recent findings from genome variance, toxicity, and ecophysiology. The expansion of its geographical distribution can be linked to its genome, toxicity, and ecophysiology. The variable genes are mainly associated with the stress response, phage defense, DNA repair, cell cycle control, and membrane transport, illustrating the species’ adaptability in response to changing environments. In fact, the species shows rapid adaptability to low and/or variable nutrient availability, especially changing phosphorus availability. Moreover, the variabilities of strains within the population extend their flexibility to adapt and acclimate to ambient environment. In addition, cylindrospermopsins (CYN) appear to have a potential biological role in facilitating theirs dominance or bloom. These strategies of R. raciborskii make it a challenge to manage in a freshwater system, reflecting the management of its bloom from further evidence of the complex ecophysiology, toxicity, and genome of this species.
      PubDate: 2022-07-07
       
  • 16S rRNA gene sequencing analysis on changes in the intestinal flora of
           Procambarus clarkii with “Black May” disease

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      Abstract: Abstract The morbidity and mortality peak of farmed Procambarus clarkii occurs around May every year, a phenomenon known as “Black May” disease (BMD). Increasing evidence shows that the intestinal flora is closely related to host health. We analyzed and compared the microbiota of healthy and BMD-affected P. clarkii intestines. The results show that there was no significant difference in bacterial α-diversity (richness P=0.59; evenness P=0.43; and diversity P=0.052) between the diseased group and the control group. Four dominant phyla in the intestines of crayfish in the control group, namely Tenericutes (30.86%), Bacteroidetes (29.99%), Firmicutes (22.23%), and Proteobacteria (15.23%), were identified. However, a striking shift in the microbial composition were found in the intestines of P. clarkii with BMD. Bacteroidetes was a dominant phylum in healthy P. clarkii, whereas the prevalence was low in diseased P. clarkii (1.87%). By contrast, the prevalence of Proteobacteria was significantly higher (P<0.05) in P. clarkii with BMD than in P. clarkii without BMD. Candidatus Bacilloplasma, Bacteroides, Vibrio, and Aeromonas showed significant differences (P<0.05) at the genus level. Tax4Fun function prediction indicated that the relative abundance of genes involved in energy metabolism in the intestinal flora of P. clarkii with BMD was significantly reduced (P<0.05). Therefore, BMD can change the composition of the intestinal microbiota of P. clarkii. This study contributes to the understanding of the relationship between intestinal flora and host especially in aquatic animals.
      PubDate: 2022-07-07
       
  • The near-inertial waves observed east of the Philippines

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      Abstract: Abstract Based on mooring observations from Aug. 1, 2016 to Dec. 14, 2017, the characteristics and underlying mechanisms of near-inertial waves (NIWs) observed east of the Philippines were studied. Three strong NIW events were investigated in detail. The NIWs in Event I were induced by typhoon Lan and had the strongest magnitudes of 0.35 m/s. The maximum near-inertial kinetic energy (NIKE) was shown at the ocean surface. The NIW in Event II was stimulated by a moderate cyclonic wind with the extreme NIKE located at about 110-m depth. The existence of a cyclonic eddy during Events I and II led to a blue shift of near-inertial frequencies. For Event III, the surface near-inertial signals were also induced by local weak wind, whereas the real generation mechanisms for the subsurface NIWs remain unclear. In particular, during Event III, there was a nonlinear wave-wave interaction between NIWs and semidiurnal (D2) tides, which further induced strong D2±f waves. Overall, the NIWs in the three events exhibited distinct vertical structures. The NIWs in Events I and II were dominated by lower modes with elevated NIKE well confined to the upper 250 m and 270 m, respectively. In contrast, the NIW Event III was dominated by higher modes and the NIWs penetrated downward beyond 360 m. Such deep penetration of NIWs could be attributed to the weak wind stress curl and positive sea level anomalies associated with an anticyclonic eddy. In addition, the three NIW events had e-folding timescales of less than 7 days.
      PubDate: 2022-07-07
       
  • Reconstruction of large complex sand-wave bathymetry with adaptive
           partitioning combining satellite imagery and sparse multi-beam data

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      Abstract: Abstract Shallow marine sand waves are formed on the seabed and are widely distributed within tidal environments. However, the use of multibeam echo sounding (MBES) is costly to obtain the bathymetric mapping of large complex sand waves. Therefore, we propose a new method that employs a combination of multiangle sun glint images and sparse MBES data to achieve comprehensive bathymetric mapping of large and complex sand waves. This method involves estimating sea surface roughness, automatically extracting sand-wave crests, conducting adaptive subregion partitioning, estimating the water depth at auxiliary points, and generating digital bathymetric models. The method was employed in a case study of sand waves on the Taiwan Bank. Bathymetric mapping was implemented for large complex sand waves over an area spanning approximately 350 km2 using multiangle sun glint images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer and MBES data. The results show that mapped and measured water depths were well-matched; the root-mean-square error of water depths was 1.77 m, and the relative error was 5.03%. These findings show that bathymetric mapping of large complex sand waves can be effectively conducted using the new method, and as such, the workload of MBES is reduced and efficiency is improved.
      PubDate: 2022-05-31
       
  • UV-B irradiation and allelopathy by Sargassum thunbergii affects the
           activities of antioxidant enzymes and their isoenzymes in Corallina
           pilulifera

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      Abstract: Abstract Intertidal macroalgae can cope with the dual effects of UV-B irradiation and allelopathy. To study the impacts of the two stressors, we co-cultured Corallina pilulifera with Sargassum thunbergii in 1:1 and 1:10 ratios under different doses of UV-B radiation. The response of the antioxidant defense system, focusing on activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POX) and glutathione reductase (GR), was monitored. In addition, isoenzyme patterns were analyzed using non-denaturing polyacrylamide gel electrophoresis. The results show that the activities of SOD, APX, and GR were all significantly affected by both UV-B radiation and allelopathy, and the effect of their interaction was significant. However, POX activity was only influenced by UV-B radiation. The enzymatic assay revealed four distinct bands of SOD. The SODIII band weakened significantly when the co-cultures were exposed to extremely high dosage of UV-B irradiation under both co-culturing ratios of 1:1 and 1:10. When the co-culturing ratio was 1:10, both POXII and APXII enzyme activities increased with different UV-B doses. GR activity was at its greatest when the co-culture ratio was 1:10 and exposure was to the higher UV-B doses. The activities of GRIII and GRIV were elevated under all UV treatments whereas the activities of GRI and GRII were reduced under the lower UV-B treatments but were elevated under the higher UV-B treatments. However, lipid peroxidation, as indicated by the thiobarbituric acid-reacting substance (TBARS) assay, increased significantly under the dual stressors. Our data suggest that allelopathy and UV-B radiation stress can each affect the antioxidant enzyme activities of C. pilulifera. Critically, the adverse effects of UV-B on C. pilulifera were intensified by the compounding effects of allelopathy.
      PubDate: 2022-05-31
       
  • Stoichiometric flexibility regulates the co-metabolism effect during
           organic carbon mineralization in eutrophic lacustrine sediments

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      Abstract: Abstract Several studies have suggested the pivotal roles of eutrophic lakes in carbon (C) cycling at regional and global scales. However, how the co-metabolism effect on lake sediment organic carbon (OC) mineralization changes in response to integrated inputs of labile OC and nutrients is poorly understood. This knowledge gap hinders our ability to predict the carbon sequestration potential in eutrophic lakes. Therefore, a 45-day microcosm experiment was conducted to examine the dominant mechanisms that underpin the co-metabolism response to the inputs of labile C and nutrients in lacustrine sediments. Results indicate that the labile C addition caused a rapid increase in the positive co-metabolism effect during the initial stage of incubation, and the co-metabolism effect was positively correlated with the C input level. The positive co-metabolism effect was consistently higher under high C input, which was 152% higher than that under low C input. The higher β-glucosidase activity after nutrient addition, which, in turn, promoted the OC mineralization in sediments. In addition, different impacts of nutrients on the co-metabolism effect under different C inputs were observed. Compared with the low nutrient treatments, the largest co-metabolism effect under high C with high nutrient treatment was observed by the end of the incubation. In the high C treatment, the intensity of the co-metabolism effect (CE) under high nitrogen treatment was 1.88 times higher than that under low nitrogen condition. However, in the low C treatment, the amount of nitrogen had limited impact on co-metabolism effect. Our study thus proved that the microorganisms obviously regulate sediment OC turnover via stoichiometric flexibility to maintain a balance between resources and microbial requirements, which is meaningful for evaluating the OC budget and lake eutrophication management in lacustrine sediments.
      PubDate: 2022-05-31
       
  • Influence of nitrate concentrations on EH40 steel corrosion affected by
           coexistence of Desulfovibrio desulfuricans and Pseudomonas aeruginosa
           bacteria

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      Abstract: Abstract Nitrate addition is a common bio-competitive exclusion (BCE) method to mitigate corrosion in produced water reinjection systems, which can affect microbial community compositions, especially nitrate and sulfate reducing bacteria, but its effectiveness is in controversy. We investigated the influence of nitrate concentrations on EH40 steel corrosion affected by coexistence of Desulfovibrio vulgaris and Pseudomonas aeruginosa bacteria. Results demonstrate that only mixed bacteria or nitrate had little effect on EH40 steel corrosion, and nitrate could accelerate the corrosion of EH40 steel through the action of microorganisms. The corrosion promotion of nitrate was dependent on its concentrations, which increased from 0 to 5 g/L and decreased from 5 to 50 g/L. These differences were believed to be related to the regulation of nitrate in the growth of bacteria and biofilms. Therefore, care must be taken to BCE method with nitrate when nitrate reducing bacteria with high corrosive activity are present in the environments.
      PubDate: 2022-05-31
       
  • Diverse habitat preferences of two sea cucumber species and the seasonal
           change in a coral reef area

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      Abstract: Abstract Different sea cucumbers have different preferred habitats and seasonal changes, which is still lack of detailed research. This study selects two common tropical sea cucumbers (Holothuria edulis and Stichopus chloronotus) to explore the reasons that affect their habitat selection and seasonal changes, so as to provide support for the spatial planning of sea cucumbers reserve in coral reef area. The study area is a compound distribution area of living coral reefs and sandy bottom in the north of Wuzhizhou Island. The survey time is January, April–September, 2019. Three fixed transects (G, H, and Q) were selected to reveal the population ecological characteristics of them in the typical dry season (January, April, May, and June) and rainy season (July, August, and September). The variation range of density for H. edulis and S. chloronotus were 2.0–8.9 inds./10 m2 and 0.2–0.7 inds./10 m2, respectively. The population density in rainy season was significantly higher than that in dry season (P<0.05). H. edulis tends to be distributed in deeper water. The distribution of H. edulis was significant positively correlated with the sand coverage and sand continuity in G transect (P<0.05), and significant negatively correlated with live coral coverage in three transects (P<0.01). The shift from dry season to rainy season is a key factor affecting their habitat preference. In dry season, the preferred habitats of S. chloronotus are small rock (SR), sand (S), and small coral reef (SCR), while the H. edulis is S, SR, and dead coral rubbles (DCR). In rainy season, the preferred habitats of S. chloronotus are shift to SCR and SR, while the H. edulis is SCR, DCR, and sand.
      PubDate: 2022-05-31
       
  • Seasonal co-occurrence patterns of bacteria and eukaryotic phytoplankton
           and the ecological response in urban aquatic ecosystem

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      Abstract: Abstract Microorganisms play a key role in aquatic ecosystems. Recent studies show that keystone taxa in microbial community could change the community structure and function. However, most previous studies focus on abundant taxa but neglected low abundant ones. To clarify the seasonal variation of bacterial and microalgal communities and understand their synergistic adaptation to different environmental factors, we studied the bacterial and eukaryotic phytoplankton communities in Fenhe River that runs through Taiyuan City, central China, and their seasonal co-occurrence patterns using 16S and 18S rDNA sequencing. Results indicate that positive interaction of eukaryotic phytoplankton network was more active than negative one except winter, indicating that the cooperation (symbiotic phenomenon in which phytoplankton are interdependent and mutually beneficial) among them could improve the adaption of microbial community to the local environmental changes and maintain the stability of microbial network. The main genera that identified as keystone taxa in bacterial network were Salinivibrio and Sphingopyxis of Proteobacteria and they could respond to the variation of nitrite and make use of it, while those that identified as keystone taxa in eukaryotic phytoplankton network were Pseudoschroederia and Nannochloris, and they were more susceptible to nitrate and phosphate. Mychonastes and Cryptomonas were closely related to water temperature. However, the loss of the co-occurrence by environmental factor changes affected the stability of network structure. This study provided a reference for analyzing relationship between bacteria and eukaryotic phytoplankton and revealing potential importance of keystone taxa in similar ecological domains in carbon, nitrogen, and phosphorus dynamics.
      PubDate: 2022-05-31
       
  • Estimating the evolution of sea state non-Gaussianity based on a
           phase-resolving model

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      Abstract: Abstract The occurrence of rogue waves is closely related to the non-Gaussianity of sea states, and this non-Gaussianity can be estimated using corresponding two-dimensional wave spectra. This paper presents an approach to non-Gaussianity estimation based on a phase-resolving model called the high-order spectral method (HOSM). Based on numerous HOSM simulations, a set of precalculated non-Gaussianity indicators was established that could be applied to real sea states without any calibration of spectral shapes. With a newly developed extraction approach, the indicators for given two-dimensional wave spectra could then be conveniently extracted from the precalculated dataset. The feasibility of the newly developed approach in a real wave environment is verified. Using the estimation approach, phase-resolved non-Gaussianity can now be illustrated throughout the evolution of sea states of interest, not just at a few specific times; and the level of non-Gaussianity at any time in a duration can be identified according to the statistics (e.g., quantities) of the phase-resolved indicators, that are obtained throughout the duration concerned.
      PubDate: 2022-05-31
       
  • Changes in embryonic development, juvenile growth and physiological
           adaptation of the cuttlefish Sepia pharaonis in response to photoperiod
           manipulation

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      Abstract: Abstract Photoperiod is a key environmental indicator for regulating embryonic development, individual growth and physiological processes in aquatic animals. In this study, differences in embryonic development and performance of newly hatched cuttlefish juvenile exposed to five different cycles of lightdark (L:D): constant light, 18L:6D, 12L:12D, 6L:18D cycles, and constant darkness were evaluated. Prolonged exposure to light induced an accelerated rate of embryonic development, particularly after the red-bead stage. Principal component analysis (PCA) revealed that red-bead stage, heartbeat, endoskeleton formation, pigment appear, and six increments of cuttlebone were the main factors contributing to the embryonic development. Meaning that the duration time of these five stages were significantly different when exposed to photoperiod regimes, which may determine the duration of the incubation period of the embryos. Long term light has also affected the incubation parameters with an increased rate in hatching and shortened the incubation and hatching periods in the 12–24-h day length range. However, constant light and darkness environment appeared to have a greater effect on the stress of embryonic development, mainly reflected in the yolk shed ratio and the inking rate in the egg capsule. Moreover, the increase in the day length has contributed to improve the growth and survival of juveniles in the 12–18-h day length range; however, juveniles exposed to constant light and darkness experienced worse results in terms of growth, tissue glycogen content, digestive enzymes of the digestive glands, and metabolic enzymes of the muscles. These finding suggest that prolonged light exposure accelerates the process of embryonic development, maximum feeding time is not necessarily a condition of optimal growth, and inappropriate light cycles can disturb the body’s endogenous controls. Therefore, the optimal photoperiod for the embryos development and juvenile growth of Sepia pharaonis were 12 h and 12–18 h of day length, respectively. These results are useful for increasing the production of this species during embryo incubation and juveniles rearing in aquaculture practice.
      PubDate: 2022-05-31
       
 
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