Semi-enclosed Bay Research Articles

The reasons for the spatial and media distribution variations of ARGs in a typical semi-enclosed bay

Antibiotic resistance genes (ARGs) are considered a newly emerging contaminant. This study aimed to investigate the spatial and media distribution patterns of ARGs in Jiaozhou Bay, as well as the reasons behind these patterns. The results revealed that aminoglycoside and MLSB resistant genes predominated in all samples, and the relative abundance of ARGs ranging from 10−6 to 10−2, 10−6 to 10−3 and 10−5 to 10−2 copies/16S rRNA in coastal water, bay water, and sediments, respectively. The significant spatial variation of ARGs was explained by the fact that the coastal water was more susceptible to human activities, whereas environmental physicochemical factors played a crucial role in the bay water. The intrinsic reason for the media distribution variation was the different assembly processes in the two media, while the external reason was that the ARGs in the water and sediments were mainly influenced by environmental physicochemical factors and heavy metals, respectively.

Morphometric study and statistical analysis of gephyrocapsids in surface sediments from offshore western Luzon and semi-enclosed bays in the Philippines.

Morphometric study and statistical analysis of gephyrocapsids in surface sediments from offshore western Luzon and semi-enclosed bays in the Philippines.

Circulation and stratification drivers during the summer season in the upwelling bay of Paracas (Peru): A modelling study

The circulation and stratification in the shallow semi-enclosed bay of Paracas located downstream of the main upwelling cell off the Peruvian coast were studied during the summer season using a regional circulation model and in situ observations. A downscaling strategy based on a series of three embedded grids, from 10 km to 500 m resolution in the bay allows to take into account the influence of remote perturbations on the bay dynamics. Debiased surface winds from a high-resolution regional atmospheric model were used to force the model. The shortwave absorption depth was parameterized using satellite measurements of surface chlorophyll.Sensitivity experiments to the model forcing and parameterizations were performed to investigate the impact of the wind diurnal variability, tidal forcing, freshwater discharge from a nearby river and shortwave absorption depth on the bay stratification. Results show that: debiasing the wind intensity reduced the model cold bias in the bay and increase the stratification; a shallow shortwave absorption depth induced a cooling of the subsurface water, increasing the stratification; freshwater discharge from the Pisco river north of the bay increased slightly the stratification in the bay during days of weak wind. The high sensitivity of the bay stratification to the atmospheric forcing calls for the need to use more realistic wind forcing products.The circulation in the bay under strong (>5.5 m s−1) and weak (<3 m s−1) winds was also examined. The summer circulation during strong upwelling-favorable wind conditions was characterized by northward surface currents transporting the bay surface waters outward and subsurface currents transporting cold deeper waters into the bay along its western shore. During weak wind conditions, the current is outward in the bottom layer and a surface southward current related to the poleward undercurrent flowing over the continental slope and shelf transported warm waters into the bay, generating a cyclonic circulation in the bay.

Effects of an Episodic Storm-Induced Flooding Event on the Biogeochemistry of a Shallow, Highly Turbid, Semi-Enclosed Embayment (Laizhou Bay, Bohai Sea)

Episodic storm-induced flooding is becoming more frequent with a warming climate, which may alter the biogeochemical properties and conditions of estuaries. However, the effects of such extreme events on semi-enclosed bay ecosystems have not been fully investigated because of the difficulty in collecting in situ samples. To address this issue, a comparative study was carried out to understand the biogeochemical changes in Laizhou Bay, a shallow, highly turbid, semi-enclosed bay, by coupling satellite data and surface water samplings collected during an episodic flooding event (August 2018) and during a non-flooding period (August 2017). The results showed that the 2018 Shouguang flood delivered large amounts of suspended solids, phosphorus, and organic matter-enriched terrigenous materials into Laizhou Bay and enhanced the offshore expansion of the low-salinity seawater plume and associated nutrient fronts. Water total suspended solid (TSS) particle and chlorophyll a (Chl-a) concentrations increased by 23.79 g/m3 and 0.63 mg/m3, respectively, on average in the freshwater mixing water plume around the Mi River. Episodic flooding is a crucial driver which temporally dominates the spatial patterns of water biogeochemistry. These results are essential to anticipate the ecosystem response of estuarine regions to the high episodic freshwater flow associated with the increasing storms.

Assessment of Microplastics in Green Mussel (Perna viridis) and Surrounding Environments around Sri Racha Bay, Thailand

Microplastic pollution is a common problem in the coastal and marine environment, especially in the transferential process through trophic levels. This study analyzed the characteristics of microplastics in the seawater, sediments, and green mussels (Perna viridis) around Sri Racha Bay, Thailand, during the dry and wet season in 2020. This area is a semi-enclosed bay highly affected by extensive green mussel farms and anthropogenic activities. Qualitative and quantitative analysis of microplastics was undertaken using a stereomicroscope and micro-Fourier transform infrared spectrometer (ATR-μ-FT-IR). During the wet season (July), the average abundance of microplastics was found to be relatively higher in water (2.06 ± 1.78 particles/m3) and sediment (69.35 ± 22.29 items/Kg D.W.) than those found in the dry season (April) (0.85 ± 0.25 items/m3 in water and 48.30 ± 28.17 items/Kg D.W.). Overall, the most abundant microplastic polymers were PE, PP, and poly in water, but PE, nylon, and PP in sediments. In green mussels, microplastic counts were 0.15 ± 0.41 and 0.22 ± 0.57 items/individual in the dry and wet season, respectively, and PET, PP, and nylon were the three most abundant. Some inter-specific differences were found, but no evidence for a sampling sites or seasons was highlighted, although the tendency was higher during the wet season. The excessive riverine freshwater discharge transported terrestrial plastic debris into the estuarine system; hence, higher microplastic contamination in surface seawater and sediment was evidenced. The presence of colorants in organisms revealed an anthropogenic origin through the use of a wide array of applications. This study provides thoughtful insights for coastal area management and food-safety planning.

Influence of a heavy rainfall event on nutrients and phytoplankton dynamics in a well-mixed semi-enclosed bay

With a warming climate, extreme precipitation events are projected to occur more frequently in future, which can lead to sediment and freshwater pulses to coastal waters that quickly affect water quality. Understanding how coastal systems respond to and recover from such acute events is becoming more and more important, particularly true in semi-enclosed bays with weak water exchange and purification capacities, such as Jiaozhou Bay (JZB). Based on the three cruises performed on 17 July, 5 and 22 August 2012, a coupled physical-biological model was used to examine ecosystem responses in JZB to Typhoon Damrey, an extreme precipitation event. In order to study the mechanism behind rainfall-induced changes, three groups of sensitivity experiments were set to furtherly analyze the contributions of rivers and atmospheric deposition, respectively. The results showed that typhoon-induced rainfall provided high concentration of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) to phytoplankton which caused a remarkable chlorophyll-a increase subsequently. During the heavy rainfall event, the nitrogen and phosphorus inputs from river runoff were 1.80 and 2.14 times than that from atmospheric deposition, respectively. River inputs supported 2.14 times the productivity than that supported by atmospheric deposition. Rainfall-induced nutrient input will lead to blooms in coastal areas, especially in semi-enclosed bays. Since increased rainfall would trigger higher river discharge, rivers became the main carriers of nutrients. Atmospheric deposition provided a low-level supply, and it was limited for alleviating phosphorus limitation in semi-enclosed bays. Enhancing ecological monitoring of rivers and atmospheric deposition is urgent and essential to predict the response of ecosystems to extreme rainfall events.

High Throughput Sequencing Reveals Distinct Bacterial Communities and Functional Diversity in Two Typical Coastal Bays

The marine waters in semi-enclosed bays are highly dynamic and strongly influenced by different levels of anthropogenic activity. This study explored the bacterial community composition and diversity in two typical urbanized coastal bay areas (Shenzhen Bay (S) and Dapeng Bay (D)) in Shenzhen, China, based on Illumina NovaSeq sequencing. Seawater analysis showed that coastal area S experienced a higher level of pollution, with higher nutrient concentrations observed. Alpha diversity analysis showed a higher bacterial diversity and richness in coastal area S than D. Taxonomic analysis revealed that the phylum Proteobacteria showed the highest abundance in all samples. Other dominant phyla were Firmicutes, Cyanobacteria, Tenericutes, and Actinobacteria. The bacterial community compositions were significantly different between the two coastal areas. A significant community difference was also found between the sampling sites of coastal area S. However, the difference between sampling sites in coastal area D was not significant. Physicochemical factors showed a more significant effect on bacterial community composition than nutrients. Pearson correlation tests and Network analysis further confirmed that salinity/conductivity, pH, and nitrate were the key factors driving the community difference. PICRUSt analysis revealed a higher degree of functional pathways in coastal area S relating to carbohydrate metabolism, membrane transport, and xenobiotics biodegradation. Our results provide in-depth insights into the bacterial community compositions in typical polluted coastal bays. They may provide information on underlying factors of the assembly process in microbial communities in the coastal zone.

210Po and 210Pb as tracers for particle cycling in a shallow semi-enclosed bay of Taiwan Strait

Naturally-occurring 210Po and 210Pb are good tracers for particle cycling in the estuarine and coastal environment. Activities of 210Po and 210Pb were measured in samples of bulk (wet + dry) atmospheric deposition, river water and surface seawater collected in the Zhangjiang Estuary-Dongshan Bay to investigate the geochemical scavenging rates (or residence times) of these particle-reactive nuclides. The spatial distribution of 210Po and 210Pb were strongly influenced by suspended particulate matter (SPM) concentrations and in almost all stations, 210Po and 210Pb were mainly in particulate form (51.7%–92.2% of the total for 210Po and from 44.3% to 90.3% for 210Pb). Due to the very high SPM concentration, enhanced scavenging of 210Po and 210Pb was observed in the maximum turbidity zone of Zhangjiang River, with a marked decrease of dissolved nuclides’ activities. We built a mass balance model and we found out that atmospheric inputs are the major source of these radionuclides comparing with other sources (e.g., river inputs or ingrowth production) in the study area. Residence times of 210Pb were calculated to be 2.2–9.8 and 0.5–8.9 days for dissolved and particulate 210Pb, respectively. And residence times of dissolved and particulate 210Po were 6.3–31.7 and 2.2–13.9 days, respectively. In the turbidity zone, we found an unexpected result that particulate 210Po and 210Pb had the longest residence times (about two weeks), suggesting that SPMs in the turbidity zone would not be easy to sink to the sea floor. We also found that different SPMs showed significantly different 210Po/210Pb activity ratios, which increased in the following order: atmospheric deposition in dry season < SPMs in river < SPMs in the Zhangjiang Eastuary-Dongshan Bay < biogenic particles (including detritus, fecal pellets, cells of phytoplankton and zooplankton). This phenomenon implied that 210Po/210Pb activity ratio in the particles has the potential application in distinguishing SPM sources in the coastal seas.

Transboundary microplastic pollution in Xiamen Bay and adjacent Jiulong River estuary after the outbreak of COVID-19

Land-based transport from nearshore areas is a key pathway of microplastic (MP) pollution in the oceans. Therefore, transport, fate, and intervention on MPs necessitate an investigation of MP contamination in coastal regions. Here, MP pollution in the surface waters of Xiamen Bay and Jiulong River estuary was evaluated in 2021 after the outbreak of COVID-19. The abundance of MPs in Xiamen Bay ranged from 0.20 to 5.79 items m−3 with an average of 1.03 items m−3, whereas that in the Jiulong River estuary spanned from 0.55 to 2.11 items m−3 with a mean of 1.30 items m−3. A yearly decreasing trend in the abundance of MPs in surface waters in both regions was observed. The particle sizes of MPs were concentrated in the range of 2.50–5.00 mm, and the colors were mainly white, transparent, and green. The micro-Raman spectroscopic results showed that MP polymer types were predominantly polyethylene, polypropylene, and polystyrene. A lower abundance of MPs in Xiamen Bay with no obvious pattern was observed, while that in the Jiulong River estuary showed a wavelike distribution from upstream to downstream. Ecological risk assessment of MP pollution in surface waters of two regions was performed using the pollution load index (PLI), giving the risk level in descending order: wastewater discharge area > aquaculture area > sloughs > estuary mouth > estuarine rivers > shipping lane. The average risk level of Xiamen Bay (I) was lower than that in Jiulong River estuary (II). The MP pollution in the Jiulong River estuary appeared heavier than that in Xiamen Bay, which may be due to the combined effects of COVID-19 and marine governance. This study provided insights into the prevention and management of MP pollution in nearshore semi-enclosed bays.

Assessing the sources and dynamics of organic matter in a high human impact bay in the northern Beibu Gulf: Insights from stable isotopes and optical properties

Severe human activities in coastal areas have greatly impacted the sources and biogeochemical behaviors of organic matter (OM), including particulate OM (POM) and dissolved OM (DOM). However, few studies have incorporated the indices of POM and DOM to address this issue. Here, a dataset of the combination of stable isotopes of carbon and nitrogen in POM and the optical properties of DOM was presented in Xi Bay, a semi-enclosed bay with a highly developing industrial port in Beibu Gulf, South China, to reveal the origin, distribution, and fate of OM during the rainy season. In the upper bay, depleted δ13C suggested that particulate organic carbon (POC) mainly originated from terrestrial sources. However, the negative relationship between chromophoric DOM (CDOM) and particulate nitrogen (PN) suggested that bacterial-mediated decomposition of POM may be the primary source of CDOM. The negative correlation between humic-like fluorescent components (C1 and C2) and salinity suggested that those two components were mainly affected by terrestrial input. The significant correlation between the protein-like component (C3) and Chl a suggested that C3 was mainly derived from phytoplankton production in the upper bay. In the lower bay, the increase of δ13C values indicated an increased contribution of marine POC. The high levels of CDOM may be due to the decomposition of marine (fresh) POM. However, the low levels of C1 and C2 might be affected by dilution with seawater, and the increased levels of the protein-like C3 were due to enhanced primary production. In addition, the enhancement of δ15N values in both the upper and lower bays indicated serious nitrogen pollution in the bay. This study highlights that biological production fueled by excess nutrients is the dominant OM dynamic process in the bay with high human impact in Beibu Gulf.

Co-occurrence of pectenotoxins and Dinophysis miles in an Indonesian semi-enclosed bay

The study aims to unravel the variability of Dinophysis spp. and their alleged toxins in conjunction with environmental drivers in Ambon Bay. Phytoplankton samples, lipophilic toxins and physiochemical water properties were analysed during a 1.5-year period. Three Dinophysis species (D. miles, D. caudata, and D. acuminata) were found in plankton samples, of which D. miles was the most abundant and persistently occurring species. Pectenotoxin-2 (PTX2) and its secoacid (PTX2sa) were detected throughout, and PTX2sa levels strongly correlated with D. miles cell abundance. The toxin showed a positive correlation with temperature, which may suggest that D. miles cells contain rather constant PTX2sa during warmer months. Dissolved nitrate concentrations were found to play a major role in regulating cell abundances and toxin levels. This study adds adequate information regarding marine biotoxins and potentially toxic species for future Harmful Algal Bloom management in Ambon and Indonesia at large.

Seasonal variation, virulence gene and antibiotic resistance of Vibrio in a semi-enclosed bay with mariculture (Dongshan Bay, Southern China).

In this study, the virulence genes, antibiotic resistance of culturable Vibrio and the environmental factors affecting Vibrio abundance were analyzed in four seasons in DongShan Bay with different intensity of aquaculture practice. A total of 253 bacteria isolates were obtained, of which 177 Vibrio strains belonged to 26 species. Annual Vibrio abundance in this region ranged from 20 to 11,600CFUmL-1 and the most significant positive correlation occurred with temperature. Detection of 9 different Vibrio virulence genes revealed that most isolates contained atypical virulence genes in addition to the typical ones. In particular, virulence genes of hemolysin such as tdh, trh, and hlyA (6.32%, 15.52%, and 11.30%) showed different degrees of horizontal gene transfer (HGT). In our antibiotic resistance test, the multiple antibiotic resistance (MAR) index of the isolates ranged from 0.01 to 0.03 in different seasons, and three MAR Vibrio strains were detected. Overall, our study sheds new light on the spatial distribution patterns and the occurrence of virulence genes and antibiotics resistance Vibrio isolated from a subtropical bay with intensive aquaculture. Our study provides a suitable microbial quality surveillance in a mariculture impacted coastal environment. It will help to establish effective disease prevention measures in this area and provide useful guidance and support for formulating local antibiotics use policies.

Environmental processes and fate of PAHs at a shallow and enclosed bay: West Nanao Bay, Noto Peninsula, Japan

From August 2019 to August 2020, particulate and dissolved polycyclic aromatic hydrocarbons concentrations (PAHs) were analyzed in the water body of West Nanao Bay, Japan, to determinate their levels, environmental pathways, and ecological risks at this remote but shallow and semi-enclosed bay. The 14 targeted PAHs were analyzed by high performance liquid chromatography-fluorescence detector. Even when water column stratifies, the summatory of 14 targeted dissolved PAHs did not follow significantly change with depth. Results agreed with our previous findings in the surface distribution at the bay and can be attributed to long retention time of the water mass of the semi-enclosed bay. Suspended solids start precipitating according to their size; with biggest particles rapidly settling in the proximities of river mouths. Partition coefficients (Kp) varied from 103 to 107, according to molecular weights. In general, highest Kp were found in the nepheloid layer. The risk quotients, RQ∑14 PAHs (NCs) (1.04-174.08), indicated that PAHs represented a very low to low environmental risks.

Analysis of the Ecosystem Characteristics and Ecological Carrying Capacity of the Main Commercial Fish in the Artificial Reef Ecosystem in Laizhou Bay Using the Ecopath Model

In this study, we constructed an Ecopath model of the artificial reef ecosystem in Laizhou Bay, with special emphasis on the stock enhancement opportunities. Laizhou Bay is the largest semi-enclosed bay in the Bohai Sea, China, where multiple factors, especially overfishing, have led to the decline of many commercial marine fish stocks. Artificial oyster reefs were developed in 2011 in this region, providing shelter, feeding, and breeding sites for marine organisms. Additionally, stock enhancement by release can be used to replenish fishery species resources. Ad hoc stock enhancement, however, can fail to bring economic benefits and may impact ecosystem stability. Therefore, we estimated the ecological carrying capacity of the three main economic fish species in Laizhou Bay, including black rockfish (Sebastes schlegelii), fat greening (Hexagrammos otakii), and Chinese seabass (Lateolabrax maculatus) before release to ensure the sustainable use of fishery resources. The Ecopath model in Laizhou Bay was divided into 17 functional groups based on commercial relevance, dietary similarity, and habitat needs of the species present in the area. The ecological parameters, such as the ratio of total primary productivity to total respiration (1.205), connectance index (0.207), and system omnivory index (0.090) indicated that the artificial reef ecosystem in Laizhou Bay has a relatively simple food web structure. The ecological carrying capacities of S. schlegelii, H. otakii, and L. maculatus were assessed at 0.4676 t/km2, 0.5472 t/km2, and 0.3275 t/km2, respectively. This study provides a reference for the formulation of fishery strategies to maintain ecosystem stability and biodiversity and to maximize fishery returns and sustainability in Laizhou Bay.

Seasonal variation and ecological risk assessment of Pharmaceuticals and Personal Care Products (PPCPs) in a typical semi-enclosed bay — The Bohai Bay in northern China

The Bohai Bay as a typical semi-enclosed bay in northern China with poor water exchange capacity and significant coastal urbanization, is greatly influenced by land-based inputs and human activities. As a class of pseudo-persistent organic pollutants, the spatial and temporal distribution of Pharmaceuticals and Personal Care Products (PPCPs) is particularly important to the ecological environment, and it will be imperfect to assess the ecological risk of PPCPs for the lack of systematic investigation of their distribution in different season. 14 typical PPCPs were selected to analyze the spatial and temporal distribution in the Bohai Bay by combining online solid-phase extraction (SPE) and HPLC-MS/MS techniques in this study, and their ecological risks to aquatic organisms were assessed by risk quotients (RQs) and concentration addition (CA) model. It was found that PPCPs widely presented in the Bohai Bay with significant differences of spatial and seasonal distribution. The concentrations of ∑PPCPs were higher in autumn than in summer. The distribution of individual pollutants also showed significant seasonal differences. The high values were mainly distributed in estuaries and near-shore outfalls. Mariculture activities in the northern part of the Bohai Bay made a greater contribution to the input of PPCPs. Caffeine, florfenicol, enrofloxacin and norfloxacin were the main pollutants in the Bohai Bay, with detection frequencies exceeding 80 %. The ecological risk of PPCPs to algae was significantly higher than that to invertebrates and fish. CA model indicated that the potential mixture risk of total PPCPs was not negligible, with 34 % and 88 % of stations having mixture risk in summer and autumn, respectively. The temporary stagnation of productive life caused by Covid-19 weakened the input of PPCPs to the Bohai Bay, reducing the cumulative effects of the pollutants. This study was the first full-coverage investigation of PPCPs in the Bohai Bay for different seasons, providing an important basis for the ecological risk assessment and pollution prevention of PPCPs in the bay.

Impacts of hypoxia on the mesozooplankton community structure in a semi-enclosed bay

Gamak Bay is frequently affected by hypoxia in summer. Therefore, this study aimed to examine the effect of hypoxia on the mesozooplankton community of this region. Mesozooplankton samples were obtained biweekly (28 times) at a hypoxic station (inner bay) and a normoxic station (middle bay) using a conical net (mesh size 200 μm; mouth diameter 30 cm) from April 2020 to April 2021. In the inner bay, hypoxia was observed a total of five times between early June and late September, whereas no instances of hypoxia were detected in the middle bay. During the hypoxic period, mesozooplankton abundance was higher in the inner bay than the middle bay (p &amp;lt; 0.05). During the normoxic period, there was no difference between the inner bay and the middle bay (p &amp;gt; 0.05). The dominant species in the hypoxic period were three species of cladocerans (Pleopis polyphemoides, Pseudoevadne tergestina, Penilia avirostris) and the copepod Acartia sinjiensis. The abundance of cladocerans was higher in the inner bay, and that of A. sinjiensis was higher in the middle bay (p &amp;lt; 0.05). In addition to water temperature, salinity, and size-fractionated Chl-a concentration, mesozooplankton abundance was also significantly correlated with the bottom DO concentration. Collectively, our findings suggest that hypoxia can affect mesozooplankton abundance and occurrence times.

Phthalate esters and plastic debris abundance in the Red Sea and Sharm Obhur and their ecological risk level

The abundance of plastic debris (PDs) and its correlation with phthalic acid esters (PAEs), a class of pollutants associated with plastics, is not well understood, although PDs have been reported in relation to the release and distribution of aquatic pollutants such as PAEs. Few studies have linked the distribution of these pollutants in seawater. The current study examined the abundance and relationship of PDs and PAEs in seawater from Sharm Obhur and the Red Sea. Estimates were also made of their ecological impacts. Sharm Obhur is a semi-enclosed bay on the eastern shore of the Red Sea, near Jeddah, Saudi Arabia, and is heavily impacted by human activities. Contaminants from Sharm Obhur may be transported into the deep waters of the Red Sea by the subsurface outflow. The PAEs concentrations in the study area ranged from 0.8 to 1224 ng/L. Among the six PAEs studied, diethyl phthalate (DEP) (22–1124 ng/L), di-n-butyl phthalate (DBP) (9–346 ng/L) and di (2-ethylhexyl) phthalate (DEHP) (62–640 ng/L) were the predominant additives detected across all the sampling sits. Whereas the other PAEs, dimethyl phthalate (DMP) (5–76 ng/L), benzyl butyl phthalate (BBP) (4–25 ng/L) and di-n-octyl phthalate DnOp (0.5–80 ng/L) were generally lower in most samples. The sum of the six analyzed PAEs (∑6 PAEs) was lower at Sharm Obhur (587 ± 82 ng/L) and in the Red Sea shelf (677 ± 182 ng/L) compared to the Red Sea shelf break (1266 ± 354 ng/L). This suggests that degradation and adsorption of PAEs were higher in Sharm Obhur and on the shelf than on the shelf break. In contrast, there was no difference in the abundance of PDs between Sharm Obhur (0.04 ± 0.02 PDs/m3), Red Sea shelf (0.05 ± 0.02 PDs/m3) and in the Red Sea shelf break (0.03 ± 0.1 PDs/m3). Polyethylene (32%) and polypropylene (8%) were dominant, mostly smaller than 5 mm2 (78%), with the majority consisting of white (52%) and black (24%) fragments (39%), fibers (35%) and films (24%). A positive correlation between PAE concentration and abundance of PDs, suggests either a common source or a causal link through leaching. The ecological risk of ∑4PAEs (DMP, DEP, DBP and DEHP) ranged from (0.20–0.78), indicating a low to moderate risk for the Red Sea. The pollution index of PDs ranged from (0.14–0.36), showing that the Sharm Obhur and both sites of Red Sea suffered relatively low pollution.

Size-fractionated microbiome observed during an eight-month long sampling in Jiaozhou Bay and the Yellow Sea

Jiaozhou Bay is a typical semi-enclosed bay with a temperate climate imposed by strong anthropogenic influence. To investigate microbial biodiversity and ecosystem services in this highly dynamic coastal environment, we conducted a monthly microbial survey spanning eight months at two stations in the bay and the open Yellow Sea starting in April 2015. This report provides a comprehensive inventory of amplicon sequences and environmental microbial genomes from this survey. In total, 2,543 amplicon sequence variants were obtained with monthly relative abundance profiles in three size fractions (>2.7 μm, 2.7–0.7 μm, and 0.7–0.22 μm). Shotgun metagenomes yielded 915 high-quality metagenome-assembled genomes with ≥50% completeness and ≤5% contamination. These environmental genomes comprise 27 bacterial and 5 archaeal phyla. We expect this comprehensive dataset will facilitate a better understanding of coastal microbial ecology.

Distinct distribution patterns of planktonic ciliate communities along environmental gradients in a semi-enclosed bay

Jiaozhou Bay is a representative temperate coastal ecosystem and connects with the Yellow Sea by a narrow mouth. The eastern part of the Bay is more polluted than the western and outer parts due to the combined effects of urban sewage and weak water exchange between different water masses. However, the previous results from microscopy analyses did not show any distinct distribution pattern of planktonic ciliates, which are generally considered good bioindicators along environmental gradients. We hypothesize that ciliates may respond to environmental stress by regulating the community of rare taxa, which was not uncovered by morphological methods. The diversity and distribution patterns of planktonic ciliate communities were investigated through high-throughput DNA sequencing from 13 stations in the eastern, western and outer parts of Jiaozhou Bay. The alpha diversity indices showed an increasing trend from the east Bay to the west Bay to the outer Bay. Significant differences in planktonic ciliate communities from different zones of the Bay were mainly attributed to rare rather than abundant taxa. Correlation network analysis revealed that the rare taxa generally have positive correlations with other rare ones, while more negative correlations were found among abundant taxa. We further revealed the distributions of three dominant genera (Stenosemella, Tintinnopsis, and Strombidium) were significantly correlated with environmental variables, suggesting that they might be used as ecological indicators. Our results elucidate the bioindicator potential of ciliate along environmental gradients in a semi-enclosed bay.

137Cs Sediment Profiles as a Tracer of Marine Sedimentation Processes in a Semi-Enclosed Bay Affected by Anthropogenic Releases—Example of Kaštela Bay (Adriatic Sea, Croatia)

Kaštela Bay was taken as a model to study sedimentation processes using the vertical sediment profiles of 137Cs massic activities. The aim was to distinguish the sedimentation conditions in different parts of the Bay and to partly determine the pathways of terrigenous input into the Bay. The purpose was to demonstrate that 137Cs profiles are applicable in differentiating sedimentation processes. It was found that mostly continuous, undisturbed sedimentation takes place in the central and south parts of the Bay; the sedimentation conditions in the west part of the Bay are more complicated. The west part is characterised by the extremely slow sedimentation of the coarse-grained sediment or even by erosion and selective resuspension of the fine-grained particles followed by resedimentation in other parts of the Bay. It was also observed that the upper 10 cm of the sediment is the most exposed to homogenisation. The strong influence of the Jadro River and anthropogenic activities in the east part of the Bay are reflected in the higher 137Cs activities, strong sediment mixing, and increased sediment input. This study shows that the 137Cs profiles can provide comprehensive insights for the whole study region when a sophisticated sampling layout is deployed. The results of the study are applicable to other aquatic environments with comparable processes and sedimentary environments.