Coastal Seawater Research Articles

Time-decay patterns and irregular disturbance: contrasting roles of abundant and rare microbial communities in dynamic coastal seawater.

The relative importance of rare and abundant taxa in microbial temporal patterns remains debated. Here, we identified taxonomically associated distinct diversity modes of abundant and rare subcommunities from a year-round time-series study in dynamic coastal seawater. We highlighted the significance of the rare subcommunity in maintaining community stability by serving as a repository to offer specialists driven by stochastic processes over time. The abundant subcommunity, by contrast, contributed mainly to temporal rhythmic variations. This study expands the current understanding of the temporal dynamics and stability of coastal microbial communities by revealing distinct variation patterns of subcommunities with different abundances.

A Comprehensive Genome Mining Analysis of Biosynthetic Gene Clusters in Pseudomonas sp. SXM-1

Very resistant pathogenic microorganisms have been reported to current antibiotics in the last decade. Therefore, there is a great need to understand not only resistance metabolism but also secondary metabolites of pathogenic microorganisms. Genome mining tools have so far been improved to understand secondary metabolites from biosynthetic gene clusters. Microorganisms predicted for their genomes and secondary metabolites using these tools are widely employed in pharmaceutical and industrial studies. Pseudomonas spp. are widely used in recombinant DNA technology to produce commercial products. Bioinformatics-based in silico tools significantly contribute to the discovery of new bioactive compounds for pharmacy and medicine. This study aims to conduct a comprehensive gene cluster analysis of the Pseudomonas sp. SXM-1 strain isolated from the coastal seawater of Xiamen Bay using antiSMASH (7.0.1). The accession number of Pseudomonas sp. SXM-1 strain was retrieved from NCBI. 14 regions were found, including non-ribosomal peptides metallophores (NRP-metallophore), nonribosomal peptide-synthetase (NRPS), NRPS-like, ribosomally synthesized and post-translationally modified peptide-like (RiPP-like), betalactone, nonribosomal peptide-synthetase (NRPS), ectoine and N-acetylglutaminylglutamine amide (NAGGN). Analysis of all 14 regions revealed secondary metabolites with potential applications in diverse fields. Microbiologists are strongly advised to conduct wet-lab experiments to validate the secondary metabolites discussed in this study.

The value of information in predicting harmful algal blooms

Environmental decision-making is inherently subject to uncertainty. However, decisions are often urgent, and whether to take direct action or invest in collecting additional data beforehand is pervasive. To make this trade-off explicit, the value of information (VoI) theory offers a powerful decision analytic tool to quantify the expected benefit of resolving uncertainty in a decision context. Although it is mainly used in economic contexts, it can be applied to biodiversity conservation and management.In our approach, we evaluate the expected surplus in resolving uncertainty about the occurrence of harmful algal blooms (HABs) in the German North Sea coastal waters and the effect on decision-making. We use an established dynamic foodweb model (NPPZ) with two competing phytoplankton consortia (harmful, non-harmful) and regional monitoring data to analyse the prediction accuracy of different indicators. Our analysis revealed a prediction accuracy of a HAB occurrence of 0.65 % if additional information on zooplankton is included. We then evaluate the effect of reducing uncertainty about these indicators (e.g., through extended monitoring) on management decisions employing a VoI analysis. We find that additional information may lead to an expected welfare gain of up to 2.67 million Euro in our decision context. Our results highlight the significant potential for VoI analysis to enhance decision-making in fishery and ecosystem management and provide insights for future monitoring strategies to mitigate the adverse effects of HABs. This approach contributes valuable methodological insights for optimising management strategies and further emphasises the importance of considering uncertainty in decision-making processes.

Integrated Cultivation of Land-Sea Ecosystems That Prioritizes Harmony with Nature and Society

Integrated Cultivation of Land-Sea Ecosystems That Prioritizes Harmony with Nature and Society

Metagenomic Analysis of Microbial Diversity in the Moroccan Coastal Water of the Gibraltar Strait

Coastal waters are known for higher productivity and organic matter levels, which support a high diversity and abundance of microorganisms compared to some aquatic environments. The characterization of marine microbiomes can provide valuable information for evaluating the sustainability of coastal waters that are increasingly subjected to environmental and human impacts. Our study is the first metagenomic study realized on Moroccan Mediterranean coastal seawater. We analyzed and described the Gibraltar Detroit marine microbiome taxonomic and functional profiling using MG-RAST software. Shotgun sequencing revealed a predominance of bacterial taxa, particularly the Proteobacteria (57.29%) and Bacteroidetes (27.06%) phyla, alongside notable populations of eukaryotes, viruses, and archaea. Alphaproteobacteria and Gammaproteobacteria emerged as the dominant bacterial classes, while Flavobacteria represented a significant portion of Bacteroidetes. Functional profiling of the microbial community highlighted a wide array of metabolic pathways, emphasizing genes related to carbohydrate metabolism, amino acid synthesis, and protein processing. The marine microbiome exhibited essential biogeochemical activities, particularly in nitrogen, sulfur, and carbon cycles, with notable pathways including denitrification, thiosulfate oxidation, and carbon fixation. This functional diversity underlines the microbiome’s role in sustaining ecosystem health through nutrient cycling and organic matter degradation. Our findings offer a crucial baseline for understanding microbial community structure and resilience in Mediterranean coastal ecosystems, with implications for assessing future environmental and anthropogenic impacts on these microbial dynamics.

Microplastic pollution in coastal surface seawater of Southern Vietnam.

Microplastics have recently emerged as a significant environmental concern due to their direct impacts on marine ecosystems. Vietnam, with its 3260-km coastline, faces an elevated risk of microplastic pollution due to various coastal anthropogenic activities. This study explored microplastic distribution in coastal surface seawater in the Southern Vietnam regions of Tien Giang, Can Gio, and Vung Tau. A total of 45 samples were collected in April, 2019, and the results showed that microplastics present at all sampling sites, with the abundance varying from 0.074 ± 0.109 pieces/m3 in Can Gio to 0.56 ± 0.35 pieces/m3 in Tien Giang. Estuarial sites showed higher abundances for all regions. Most microplastics were under 2.8mm, fragmented, and primarily white or transparent. Polypropylene, polyethylene, and ethylene-vinyl acetate were the dominant polymers. This research indicates the urgency of further investigations to comprehensively understand the influence of wind patterns and other environmental factors on microplastic distribution.

Краткосрочный прогноз смерчеопасных ситуаций для прибрежной акватории Черного моря с использованием усовершенствованного индекса WRI

The paper considers the issues of improving the quality of short-term forecasts of waterspout-risk conditions for the Black Sea coastal water. The results related to the development of new versions for calculating the regional waterspout risk index (WRI) for both the warm (WRI21) and cold (WRIW) seasons are presented. The WRI is used to identify zones of high-risk waterspout formation and subsequent localization of waterspout-risk areas of the coast. Calculations of the WRI fields are based on the output of the COSMO-Ru2 mesoscale model with a grid spacing of 2.2 km. Calculations are carried out in real time within the technology for assessing the risk of waterspouts. The skill of forecasting new WRI versions for different periods is analyzed. It is shown that the probability of waterspout detection in the warm season can reach 82% on average. At the same time, there is also a high false alarm rate (about 70%), mainly due to the excessively predicted waterspout risk in certain areas of the coast (Sochi and Tuapse). In the cold season, as expected, a significantly smaller number of waterspout-risk days is predicted as compared to the warm period. Examples of forecasts for different seasons are presented. Recommendations on the use of forecasts for preparing storm warnings are given.

Screening and functional characterization of isocitrate lyase AceA in the biofilm formation of Vibrio alginolyticus.

Biofilm is a well-known sessile lifestyle for bacterial pathogens, but a little is known about the mechanism on biofilm formation in Vibrio alginolyticus. In this study, we screened V. alginolyticus strains with strong biofilm formation ability from coastal seawater. The antibiotic resistance of the biofilm cells (BFs) was higher than that of the planktonic cells (PTs). To study the genes and pathways involved in biofilm formation, we performed transcriptome analysis of the BFs and PTs of V. alginolyticus R9. A total of 685 differentially expressed genes (DEGs) were upregulated, and 517 DEGs were downregulated in the BFs. The upregulated DEGs were significantly enriched in several pathways including glyoxylate and dicarboxylate metabolism, while the downregulated genes were significantly enriched in the flagellar assembly pathways. The key gene involved in glyoxylate shunt, aceA, was cloned, and ΔaceA mutant was constructed to determine the function of AceA in carbon source utilization, biofilm formation, and virulence. Real-time reverse transcription PCR showed that the expression of aceA was higher at the mature stage but lower at the disperse stage of biofilm formation, and the expression of the flagellar related genes was upregulated in ΔaceA. This is the first study to illustrate the global gene expression profile during the biofilm formation of V. alginolyticus, and isocitrate lyase AceA, the key enzyme involved in glyoxylate shunt, was shown to maintain biofilms accompanied by downregulation of flagellation but promoted dispersal of BFs at the late stage.IMPORTANCEBiofilms pose serious public problems, not only protecting the cells in it from environmental hazard but also affecting the composition and abundance of bacteria, algae, fungi, and protozoa. The important opportunistic pathogen Vibrio alginolyticus is extremely ubiquitously present in seawater, and it also exhibited a strong ability to form biofilm; thus, investigation on the biofilm formation of V. alginolyticus at molecular level is fundamental for the deeper exploration of the environmental concerns arose by biofilm. In this study, transcriptome analysis of biofilm cells (BFs) and planktonic cells (PTs) from V. alginolyticus was performed and AceA was screened to play an important role in biofilm formation. AceA was shown to maintain biofilms accompanied by downregulation of flagellation but promoted dispersal of BFs at the disperse stage. This method was helpful to further understand the ability and mechanism of V. alginolyticus biofilm formation and provide clues for prevention of V. alginolyticus infection.

Multielement electrochemical vapor generation system coupled with atomic fluorescence spectrometer for simultaneous measurement of trace levels of As and Hg in coastal seawater samples

BackgroundToxic elements As and Hg in coastal waters affect human health through the food chain even at trace levels. The simultaneous determination of As and Hg in seawater using electrochemical vapor generation (ECVG) with atomic fluorescence spectrometer (AFS) currently has technical bottlenecks. One is the need for a simple and efficient chemical reaction cell and corresponding parameters to generate both AsH3 and Hg vapors, and the other is a suitable preservation method of the mixed standard solutions. ResultsA novel, efficient, online ECVG device was developed and interfaced with a laboratory-built multichannel AFS. The electrolytic cell adopted Sn–Pb alloy as the cathode material to generate both AsH3 and Hg vapors by electrolysis, replacing the unstable reagent tetrahydroborate (THB) usually used in most traditional vapor generation methods. The AFS was equipped with a built-in H2 generator for fuel supply, instead of the conventional acid-THB system. A mixed standard solution of As and Hg was prepared and preserved using thiourea-ascorbic acid as a fixing agent for Hg and a prereduction agent for As(V). The method detection limits (LOD, 3σ) were 0.005 and 0.003 μg/L for As and Hg, respectively. The relative standard deviations (RSD, n = 8) of the spiked samples were 2.8 % (0.50 μg/L As) and 3.1 % (0.05 μg/L Hg), respectively. The recoveries of standard spiked seawater samples with different salinities ranged from 86.1 % to 115.3 %. SignificanceThe system has been successfully applied to the simultaneous analysis of As and Hg in the seawater samples collected from the Xiamen coastal area. The study results provide a sensitive, accurate, and efficient method to promote the development and utilization of simultaneous analysis of multielement in seawaters.

Unveiling the effects of dissolved organic matter (DOM) extracted from coastal algae and river on the photooxidation of arsenite

The coastal environment is an important ecosystem connecting land and sea, and arsenite (As(III)) in coastal seawater can seriously affect human health through the food chain. However, the effects of dissolved organic matter (DOM) extracted from coastal algae and rivers on As(III) photooxidation remain unclear. Results show that coastal algal DOM (CA-DOM) is significantly more effective than Suwannee River natural organic matter (SRNOM) in photooxidation of As(III), with a rate 8.3 times higher after correcting for light screening effects. CA-DOM accelerates As(III) photooxidation mainly through the 3DOM⁎ pathway, contributing 78.7 % to the process, whereas 3NOM⁎ contributes only 37.2 % for SRNOM. CA-DOM consists primarily of low-excited tyrosine and tryptophan-like protein substances, whereas SRNOM consists of humic and fulvic acid-like substances. Thus, CA-DOM exhibits a higher steady-state concentration of 3DOM⁎, and the 3DOM⁎ reacts much faster with As(III) than the 3NOM⁎. The increase in CA-DOM concentration can significantly accelerate the photooxidation of As(III), whereas the effect of SRNOM concentration is negligible. Increased salinity can accelerate As(III) photooxidation for all types of DOM. Our results provide new insights into the role of DOM from different sources in the photooxidation of As(III) in the natural environment or engineering applications.

Release of intracellular enzymes increases the total extracellular activities of carbohydrate processing enzymes in marine environment.

Microbial extracellular enzymatic activities (EEAs) produced by microbes to degrade biopolymers are the 'gatekeeper' of carbon cycle in the marine ecosystem. It is usually assumed that these extracellular enzymes are actively secreted by microbes. But biopolymers degrading enzymes also exist in the intracellular space. Cell lysis will passively release these enzymes into the environments and contribute to the total EEAs. However, to what extent the cell lysis can contribute to the total EEAs are still unclear. Here, using extreme cell lysis method, we evaluated the maximum contribution of cell lysis to total EEAs in culturable marine bacteria and coastal seawater. For carbohydrate processing enzymes (β-glucosidase, alginate lyase and chitinase), the release of intracellular enzymes could contribute positively (up to 56.1% increase for β-glucosidase in seawater) to the total EEAs. For protease and leucine aminopeptidase, the cell lysis did not increase and even decreased the total EEAs. For alkaline phosphatase, the intracellular enzymes generally had no contribution to the total EEAs. These results showed that passively released intracellular enzymes could substantially increase the total extracellular activities of carbohydrate processing enzymes, which should be considered in building the link between the EEAs and organic carbon cycle in the ocean.

Microbial community respiration kinetics and their dynamics in coastal seawater

Oxygen (O2) concentrations in coastal seawater have been declining for decades and models predict continued deoxygenation into the future. As O2 declines, metabolic energy use is progressively channelled from higher trophic levels into microbial community respiration, which in turn influences coastal ecology and biogeochemistry. Despite its critical role in deoxygenation and ecosystem functioning, the kinetics of microbial respiration at low O2 concentrations in coastal seawater remain uncertain and are mostly modeled based on parameters derived from laboratory cultures and a limited number of environmental observations. To explore microbial responses to declining O2, we measured respiration kinetics in coastal microbial communities in Hong Kong over the course of an entire year. We found the mean maximum respiration rate (Vmax) ranged between 560 ± 280 and 5930 ± 800 nmol O2 L−1 h−1, with apparent half-saturation constants (Km) for O2 uptake of between 50 ± 40 and 310 ± 260 nmol O2 L−1. These kinetic parameters vary seasonally in association with shifts in microbial community composition that were linked to nutrient availability, temperature, and biological productivity. In general, coastal communities in Hong Kong exhibited low affinities for O2, yet communities in the dry season had higher affinities, which may play a key role in shaping the relationship between community size, biomass, and O2 consumption rates through respiration. Overall, parameters derived from these experiments can be employed in models to predict the expansion of deoxygenated waters and associated effects on coastal ecology and biogeochemistry.

Natural light driven plastic leaching effects on carbon chemistry in the tropical coastal waters of eastern Arabian sea: An experimental study

This study examined the effects of solar light driven plastic degradation on carbon chemistry in the coastal waters of eastern Arabian Sea along the west coast of India. The research was conducted through experimental incubations exposed to natural sunlight at multiple locations between December 2023–February 2024. Photodegradation induced a significant pH decrease (up to 0.38 ± 0.02) between controls and plastic incubations ranging from 8.17 ± 0.01 to 7.54 ± 0.02 with the highest variation in the Mumbai coast ranging from 8.13 ± 0.01 to 7.75 ± 0.03. pH variations are primarily caused by the leaching of organic acids and CO2 release during solar irradiated incubation. Plastic leaching due to natural light irradiation and subsequent changes in the water chemistry is of prime significance with dissolved organic carbon (DOC) leaching of 0.002–0.03% of plastic weight into the coastal waters. Our estimations suggest 15–75 metric tonnes (MT) of DOC release per year by plastic pollution in the eastern Arabian Sea coastal waters. Further, the fluorescent dissolved organic matter (FDOM) fragmentation, a part of DOC, may act as an organic source of synthetic contaminants and would promote heterotrophic microbial action in the coastal waters. Photodegradation of plastic and the interaction of natural DOC and plastic-derived DOC resulted in longer wavelengths FDOM, which may affect the penetration of photosynthetically active radiation in the water column, thereby impacting primary production. Finally, future research work focussing on the role of plastic pollution in coastal ocean acidification and vice-versa is essential and will be increasingly intense in the upcoming decades.

Congregibacter variabilis sp. nov. and Congregibacter brevis sp. nov. Within the OM60/NOR5 Clade, Isolated from Seawater, and Emended Description of the Genus Congregibacter.

Two Gram-stain-negative, aerobic, motile by means of flagella, short rod-shaped bacterial strains, designated IMCC43200T and IMCC45268T, were isolated from coastal seawater samples collected from the South Sea of Korea. Strains IMCC43200T and IMCC45268T shared 98.6% 16S rRNA gene sequence similarity and were closely related to Congregibacter litoralis KT71T (98.8% and 98.7%, respectively). Complete whole-genome sequences of IMCC43200T and IMCC45268T were 3.93 and 3.86 Mb in size with DNA G + C contents of 54.8% and 54.2%, respectively. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the two strains were 74.5% and 23.4%, respectively, revealing that they are independent species. The two strains showed ANI values of ≤ 75.8% and dDDH values of ≤ 23.0% to the type and only species of the genus Congregibacter (C. litoralis), indicating that each strain represents a novel species. Both strains contained summed feature 3 (comprising C16:1 ω6c and/or C16:1 ω7c) and summed feature 8 (comprising C18:1 ω6c and/or C18:1 ω7c) as major fatty acid constituents. The predominant isoprenoid quinone detected in both strains was ubiquinone-8 (Q-8). The major polar lipids of the two strains were phosphatidylethanolamine, phosphatidylglycerol, phospholipids, and aminolipids. Based on the phylogenetic, genomic, and phenotypic characterization, strains IMCC43200T and IMCC45268T were considered to represent two novel species within the genus Congregibacter, for which the names Congregibacter variabilis sp. nov. and Congregibacter brevis sp. nov. are proposed with IMCC43200T (= KCTC 8133T = NBRC 116295T = CCTCC AB 2023139T) and IMCC45268T (= KCTC 92921T = NBRC 116135T) as the type strains, respectively.

Coastal water quality dynamics of the Red Sea, southeast coast of Egypt using GeoAI and ChatGPT

The Red Sea coastal environment of Halayeb and Shalateen area is renowned for its abundant marine flora and fauna. It also holds significant economic and cultural importance for local communities. However, this region is currently confronted with various challenges, including climate change and habitat destruction. To effectively address and mitigate these issues, advanced technologies that offer a holistic understanding of the area's environmental conditions are required. This paper applies the integration of Geospatial Artificial Intelligence (GeoAI) and ChatGPT to study the Red Sea Coastal water quality dynamics of Halayeb and Shalateen Area. Landsat imagery and Copernicus Marine Service were used to retrieve area boundaries and monitor the physicochemical characteristics of the coastal water respectively. ChatGPT was utilized to generate Python code that facilitates the creation of optimal distribution maps for each physical and chemical property criterion. The Python codes were incorporated into the Python program within the ArcGIS 10.7.1 and executed to generate the desired maps representing the dynamics of physical and chemical properties. It was found an observed fluctuation in chemical properties next to the coastline around the mouth of two main wadies; Wadi Hudain, and Wadi Da'eb. The degree of stability increased away from the coast toward the deep water. That proved the effect of the runoff on the seawater, as the runoff plays an essential role in the water state, especially in such semi-closed water bodies like the Red Sea where the flashfloods are the main source that can enrich water with sediment and nutrients. The state of seawater in terms of physical properties was not characterized by a specific pattern. The distribution of physical parameters in the Red Sea is influenced by factors such as regional climate variations, monsoonal winds, and local topography. This paper serves as a stepping stone for future research endeavors, exploring the full potential of this integrated approach. It can be concluded that the fusion of GeoAI and ChatGPT technologies has the potential to revolutionize our approach to studying and managing the coastal environment.

Plutonium in the coastal seawater around Chinese nuclear power plants: Sources, distribution, and environmental implications

Coastal surface seawater samples within 30 km around ten Chinese nuclear power plants (NPPs) were systematically investigated. The 239+240Pu activity concentration in the samples varied from 0.226 mBq/m3 to 3.098 mBq/m3, meanwhile the 240Pu/239Pu atom ratios ranged from 0.151 to 0.353. Besides, the Pacific Proving Ground (PPG) close-in fallout and the global fallout were recognized as two primary sources of Pu in these samples. The 239+240Pu activity concentration as well as the PPG contribution showed similar trends as the Kuroshio intrusion path and the coastal currents in the China Seas, illustrating long-range transport and consuming of PPG derived Pu in the coastal China Seas. Moreover, accumulation of PPG sourced Pu in the Beibu Gulf were observed and was attributed to the continuous invasion of the high isotopic Pu that remobilized from the South China Sea (SCS).

Variability in Paralytic Shellfish Toxin Profiles and Dinoflagellate Diversity in Mussels and Seawater Collected during Spring in Korean Coastal Seawater.

Paralytic shellfish toxins (PSTs) are potent neurotoxins produced by certain microalgae, particularly dinoflagellates, and they can accumulate in shellfish in coastal seawater and thus pose significant health risks to humans. To explore the relationship between toxicity and PST profiles in seawater and mussels, the spatiotemporal variations in PST concentrations and profiles were investigated along the southern coast of Korea under peak PST levels during spring. Seawater and mussel samples were collected biweekly from multiple stations, and the toxin concentrations in the samples were measured. Moreover, the dinoflagellate community composition was analyzed using next-generation sequencing to identify potential PST-producing species. The PST concentrations and toxin profiles showed substantial spatiotemporal variability, with GTX1 and GTX4 representing the dominant toxins in both samples, and C1/2 tending to be higher in seawater. Alexandrium species were identified as the primary sources of PSTs. Environmental factors such as water temperature and salinity influenced PST production. This study demonstrates that variability in the amount and composition of PSTs is due to intricate ecological interactions. To mitigate shellfish poisoning, continuous monitoring must be conducted to gain a deeper understanding of these interactions.

Microbial communities on microplastics from seawater and mussels: Insights from the northern Adriatic Sea

Microplastics, synthetic solid particles of different sizes (< 5 mm), pose a major challenge to marine ecosystems. Introducing microplastics into the marine environment leads to the formation of complex microbial communities, a topic of growing interest in environmental research. For this study, we selected an area in the northern Adriatic Sea, less affected by human activities, to understand how pristine environmental conditions influence microbial colonization of microplastics. Samples of coastal seawater and Mediterranean mussels (Mytilus galloprovincialis) were collected in a mussel farm near Debeli rtič of the Slovenian coast. Microplastics were isolated, visually and chemically analyzed and DNA was extracted for metagenomics. In the marine water column, 12.7 microplastics per m3 water column and 0.58 microplastics per individual mussel were found. Sufficient DNA was available to analyze six particles, five originating from seawater, and one from a mussel. This was the first-ever sequenced microplastic particle from a mussel. Genera of Pseudomonas and Serratia were identified in all samples. In one of the samples, the most abundant was a marine genus Pseudoalteromonas, while in another sample Campylobacter was present with >30 % abundance. The microbiomes of the mussel- and seawater-isolated particles were similar, suggesting a common microbial colonization pattern, which may have implications for the transfer of microplastic-associated microbes, including potential pathogens, through the food web to the consumers. Microplastic pollution is a complex issue requiring further research, especially regarding microbial biofilms, pathogen colonization and the potential of pathogen transmission via microplastic particles. Our findings enhance the understanding of microplastic pollution in the Adriatic Sea and stress the necessity for comprehensive strategies to mitigate the impact on marine ecosystems.

Peculiarities of seasonal dynamics of net primary production and its microzooplankton grazing in the coastal waters of the Black Sea (Sevastopol region)

The studies of net primary production (NPP) seasonal dynamics, its microzooplankton grazing were conducted at two stations in the western Black Sea coastal waters near Sevastopol during a period from January 2020 to December 2022. Each year, one maximum of the phytoplankton NPP (280–820 mg C·m-3·day-1) was observed in July, when the water temperature ranged from 22 to 25 °C, and solar radiation intensity was 48–50 E·m-2·day-1. Large diatoms and dinoflagellates played a key role in its formation. At this time, the values of the net phytoplankton growth rate were 0.3–1.0 day-1, and the relative share of primary production consumed by microzooplankton (g/m) did not exceed 26%. In December – February, when the water temperature was 8.0–13.5 °C and the intensity of solar radiation was 10–15 E·m-2·day-1, the NPP decreased to a minimum (4–38 mg C·m-3·day-1). Under these conditions, the net phytoplankton growth rate decreased to 0–0.40 day-1, and g/m was 15–100%. For three years at station 2, the contribution of large algae with cell volumes from 4000 to 18000 µm3 in the NPP was significantly higher than at station 1. It was 61.1 % in 2020, 69.7 % in 2021 and 23% in 2022. The consumed NPP for this size group of algae was 54 % in 2020, 68.4 % in 2021 and 47.8 % in 2022.

Deciphering the uranium isotopic signature of coastal water and sediments from Tokyo Bay using a multi-collector inductively coupled plasma mass spectrometer

We have measured 236U/238U and 235U/238U values in JMS-1 (geochemical reference material of Tokyo Bay sediments) and coastal seawater using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) equipped with both the retarding potential quadrupole lens and desolvating nebuliser system. For the accurate measurement of 236U/238U values (e.g., in the range of 10−9), mass spectrometric interferences on 236U isotope from both the peak tailing of 238U and polyatomic ion of 235UH were carefully corrected. With the sequential extraction experiments for JMS-1, whose U isotopic signatures were characteristic of isotopically-depleted U with industrial uses, authigenic U was extracted into a soluble fraction, and lithogenic U and anthropogenic U were gathered in an insoluble fraction. The anthropogenic U is likely to have been provided in insoluble forms and have deposited on the bay floor. Absence in differences of 236U/238U and 235U/238U values for seawater observed between inside and outside Tokyo Bay implies the negligibly small contribution of the anthropogenic U to U in the seawater. The data obtained here demonstrate the effective reduction of the interferences on 236U and the versatility of the isotopic signatures of U as an effective tracer for environmental circulation of U in nature.