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- Microbial Diversity of Deep-sea Sediments from Three Newly Discovered
Hydrothermal Vent Fields in the Central Indian Ridge-
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Abstract: Abstract Since the discovery of hydrothermal vents in the late 1970s, deep-sea hydrothermal vent fields have attracted great attention as biological hotspots. However, compared with other ocean ridges, the structure and function of microbial communities inhabiting vent fields in the Central Indian ridge (CIR) remain understudied. Here, we provide for the first time 16S rRNA gene-based comparative metagenomic analysis of the sediment-associated microbial communities from three newly discovered vent fields in the CIR. Sediment samples collected in the Invent B, Invent E and Onnuri vent fields varied in geochemical properties, elemental concentrations and associated microbial communities. Proteobacteria (Gammaproteobacteria) was the dominant phylum in Invent B and Onnuri vent fields. In contrast, Invent E mainly consisted of Chloroflexi and Euryarchaeota. Predicted functional profiling revealed that the microbial communities in the three vents are dominated by chemoheterotrophic functions. In addition, microbial communities capable of respiration of sulfur compounds, nitrification, nitrite oxidation, methylotrophy, and methanotropy were found to be the main chemolithoautotrophs. Compared to other vent fields, Invent E showed a predominance of archaeal methanogens suggesting it exhibits slightly different geochemistry. Multivariate analysis indicated that the biogeochemical and trace metal differences are reflected in the sediment microbial compositions of the three vent fields. This study expands our current understanding of the microbial community structure and potential ecological functions of the newly discovered hydrothermal vent fields in the CIR.
PubDate: 2023-03-09
- A Data-Driven Binary-Regression Framework for Rapid Screening of Marine
Fuel Oil-
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Abstract: Abstract Despite the decreases in the number of oil spill cases over the years, marine oil pollution caused by indirect transfer of oil combustion emissions has drastically escalated with global shipping activities. As a response, a global initiative to control ship emissions, particularly focusing on sulfur oxide, was established by the International Maritime Organization. As part of the enforcement plan, time and resource consuming chemical analysis methods for the inspection of fuel oil have become essential to ensure that vessels comply with the regulation. In order to increase the efficiency of chemical analysis, ultraviolet–visible spectroscopy coupled with chemometrics was developed for the characterization of oil. This study aimed to develop a rapid yet accurate oil physicochemical property screening method by combining simplified spectrometry techniques coupled with chemometrics. A partial least squares model for physicochemical properties such as sulfur content, viscosity, and saturate, aromatic, as well as polar fraction, was calibrated with 330 spectra and validated using 100 spectra. Prediction models were highly accurate with R2 and root mean square error of prediction (RMSEP) values ranging from 0.80–0.96 and 0.10–3.08, respectively. With an R2 value of 0.86, high correlations amongst predicted variables further validated the robustness of models. A quantitative comparison between the time needed for oil characterization through data-driven binary regressions and standardized chemical analysis methods indicated that data-driven binary regressions are 94% more efficient than standardized chemical analysis methods. This study demonstrated that simplified spectroscopy techniques can be powerful tools for rapid screening of environmental pollution when coupled with chemometrics.
PubDate: 2023-02-15
- Biometrical Variation of Posidonia oceanica with Different Bottom Types
Along the Entire Turkish Mediterranean Coast-
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Abstract: Abstract The biometrical dynamics of Posidonia oceanica were studied with regard to variation and its depthwise extension with four major bottom types along the entire Turkish Mediterranean coasts in winter and summer during 2019. The bottom type which mainly consisted of rock, matte (hard bottom), sand, and mud (soft bottom) was a key determinant for biometrical (density and morphometric) changes which were more prominent in summer. The upper and lower limits of vertical depthwise extension of the meadows were restricted by the zonal distribution of the hard bottom. The limits were not restricted on the soft bottom. However, some large areas of the soft bottoms were devoid of the meadows depending on the existence of mobile substrate affected by the high dynamic of water movement. The density variables were higher on hard bottoms than on the soft bottoms; the inter-nodal distance was longer on matte than on rock, sand, and mud, in contrast to leaf biomass. Mud had the lowest number of leaves per shoot and shoot density, whereas rock had the highest number. The shortest rhizome was measured on the rock, while the longest rhizome was measured on matte, which also had the longest leaves. The soft bottoms had wider leaves than the hard bottoms had. Besides the seasonal and depthwise differences in the biometrics, the biometrics were separately assembled between rock and mud. Contrary to the morphometric variables, the density biometrics decreased linearly from the hard bottom to the soft bottom.
PubDate: 2023-02-06
- Fluid Mud Dynamics and Its Correlation to Hydrodynamics in Jiaojiang River
Estuary, China-
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Abstract: Abstract The Jiaojiang Estuary is a macro-tidal estuary with high turbidity and funnel-shaped geomorphology. Estuarine geomorphology and shipping are highly affected by sediments and heavy coastal engineering. Based on observed data and numerical simulation results, we studied the characteristics of the suspended sediments and fluid mud in the estuary. By considering two-way coupling of water–sediment density and the process of fine sediment flocculation, a three-dimensional sediment model of the Jiaojiang Estuary was established and effectively calibrated using the measured data on tides, currents, and suspended sediment concentration (SSC). Field data analysis indicated that SSC and sediment transport rate in both the main tidal channel and shoals were positively correlated with the flow velocity in the low-frequency part during both the spring and neap tides. The model results revealed that the net sediment flux is controlled by advection and moves landward upstream of the main tidal channel. Fluid mud is formed near Haimen station, with tides influencing the spatial and temporal variations in its thickness and speed. Sediment is actively exchanged among fluid mud-water-seabed, with sink and source processes dominating near the bay mouth and the Haimen station, respectively. Sediments weaken the seaward residual currents slightly by changing their viscosity and the von Karman constant, and the stratification process is affected by changes in water density. The findings of this study provide a foundation for the study of material transportation in an estuarine ecosystem.
PubDate: 2023-02-06
- A Biological Indication of Vertical Mixing of the Yellow Sea Bottom Cold
Water-
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Abstract: Abstract The identities and origins of water masses in mixed seawater can be effectively traced by comprehensively analyzing physicochemical and biological data. In this study, distribution of an indicator species of the Yellow Sea Bottom Cold Water, Tintinnidium primitivum, was monitored to trace vertical mixing across seasons along the 35 °N line from 2019 to 2022. A bottom-oriented distribution was observed in every season except for winter. Winter vertical mixing was supported by water temperature and salinity profiles and the homogenous distribution of T. primitivum throughout the water column at Stns. 35-11 and 35-13. The absence of this species in response to the difference in the low-salinity surface water mass at Stn. 35-15 during winter indicated the invasion of shallow water mass from China. The sensitivity of this species to such hydrological changes provides a valuable insight into the vertical migration of the YSBCW.
PubDate: 2023-01-13
- Influence of Nutrient Gradient on Phytoplankton Size Structure, Primary
Production and Carbon Transfer Pathway in a Highly Productive Area (SE
Mediterranean)-
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Abstract: Abstract We assessed the spatial variability in the size structure of phytoplankton, community composition, primary production and carbon fluxes through the planktonic food web of the Gulf of Gabès (GG; Southeastern Mediterranean Sea) in the fall of 2017 during the MERMEX-MERITE cruise. High concentrations in nutrients, chlorophyll a (~ 2–6 µg L−1) and primary production (1816–3674 mg C m−2 d−1) revealed an eutrophic status of the studied stations in the GG. In accordance with hydrodynamic features, inorganic nutrients showed increases in concentrations from North to South and from coast to offshore, these nutrient gradients impacting the spatial distribution of phytoplankton community. Size-fractioned phytoplankton biomass and production were the lowest in the northernmost zone where they were mainly sustained by pico-sized fraction. Concomitantly, in this area, small aloricate ciliates were dominant leading to a high microbivory. Conversely, higher biomass and production were measured towards the South and offshore with prevalence of larger phytoplankton (nano- and/or micro-sized fractions) supported by diatoms. The herbivorous protozooplankton and metazooplankton were more abundant in these zones, resulting in an increase of the herbivory. The vertical particulate organic carbon flux followed also a north–south and coast-offshore increasing gradient, with a higher contribution of phytoplankton, and zooplankton fecal pellets to the sinking organic matter in the southernmost area. Our results suggest that even in nutrient-rich and highly productive waters, a continuum of trophic pathways, ranging from microbial to multivorous and herbivorous food webs, may exist, which implies different efficiencies in carbon export and carrying capacity within the ecosystem.
PubDate: 2023-01-13
- Sea Urchin Removal and Effectiveness Evaluation from the Long-Term
Monitoring Data in Dokdo, Korea-
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Abstract: Abstract Dokdo is located 215 km away from the Korean Peninsula and is not affected by anthropogenic impacts. In this area, barren grounds developed between the late 1990s and early 2000s. The Korean government has measured the average urchin density from 1 to 10 sampling stations around Dokdo during 2006–2020 and has been conducting urchin removal projects annually since 2015 all around the bottom of Dokdo within depths of 5–20 m. Here, we implemented an additive decomposition method for time series analysis of the collected data. The timeline was divided into two periods: sample data period for predicting the urchin density (2006–2016) and intervention period (2016–2020). A trend model was estimated from the de-seasonalized data of the prediction period. Subsequently, forecasts were compared with the corresponding observations of the intervention period. While the forecasts reflected the spread of barren grounds and sea urchins, the actual urchin density during the intervention period decreased. On comparing the macroalgal coverage between the springs of 2017 and 2020, the samples with coverage less than 20% decreased from 50% in 2017 to 0% in 2020, while those with 21–40% coverage increased from 30% in 2017 to 90% in 2020. These changes confirmed the effect of urchin removal, and, based on this and other studies, an effective threshold of urchin density/biomass of two individuals and 140–150 g/m2 was suggested as the target criterion. The study proved the urchin removal as an effective solution to recover macroalgal beds in Dokdo.
PubDate: 2023-01-04
DOI: 10.1007/s12601-022-00094-8
- Effects of Hydrodynamic Disturbance on Vegetation Development in Coastal
Salt Marshes: A Model Study in Jiangsu, China-
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Abstract: Abstract Salt marshes are now known to improve coastal safety by attenuating waves and stabilizing the bed. Meanwhile, for salt marsh conservatin and restoration, a great deal of research has been done on the establishment mechanism of vegetation in salt marshes. However, research on the effects of hydrodynamic disturbance on the development of salt marsh vegetation is limited. The purpose of this paper is to investigate how the hydro-morphodynamic process affects the establishment and expansion of plants in salt marshes and to simulate the establishment process. First, we used a 2D finite-element model to simulate hydro-morphodynamics in the selected tidal flat in Jiangsu, China. We then defined the variables describing the frequency and magnitude of hydrodynamic disturbance and quantified the effects of disturbance on plant establishment using Spearman correlation coefficients. Finally, the vegetation development process was further analyzed using a logistic regression model, and the vegetation development in the study area was simulated from 2017 to 2021. The results show that salt marsh vegetation colonization has a relatively high correlation with flooding time and bed shear stress (ρ > 0.6), and bed shear stress is the main hydrodynamic disturbance parameter limiting further expansion of salt marsh vegetation. The method combining hydrodynamic modeling and logistic regression has the potential to be used to identify hydrodynamic disturbances in future salt marsh restoration and management processes and to help design appropriate restoration measures.
PubDate: 2023-01-04
DOI: 10.1007/s12601-022-00097-5
- Estimating Bed Shear Stress Distribution over Bottom of a Channel on the
Moving Vessel-
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Abstract: Abstract Shear stress is critical in the determination and estimation of bedload transport and morphological changes. Generally, the bed shear stress is estimated in fields using three-dimensional flow velocities acquired by an acoustic Doppler velocimeter and current profiler mounted on the channel bottom or anchored vessel. The temporal measurement and estimation of the bed shear stress by the conventional methods in a fixed point must be significantly close to the actual bed shear stress; however, the conventional methods may not provide sufficient information of spatial distribution of the bed shear stress over the entire domain, i.e., the measurements in several fixed points cannot guarantee that the measured values represent the entire domain of interest. Therefore, the present work proposed a framework for acquiring the spatial distributions of shear stress over a domain. Accordingly, a reach with a length and width of 5.6 km and 250 m, respectively, at the end of the Hyeongsan River in South Korea was surveyed through the moving-vessel measurement with ADCP measuring the velocities of that channel reach to estimate shear stress. To collect over a possible maximum spatial domain in a short duration, the moving-vessel technique was applied over the survey region without stopping a vessel. The measurement was conducted in a series of single zigzag transects instead of repeatedly transects over a same cross section. The spiked noises of velocity were observed in high frequencies at a single transect and so the noises were smoothed by moving average over a reasonable circular space. After the spatial interpolation, the accuracy of the spatial distributions of the bed shear stress was compared to the anchored-vessel measurement, and the reliable bed shear stress map was provided as a result.
PubDate: 2023-01-04
DOI: 10.1007/s12601-022-00095-7
- Chemical Speciation of Dissolved Copper in the Nakdong River Estuary and
Its Relationship with Humic-Like Fluorescent Dissolved Organic Matter-
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Abstract: Abstract The total dissolved copper (Cu) concentrations, chemical speciation, and intensities of humic-like fluorescent dissolved organic matter (FDOMH) components were determined in the Nakdong River Estuary. The concentrations of total dissolved Cu ranged from 4.6 to 13.3 nM and showed an inverse correlation with salinity (R2 = 0.93), indicating a conservative mixing trend in the Nakdong River Estuary. The chemical speciation of dissolved Cu was determined by competitive ligand equilibrium adsorptive cathodic stripping voltammetry, and speciation parameters were calculated using ProMCC software. The concentrations of the strong Cu-binding organic ligands (L1) ranged from 3.1 to 96 nM, whereas those of the weak ligand (L2) ranged from 10 to 3400 nM. Both L1 and L2 concentrations were relatively high at the upper sampling sites (river water sites) and decreased in proximity to the coastal sea, indicating that Cu-binding organic ligands from terrestrial sources may be dominant in the Nakdong River Estuary. Although Cu-binding organic ligands showed positive correlations with FDOMH, anomalously high concentrations of Cu-binding organic ligands were observed at river water sites, suggesting additional sources of organic ligands. Our results suggest that Cu-binding organic ligands originated from various sources in estuarine environments.
PubDate: 2023-01-04
DOI: 10.1007/s12601-022-00098-4
- Sea Surface Temperature and Phytoplankton Abundance as Crucial Proxies for
Green Noctiluca Bloom Monitoring in the Northeastern Arabian Sea: A Case
Study-
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Abstract: Abstract Green Noctiluca scintillans (NSG) is a mixotrophic dinoflagellate that frequently forms intense blooms in the north Indian Ocean, especially in the northeastern Arabian Sea during winter. This study investigates the conducive conditions and drivers associated with NSG blooms and proposes significant models for estimating NSG based on in situ (time-series) study during the bloom cycles. Two critical factors with regard to the blooms, i.e., phytoplankton abundance and sea surface temperature (SST), were examined. The first phase of heterotrophy dominance was when moderate blooms up to ~ 2.26 × 104 cells 1–1 occurred and, when NSG cells per unit chlorophyll-a (chl-a) increased, SST decreased up to ~ 24.5 ºC. The bloom intensity was proportional to the feed (diatoms/phytoplankton) availability and the degree of cooling (by the winter convection, i.e., nutrient enrichment). In the second phase of autotrophy dominance, intense blooms up to 1.9 × 105 cells l−1 occurred and NSG cells per unit chl-a fell, when the SST increased. During this period, bloom intensity was proportional to the degree of warming, i.e., nutrient and physiological stress. Phytoplankton are related to NSG by a single linear model through this SST cycle and is likely the NSG’s essential biotic precursor. Attention is then focused on developing a remote sensing reflectance (Rrs) model for efficient synoptic monitoring of NSG using ocean color satellites. The Rrs band product ratio, a new metric, in combination with SST, notably modelled NSG abundance, which may be of potential routine application.
PubDate: 2023-01-04
DOI: 10.1007/s12601-022-00096-6
- Gulf of Urabá (Caribbean Colombia), a Tropical Estuary: A Review with
Some General Lessons About How it Works-
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Abstract: Abstract Estuaries are highly diverse ecosystems that occur at the interface between land and sea and thus possess a high degree of environmental variation over short spatial and temporal scales. The Gulf of Urabá (1800 km 2; mean depth ~ 40 m) is a semiclosed estuarine area located in the southwestern part of the Caribbean Sea (South America). This large coastal–estuarine ecosystem operates as a biogeochemical reactor due to it featuring examples of high nutrient concentrations on the surface (NO 3- = 1619 μM; NO 2- = 0.505 μM; NH 4+ = 2.938 μM; PO 4 3- = 7.603 μM), high Chl α (max = 30.17; min = 0.02; mean = 9 mg m−3), as well as blooms of toxic algae, mostly Pseudo-nitzschia pseudodelicatissima. An outbreak of Tripos fusus causes bioluminescence and about 20 events of hypoxia (< 2–4 mg O 2 L−1) within a time series of 10 years. Despite this, information regarding the biological and biogeochemical oceanography (chlorophyll α, biomass, planktonic composition, nutrient cycling, mass balance of elements, and interannual variability) remains non-existent. Therefore, elucidating an ecosystem’s thresholds for various features is necessary for managing marine ecosystems, and especially for climate change projections. We here present a review of the functioning of this estuary, evaluating and reviewing each aspect of oceanographic variability.
PubDate: 2022-12-02
DOI: 10.1007/s12601-022-00093-9
- Comparing Environmental DNA Metabarcoding and Underwater Visual Census to
Monitor Korean Coastal Fish Community-
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Abstract: Abstract This study conducted underwater visual census (UVC) and eDNA metabarcoding to survey fish fauna in the coastal waters off Busan (Cheongsapo) and Ulsan (Bangeojin), Southeast sea of Korea, after which the two survey methods were compared. A total of 49 species were identified in Cheongsapo (eDNA metabarcoding: 29 species; UVC: 29 species) and 60 were identified in Bangeojin (eDNA metabarcoding: 43 species; UVC: 30 species), which accounted for 70 species in both areas. Except for 13 species without GenBank sequence data, 80% of the species detected using UVC were detected through eDNA metabarcoding. In addition, eDNA metabarcoding enabled the detection of 33 species that were otherwise not detected by UVC. Thus, eDNA can be used to conduct fast and wide fish diversity surveys and is applicable to microhabitats in coastal areas. Therefore, eDNA could become an important complement to traditional surveys for monitoring marine biodiversity.
PubDate: 2022-12-01
DOI: 10.1007/s12601-022-00082-y
- Meiofauna and Nematode Community Composition in Maxwell Bay, King George
Island, Antarctica-
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Abstract: Abstract The Antarctic Ocean hosts several species adapted to polar environments. However, the Antarctic marine environment is rapidly changing. We studied the meiofauna and nematode communities in Maxwell Bay, King George Island, Antarctica. The meiofaunal densities ranged from 174.3 ± 6.2 to 377.9 ± 7.0 individuals/10 cm2. The nematodes and harpacticoids accounted for 89.7% of the total meiofaunal density. A total of 1448 nematode individuals across 34 genera were recorded. The dominant nematode genus was Molgolaimus. This study offers guidance for future studies on polar benthic organisms and a reference to evaluate anthropogenic effects on polar ecosystems.
PubDate: 2022-11-09
DOI: 10.1007/s12601-022-00092-w
- Numerical Study of Influencing Factors on Tidal Wave Propagation in the
Persian Gulf-
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Abstract: Abstract A 2D hydrodynamic model is employed to study the characteristics of tidal wave propagation in the Persian Gulf (PG). The study indicates that tidal waves propagate from the Arabian Sea and the Gulf of Oman into the PG through the Strait of Hormuz. The numerical model is first validated using the measured water levels and current speeds around the PG and the principal tidal constituents of Admiralty tide tables. Considering the intermediate width of the PG, in comparison to the Rossby deformation radius, the tidal wave propagates like a Kelvin wave on the boundaries. Whereas the continental shelf oscillation resonance of the basin is close to the period of diurnal constituents, the results show that the tide is mixed mainly semidiurnal. A series of numerical tests is also developed to study the various effects of geometry and bathymetry of the PG, Coriolis force, and bed friction on tidal wave deformation. Numerical tests reveal that the Coriolis force, combined with the geometry of the gulf, results in the generation of different amphidromic systems of diurnal and semidiurnal constituents. The configuration of the bathymetry of the PG, with a shallow zone at the closed end of the basin that extends along its longitudinal axis in the southern half (asymmetrical cross section), results in the deformations of incoming and returning tidal Kelvin waves and consequently the shifts of amphidromic points (APs). The bed friction also results in the movements of the APs from the centerline to the south border of the gulf.
PubDate: 2022-11-07
DOI: 10.1007/s12601-022-00091-x
- Sub- and Marine Mediterranean Basin Antimicrobial Resistance and
Environmental Concerns: A Case Study of Tunisia-
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Abstract: Abstract Antibiotics are a growing contaminant of substantial concern, principally in the aquatic environment, because of their pseudo-persistence and biological activity, and they have received a lot of attention in the recent decade. The spread of antibiotic-resistant bacteria and their antibiotic-resistant genes have showed expansion in most natural surroundings, including water, soil, and sediments, causing and presenting health problems for humans and animals. The ecological impact and environmental concerns of antibioresistance in aquatic and littoral habitats are highlighted in this review. Antibiotic pollution levels in marine, coastal water lakes, and river water flowing into the Mediterranean Sea were reported in all gathered data. Likewise, this paper showed that there was a significant lack of data and information about this pollution in seawater and general aquatic environments, revealing a substantial difficulty in following and studying these new qualities of pollutants and their main fates in natural environments. Also, their impact on the marine and lake environment in terms of the emergence of drug-resistant bacteria and drug-resistant genes was described.
PubDate: 2022-10-25
DOI: 10.1007/s12601-022-00090-y
- Erratum to: Spatio-Temporal Variation of the M2 Tidal Current from Field
Observations in the Jeju Strait-
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PubDate: 2022-09-13
DOI: 10.1007/s12601-022-00088-6
- Reproductive and Growth Parameters of the Razor Clam, Cultellus maximus
(Gmelin, 1791), in Southern Vietnam-
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Abstract: Abstract This study aimed to analyze the sex ratio, spawning seasons, length at first maturity, length distribution, length–weight relationship, and relative condition factor of Cultellus maximus (Gmelin, 1791) in Southern Vietnam. A total of 1037 individuals of C. maximus were collected at 3 sampling sites from June, 2019 to June, 2020. The sex ratio was found to be female biased in Can Gio and male biased in Phu Tan and Ngoc Hien. The clam spawns throughout the year, peaking at Q2 and Q3 during the rainy season. Pooled length at first maturity was 10.12 cm (9.65–10.49 cm CI 95%, P-value < 2.2·10–16). The length–weight relationship indicates positive allometric growth. This study suggests that imposing a minimum harvest size limit on C. maximus using the length at first maturity as reference and with harvest seasons in Q1 in Ngoc Hien and Can Gio and Q2 or Q3 in Phu Tan would be ideal for consumption of this species.
PubDate: 2022-09-02
DOI: 10.1007/s12601-022-00089-5
- Estimation of Potential Habitats for Three Species of Bivalves Using the
Habitat Variables in Gomso Bay Tidal Flat, Korea-
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Abstract: Abstract The gradual changes in the habitat of Gomso Bay negative impacted the intertidal flat aquaculture of the Manila clam Ruditapes philippinarum. The habitat evaluation of the Manila clam in Gomso Bay tidal flat that should be preceded to identify this negative impact in clam culture was conducted using the habitat variables chlorophyll-a, hydrodynamics, sediment sand, exposure time, dissolved oxygen, and salinity. Additionally, to utilize the unsuitable sites of Manila clam culture, we used the habitat suitability index by subdividing substrate variables (sorting coefficient, silt content, and mean grain size) for two species (Cyclina sinensis and Mactra veneriformis). As a result, the lower flat was chosen as the optimal habitat for Manila clam, with a habitat suitability index mean score of 0.62 and the upper flat was deemed to be the potential habitat for C. sinensis, while the middle flat was chosen for M. veneriformis. Therefore, the possibility of using unsuitable sites for Manila clam farming as alternative species was identified. These findings can be used as a reference for optimal site selection for the diversification of commercial species and decentralization of clam culture farms in the Gomso Bay tidal flat.
PubDate: 2022-08-04
DOI: 10.1007/s12601-022-00085-9
- Spatio-Temporal Variation of the M2 Tidal Current from Field Observations
in the Jeju Strait-
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Abstract: Abstract The variability in the tidal current in the Jeju Strait was investigated based on sea surface current fields observed by a high-frequency (HF) radar and vertical current profiles observed by three bottom-moored acoustic Doppler current profilers (ADCPs). The monthly M2 tidal current, the most dominant constituent in the study area, had significant temporal variability, and there were spatial changes in the temporal variation trend. While the semi-major axis of the M2 tidal current in winter was stronger than that in summer in some parts of the HF radar observation range, the summertime semi-major axis was stronger than that in wintertime in other parts of the observation range. Both opposite trend areas coexisted within the HF radar coverage area of several tens of kilometers. The vertical structure of the tidal currents in winter was similar to the theoretical structure in which Ekman dynamics was applied under depth-independent vertical eddy viscosity, and the year-to-year change was weak. In contrast, the vertical structure of the tidal currents in summer significantly varies over depth and years. Furthermore, the seasonal variation patterns at the three ADCP stations differed spatially. The temporal and spatial variability of tidal currents could be explained as a result of the strengthening stratification and, consequently, semidiurnal internal tides in summer. In summer, an internal tide with a wavelength of tens of kilometers could be generated in the vicinity of and propagate into the study area. The overlapping and offsetting of the barotropic and internal tidal components within the HF radar observation range caused complex spatial variations.
PubDate: 2022-08-01
DOI: 10.1007/s12601-022-00084-w
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