Mouth Of Bay Research Articles

Perturbation of Boundary Conditions to Create Appropriate Ensembles for Regional Data Assimilation in Coastal Estuary Modeling

AbstractRegional data assimilation is conducted for a coastal estuary using the ensemble Kalman filter, real observation data from Ise Bay, Japan, and a simulation model called the Ise Bay Simulator. The applicability and robustness of the method are then examined. We also analyze the relationship between the boundary conditions, which add perturbations and the data assimilation results of water temperature and salinity. A method of creating an ensemble by perturbing three boundary conditions (atmospheric forcing, lateral boundary conditions [open boundary conditions], and river discharge forcing) is then proposed. In situ water temperature and salinity profiles observed at fixed points are assimilated daily. The proposed assimilation method provides stable data assimilation without unnatural values for water temperature and salinity throughout the year. Further, applying a perturbation to the three boundary conditions does not lead to filter divergence, thus indicating good applicability and robustness, that is, applying a perturbation to the three boundary conditions does not degenerate the ensemble spread. According to a sensitivity experiment, perturbing the atmospheric boundary conditions of both air temperature and wind speed increases the ensemble spread of water temperature, especially near the surface layer. Wind speed has the greatest influence on the magnitude of the salinity ensemble spread, and its dominance depends on location. Perturbation of lateral boundary conditions increases the ensemble spread of water temperature and salinity at all water depths near the bay mouth, and the observations are effectively assimilated. Perturbation of river discharge forcing successfully assimilates water temperature and salinity near the estuary.

Normal incidence reflection coefficient measurements of layered sand-mud sediment and comparison to models

Depth-dependent variability in seabed acoustic and geophysical properties can be introduced by both physical and biogenic processes. An experiment was conducted near the mouth of Mobile Bay, Alabama to investigate spatial variability over a mud-sand gradient, where sediment properties showed lateral changes on the scales of tens of meters. Additionally, sediment layering on the scale of centimeters was evident in the top 20 cm of the seabed. Normal-incidence seabed reflection coefficient measurements (20–60 kHz) were acquired using a ship-mounted system to survey a 1.9 km2 area of the seabed, and diver cores were collected for direct analysis of near-surface seabed properties. The cores were acoustically logged to obtain vertical profiles of sound speed and attenuation (10–1000 kHz) and then analyzed for vertical profiles of sediment physical properties (porosity, grain size, organic matter content), infauna community composition, and tensile strength. Physical and acoustic profiles obtained from the cores were then used as inputs to model the n-layer reflection coefficient. Comparison of the modeled and measured reflection coefficients will be discussed. [Work supported by ONR.]

Acoustic spectrometry of bubbles in an estuarine front: Sound speed dispersion, void fraction, and bubble density.

Estuaries constitute a unique waveguide for acoustic propagation. The spatiotemporally varying three-dimensional front between the seawater and the outflowing freshwater during both flood and ebb constitutes an interfacial sound speed gradient capable of supporting significant vertical and horizontal acoustic refraction. The collision of these two water masses often produces breaking waves, injecting air bubbles into the water column; the negative vertical velocities of the denser saltwater often subduct bubbles to the bottom of these shallow waveguides, filling the water column with a bubbly mixture possessing a significantly lower effective sound speed. A field experiment was carried out in the mouth of Mobile Bay, Alabama in June 2021 to characterize estuarine bubble clouds in terms of their depth-dependent plume structure, frequency-dependent sound speed and attenuation, bubble size distribution, bubble number density, and void fraction. Results demonstrate that sound speed in the bubbly liquid consistently falls below the intrinsic sound speed of bubble-free water; specifically, the bubbly liquid 1.3 m below the surface in a front in this environment possesses effective sound speeds, void fractions, and bubble number densities of approximately 750 m/s, 0.001%, and 2 × 106 bubbles/m3, respectively.

Alternative migratory strategies related to life history differences in the Walleye (Sander vitreus)

BackgroundWhile Pace of Life Syndrome predicts behavioural differences between individuals with differential growth and survival, testing these predictions in nature is challenging due to difficulties with measuring individual behaviour in the field. However, recent advances in acoustic telemetry technology have facilitated measurements of individual behaviour at scales not previously possible in aquatic ecosystems.MethodsUsing a Walleye (Sander vitreus) population inhabiting Black Bay, Lake Superior, we examine whether life history characteristics differ between more and less mobile individuals as predicted by Pace of Life Syndrome. We tracked the movement of 192 individuals from 2016 to 2019 using an acoustic telemetry study, relating patterns in annual migratory behaviour to individual growth, and seasonal changes in optimal thermal-optical habitat.ResultsWe observed two consistent movement patterns in our study population—migratory individuals left Black Bay during late summer to early fall before returning to the bay, whereas residents remained within the bay year-round. The average maximum length of migrant Walleye was 5.5 cm longer than residents, and the sex ratios of Walleye caught during fall surveys was increasingly female-biased towards the mouth of Black Bay, suggesting that a majority of migrants were females. Further, Walleye occupancy outside of Black Bay was positively associated with increasing thermal-optical habitat.ConclusionsWalleye in Black Bay appear to conform to Pace of Life Syndrome, with migrant individuals gaining increased fitness through increased maximum size, which, given size-dependent fecundity in this species, likely results in greater reproductive success (via greater egg deposition vs. non-migrants). Further, apparent environmental (thermal) controls on migration suggest that migratory Walleye (more so than residents) may be more sensitive to changing environmental conditions (e.g., warming climate) than residents.

South Brazil pre-colonial sharks: Insights into biodiversity and species distributions.

South Brazil's archaeological coastal sites (shellmounds and middens) show a diverse collection of shark faunal remains, some of which belong to species considered rare nowadays for the region. However, shark archaeological remains identification in this region has been historically insufficient and prone to mistakes. This study identified shark fauna and estimated body size (total length) present at two archaeological sites: Rio do Meio (1220-977 Cal B.P.) and Enseada II (4286-3783 Cal B.P.), located in Santa Catarina, South of Brazil. Here, 1600 teeth and 3588 vertebrae were analysed and identified. We showed higher historical shark species richness than previously reported for South Brazil in historical and archaeological studies. In total, we identified at least 15 species of sharks (11 species and four identifications at the genus level). The presence of juvenile shark remains adds to the evidence of pre-colonial fishing impacts in local shark populations. The consistent recovery of adults and juveniles of Carcharias taurus points to a possible nursery area on the mouth of Babitonga bay. The high teeth frequency (43%) of C. taurus suggests the South Brazil coastline was once home to abundant populations of this critically endangered species. Furthermore, we discuss the presence of rare species nowadays, suggesting a possible historical residency for adult populations of Carcharodon carcharias based on the presence of juveniles and young-of-the-year on archaeological sites. The occurrence of Negaprion brevirostris, a tropical species, might have been facilitated by ocean current variations.

Linking ecosystem services to a coastal bay ecosystem health assessment: A comparative case study between Jiaozhou Bay and Daya Bay, China

Coastal bays, situated within Earth’s critical zone, play important ecological and socioeconomic roles. This study developed an integrated ecosystem health assessment framework based on ecosystem services specific to coastal bays, particularly exploring approaches to determine critical indicators and establish a reference benchmark. The framework was applied to two typical coastal bays (Jiaozhou Bay and Daya Bay) to ascertain significant health differences, subsequent challenges and prospective management. Comparatively, Daya Bay was healthier. Daya Bay received an overall comprehensive index ecosystem health score of 69.42 (good); however, its ecosystem services scores differed significantly (supporting services = 71.34, regulating services = 87.29, provisioning services = 3.59, cultural services = 74.30), indicating severe degradation in its ecosystem food provisioning function. Jiaozhou Bay received corresponding score of 55.79 (moderate), and its ecosystem services scores were relatively lower (supporting services = 63.31, regulating service = 54.30, provisioning services = 6.18, and cultural services = 54.74), indicating widespread ecosystem degradation. The health status of coastal bays is closely associated with both natural characteristics and human interventions. The narrow bay mouth of Jiaozhou Bay, its limited enclosed seawater area, and the intensive land reclamation that has taken place since the 1950s have directly or indirectly led to the low score of most of its indicators, particularly regarding the significant reductions in its water area and shoreline. The geological advantages of Daya Bay is its large area of water and that it is open to the outer sea, which have contributed to its comparatively healthier status, wherein scores of only a few indicators were bad (i.e., biological indicators of sensitive organisms in the upper food chain). Results from this study provide important information for prospective bay management. For Jiaozhou Bay, more effort should be paid to improving ecosystem health in a comprehensive way, particularly fishing control, land reclamation control and habitat restoration. For Daya Bay, overfishing should be better controlled, while more emphasis should be paid to protecting and restoring certain moderately specific habitats and species. For effective management, we highlight that ecosystem management strategies needs to be differentiated among different bays based on their significant natural and social features. Our approach provides a practical ecosystem health assessment tool that can be applied to other coastal bays to better inform sustainable management and conservation initiatives.

Satellite Remote Sensing of Water Quality Variation in a Semi-Enclosed Bay (Yueqing Bay) under Strong Anthropogenic Impact

The semi-enclosed bays impacted by heavy anthropogenic activities have weak water exchange and purification capacities. Most of the sea bays have suffered severe eutrophication, water quality deterioration, ecosystem degradation and other problems. Although many countries and local governments have carried out corresponding environmental protection actions, the evaluation of their effectiveness still requires monitoring technology and data support for long-term water environment change. In this study, we take Yueqing Bay, the fourth largest bay in China, as a case to study the satellite-based water quality monitoring and variation analysis. We established a nutrient retrieval model for Yueqing Bay to produce a long-term series of nutrient concentration products in Yueqing Bay from 2013 to 2020, based on Landsat remote sensing images and long-term observation data, combined with support vector machine learning and water temperature and satellite spectra as input parameters, and then we analyzed its spatiotemporal variations and driving factors. In general, nutrient concentrations in the western part of the bay were higher than those in the eastern part. Levels of dissolved inorganic nitrogen (DIN) were lower in summer than in spring and winter, and reactive phosphate (PO4-P) levels were lower in summer and higher in autumn. In terms of natural factors, physical effects (e.g., seasonal variations in flow field) and biological effects (e.g., seasonal differences in the intensity of plankton photosynthesis) were the main causes of seasonal differences in nutrient concentration in Yueqing Bay. Nutrient concentration generally increased from 2013 to 2015 but decreased slightly after 2015. Over the past decade, the economy and industry of Yueqing Bay basin have developed rapidly. Wastewater resulting from anthropogenic production and consumption was transported via streams into Yueqing Bay, leading to the continuous increase in nutrient concentrations (the variation rates: aDIN>0, aPO4−P>0), which directly or indirectly caused high nutrient concentrations in some areas of the bay (e.g., Southwest Shoal at the mouth of Yueqing Bay). After 2015, the various ecological remediation policies adopted by cities around Yueqing Bay have mitigated, to some extent, the increasing nutrient concentration trends (the variation rates: aDIN<0, aPO4−P<0), but not significantly (P > 0.1). The environmental restoration of Yueqing Bay also requires continuous and long-term ecological protection and restoration work to be effective. This research can provide a reference for ecological environment monitoring and remote sensing data application for similar semi-enclosed bays, and support the sustainable development of the bay.

Analysis of oligotrophic factors in seaweed farms using ecosystem models —Cases in the Matoya Bay area at the mouth of Ise Bay—

Analysis of oligotrophic factors in seaweed farms using ecosystem models —Cases in the Matoya Bay area at the mouth of Ise Bay—

Spatial patterns in wave signatures on beaches in estuaries and bays

Sandy beaches in estuaries and bays (BEBs) are ubiquitous around the world. While some are referred to as “low energy” beaches, there are large differences in wave climate due to fetch, swell exposure and shoreface morphology. In this study, wave-climate controls on BEB morphology are identified relative to bay geometry and focusing on the relative contributions of wind, ocean swell and infragravity waves to the wave signature of a BEB. We focus on two swash-aligned and two drift-aligned BEBs in an urbanized, semi-enclosed bay in SE Australia (Kamay/Botany Bay), with differences in proximity to the bay mouth, beach aspects and fetch, as well as different histories of storm erosion and recovery. Spectral analysis of local wave measurements (June 2018–January 2019) shows that wave signatures at all 4 BEBs are dominated by swell waves (>51%), followed by locally generated wind waves at 3 out of 4 BEBs (<43%), then infragravity waves (<35%). We identified five weather scenarios based on local wind speed/direction and resultant wind waves, combined with infragravity waves, and offshore swell wave conditions. BEBs close to the bay entrance are primarily controlled by swell waves, but at times even BEBs close to the entrance can be sheltered from swell waves depending on their incident angle. Conversely, BEBs farthest from the bay entrance (~8 km) alternated between periods where spectra were dominated by either wind waves or offshore swells. Infragravity waves were only important relative to wind waves and swell at the most sheltered BEBs, where there is limited fetch and swell dissipated over shallow areas. We also show that anthropogenic factors such as constructed revetments or groynes significantly alter wave signatures at BEBs in this bay. Thus, wave spectral signatures are highly variable across BEBs in the same bay and can represent a simple tool to study BEB morphodynamics including storm response and subsequent recovery.

Anthropogenic plutonium radioisotopes in the ecosystem components of Sevastopol Bay (the Black Sea)

Modern levels (2010-2020) of 239+240Pu activity concentration in Sevastopol Bay (Black Sea) surface waters, 0-5 cm layer of bottom sediments and hydrobionts were determined by multistage radiochemical technique. The 239+240Pu activity concentrations in Sevastopol Bay surface water were on relatively low level: 1.08±0.09 - 1.54±0.17 mBqnr3. The maximum value of 239+240Pu activity concentration in the bottom sediments surface layer was observed in Sevastopol Bay mouth (993±90 mBqkg1) and it decreased with distance from the bay entrance to its tail end down to the minimum value - 276±53 mBqkg1. Based on these results as well as on published data the 239+240Pu deposition density distribution in the bay boxes and their inventory in 0-5 cm layer of bottom sediments were estimated in every boxes. Total 239+240Pu inventory in the bottom sediments surface layer was estimated at 121 MBq, with the highest deposition density value determined in the mouth part of the bay. Among studied hydrobiont species the highest 239+240Pu content was determined for mollusks (for their shells) Mytilus galloprovincialis (Lamarck, 1819) while the lowest - for fish Scorpaena poreus (Linnaeus, 1758). Accumulation ability of studied ecosystem components of Sevastopol Bay against 239+240Pu was characterized by evaluating concentration factors (Cf). It was shown that the bottom sediments of the bay were the main depot for plutonium anthropogenic radionucludes (Cf (239+240Pu) = n-105). The Cf (239+240Pu) were from two to three orders of magnitude lower for the hydrobionts of the bay: n-103 for brown algae and mollusks and n-102 for green algae and fish.

Redox conditions of bottom sediments and macrozoobenthos characteristics in the Kruglaya and Kazachya bays (Sevastopol)

A lack of systemic and environmentally efficient approach to exploitation of the Kruglaya and Kazachya bays (Sevastopol) resulted in their severe pollution. The conjunction of natural and anthropogenic factors led to deterioration of habitat conditions of benthic communities. The aim of this work was to carry out complex research of Kruglaya and Kazachya bays’ ecosystems to study peculiarities of formation of redox conditions in bottom sediments and bottom water layer, as well as their effect on macrozoobenthos characteristics. Bottom sediments were sampled by diver in plexiglass tubes hermetically sealed at the top and bottom; it helped in preserving a fine structure of bottom sediments and bottom water layer. To study benthic communities, samples were taken in the same spot with a manual sampler. To obtain chemical composition of pore waters with high vertical resolution, the voltammetry analysis was carried out. Calculation of an oxygen flux at the boundary and in the upper layer of bottom sediments was performed according to the vertical profile of oxygen concentration in pore waters and geochemical analysis with applying the equation for the Fick’s first law and considering concentration gradient and molecular diffusion of oxygen in pore waters. Standard hydrobiological methods were applied for the analysis of benthic material. When calculating the values of the Shannon diversity index (H’), the binary logarithm was used. The data analysis showed as follows: a high level of anthropogenic load and restricted water dynamics resulted in siltation of bottom sediments in the studied water areas, which obstructed oxygen penetration; the accumulation of organic carbon contributed to its active consumption. Stratification of a water column due to limited water exchange, high temperature of bottom water, accompanied by a decrease in oxygen solubility, and finely dispersed nature of bottom sediments contributed to the fact that the rate of oxygen input was lower than the rate of oxygen consumption for organic matter oxidation. This was followed by the development of oxygen deficiency zones and emergence of reduced compounds, in particular hydrogen sulfide. Importantly, suboxic conditions prevailed in the upper sediment layer, and anaerobic conditions prevailed below. Due to this, the main forms of macrozoobenthos were species tolerant to oxygen deficiency and organic pollution. Specifically, in some spots of the Kazachya Bay, polychaetes alone were recorded. At the same time, in the Kruglaya Bay mouth area, intense water dynamics and morphological peculiarities of bottom sediments contribute to saturation of the upper sediment layer with oxygen. Based on oxygen concentration data for the surface (0–5 mm) sediment layer (pore waters) and on geochemical peculiarities of bottom sediments (moisture and porosity), the oxygen flux at st. 4 (the Solenaya Bay) was calculated; the value was 0.73 M·m−2·year−1. Considering oxygen concentration in bottom water layer (259 μM), the time for complete depletion of oxygen or its renewal is about 5 months if taking into account biogeochemical processes alone. Hence, it can be assumed that the ecosystems of the Kruglaya and Kazachya bays are in the stage of degradation. Their further exploitation without a developed systemic and rational approach will result in a critical deterioration of the ecosystems – the emergence and spread of environmental risk zones. It will reduce the recreational and socioeconomic attractiveness of these areas.

Characterization of hydrological features and plankton during neap tides in a subtropical lagoon south of the California Current

ABSTRACT This study aimed to characterize their Spatio-temporal distribution of hydrological variables and plankton during neap tides in Bahía Magdalena, a subtropical lagoon south of the California Current. We compare data from surface and bottom waters of stations located inside the lagoon with those near the bay's mouth and between surface and bottom. The availability of nutrients and the chlorophyll-a are associated primarily with the intense upwelling activity in spring. Due to direct marine influence, this relationship was more significant at the inlet than inside the lagoon, especially at the bottom. During the intense upwellings marine influence is maintained even during neap tides. The wind probably causes the homogeneous distribution in most variables within the bay's surface; this may also contribute to the re-suspension of nutrients due to vertical water column mixing. Abiotic variables were not linearly related with zooplankton biovolume and the density of diatoms and dinoflagellates. Phytoplankton was composed mainly by the micro fraction and diatoms during spring and nanoplankton in the warmest season of the year; however, the strong upwellings at the spring's end caused a HAB composed for diatoms. Chlorophyll-a concentration and diatoms were more abundant inside the lagoon and could explain the lower nutrient concentration of that zone. Zooplankton biovolume seasonality differed from other years, with higher values during winter and a significant decreasing trend throughout the year, resulting from the phytoplankton variability. Upwelling and wind variability explains the high biological productivity observed over most of the year.

Variation of water mass exchange on tidal scale in Balikpapan Bay

Balikpapan Bay is enclosed water influenced by freshwater from river runoff and saline water from Makassar Strait. The exchange of water mass was examined by 3D numerical model simulation-Hamburg Shelf Ocean Model (HAMSOM) with horizontal resolutions approx. 150 m and 10 vertical layers applied in Balikpapan Bay. The thirteen tidal components, daily river runoff, atmospheric forcing, subsurface temperature, and Salinity in 3D used for model input. The tidal elevation from Geospatial Information Agency (BIG) model fits with this result from 01/03/2020 to 31/03/2020. It has coefficient correlation 0,99 with a significant level of 95% and Root Mean Square Error (RMSE) is 0,1 m. The volume and salt transport in the mouth (Line-A) and middle (Line-B) of bay was examined. The maximum transport in Line-A during spring (neap) high to low tide and low to high tide is −18364.72 m3/s (−1717.57 m3/s) and −17532.27 m3/s (4258.86 m3/s) for volume. Then, 531,947,898.90 kg.psu./s (−45,127,135.38 kg.psu./s) and −536,410,944.50 kg.psu./s (140,700,437.97 kg.psu./s) for salinity. Positive (negative) of water transport is inflow (outflow) to Balikpapan Bay. The net transport in a day during the spring (neap) is −832.45 m3/s (5976.43 m3/s) for volume and −4,463,045.58 kg.psu./s (185,827,573.35 kg.pau./s) for salt. The vertical structure of net volume and salt transport bot in Line-A and Line-B shows the water goes to outer bay in surface and inner bay in subsurface. While in the spring tide the surface deeper than neap tide. It indicated that water mass exchange dominantly influenced by river in surface and tidal in subsurface. It also shows that water mass from inner bay more easy flushing during spring tide than neap tide and vice versa

Production and Structural Parameters of the Phytoplankton and Bacterioplankton Communities at Two Stations in the Open Part of the Sevastopol Bay Mouth: Assessment of the Effect of the Mussel Farm

Production and Structural Parameters of the Phytoplankton and Bacterioplankton Communities at Two Stations in the Open Part of the Sevastopol Bay Mouth: Assessment of the Effect of the Mussel Farm

Optimization for Cost-Effectively Monitoring Ecological Effects of Water Diversion on the Urban Drinking Water Sources in a Large Eutrophic Lake

Due to the inputs of allochthonous pollutants and biological species from imported water, ecological effects of water diversion on urban drinking sources require long-term monitoring. Since spatial distributions of biological and environmental elements are always susceptible to water diversion, the monitoring specifications in water-receiving regions are always different from conventional ecological monitoring, especially in monitoring parameter selection and site distribution. To construct the method for selecting sensitive monitoring parameters and optimizing sites distribution in lakes, the large river-to-lake water diversion project, Water Diversion from Yangtze River to Lake Taihu in China, was taken as an example. The physicochemical properties and phytoplankton communities in the water-receiving Gonghu Bay and the referenced lake center were investigated and compared between the water diversion and non-diversion days in different seasons from 2013 to 2014. The comparative and collinearity analyses for selecting sensitive physicochemical parameters to water diversion, and the multidimensional scaling analysis based on the matrices of biological and sensitive physicochemical data, were integrated to optimize the monitoring in the water-receiving lake regions. Seven physicochemical parameters, including water temperature, pH, dissolved oxygen, total nitrogen, total phosphorus, chlorophyll a, and active silicate, were demonstrated to be sensitive to seasonal water diversion activities and selected for optimizing the site distribution and daily water quality monitoring. The nonmetric multidimensional scaling analysis results based on the data matrices of sensitive physicochemical parameters and phytoplankton communities were consistent for sites distribution optimization. For cost-effective monitoring, the sites distribution scheme could choose the optimizing results based on the Euclidean distance from 3.0 to 4.0 and the Bray-Curtis similarity from 40 to 60%. This scheme divided the Gonghu Bay into three water regions: the inflow river inlet, bay center, and bay mouth adjacent to the open water region. In each of the three regions, one representative site could be selected. If focusing on more details of each region, the standards with the Euclidean distance lower than 2.0 and the Bray-Curtis similarity higher than 60% should be considered. This optimization method provided an available way to fulfill the cost-effective long-term monitoring of urban drinking water sources influenced by water diversion projects.

Normal-incidence bottom loss measurements over a sand-mud gradient and comparison to direct seabed measurements

Seabed variability introduced by physical or biogenic processes contributes to multi-scale horizontal and vertical variability in seabed acoustic and geotechnical properties. An experiment was conducted near the mouth of Mobile Bay to investigate such spatial variability over a mud-sand gradient. A normal-incidence bottom loss survey was conducted on a 750 × 1500 m2 grid with 50-m track-line spacing, in which a broadband acoustic source transmitted frequency-modulated chirps (1–100 kHz) every second, resulting in dense sampling of the seabed reflection coefficient over a wide frequency band. Diver cores were collected in the survey area for direct analysis of near-surface seabed properties. Cores were acoustically logged to obtain vertical profiles of sound speed and attenuation (10–1000 kHz) and then analyzed for physical properties (porosity, grain size, carbon content), infauna community composition, and sediment strength properties. Additionally, in situ portable free fall penetrometer measurements were conducted within the survey area to characterize geotechnical properties within the upper 50 cm of the sediment. Spatial distributions of properties estimated from bottom loss measurements (e.g. porosity and sound speed) will be compared with vertical profiles from the cores and from the penetrometer to examine potential connections between seabed acoustic, geotechnical, and biological parameters. [Sponsored by ONR.]

The Effects of Hypoxia and Anthropogenic Disturbance on the Distribution, Abundance and Recruitment of the Sea Cucumber Holothuria leucospilota at the Mouth of a Subtropical Bay, China

Despite the commercial importance of the sea cucumberHolothuria leucospilotaincreasing in recent years, little is known of its spatial distribution and ecology in the South China Sea. We investigate the distribution, abundance, and recruitment ofH. leucospilotafrom 2017 to 2020 at two sites (S1 and S2) in Daya Bay, a typical subtropical bay which is strongly influenced by human activities in the South China Sea. We report hypoxia to driveH. leucospilotafrom deeper into shallower waters with higher DO concentrations at the mouth of Dapeng Cove in Daya Bay (S1), particularly during summer. Population size at S1 decreased by 90% from 2017 levels, before this area was opened to the public in 2018; recruitment was not observed by August (summer) of 2020. In contrast, in summers of 2017 and 2020,H. leucospilotaabundance at S2, a protected open-water area, increased by 84%, and the proportion of small-sized (recently recruited) sea cucumber in the population increased by 20%. Severe summer hypoxia at S1 could negatively influenceH. leucospilotaspawning and larval settlement, which combined with depletion of broodstock because of fishing pressure and/or hypoxia-induced mortality, could inhibit recruitment. In contrast, higher DO concentrations and abundant broodstock during summer (the breeding season) favoured recruitment ofH. leucospilotaat S2. Overall, hypoxia and anthropogenic disturbance impede recovery ofH. leucospilotaat S1, while at the protected S2, larvae may be released to settle in nearby areas. It is imperative to develop a better understanding of the biology, ecology and conservation of tropical sea cucumbers in China.

Surface-Layer Circulations in Suruga Bay Induced by Intrusions of Kuroshio Branch Water

The water mass structure in Suruga Bay is strongly influenced by open-ocean water. In particular, it is suggested that intermittent intrusions of the Kuroshio water generate characteristic circulations in the surface layer of the bay. In this study, we investigated the processes of the intrusions of open-ocean water into the bay and related generation of bay-scale cyclonic and anti-cyclonic circulation patterns. In doing so, we used an ocean simulation product with observational data constraint on meso and larger scales and with a resolution fine enough to resolve the smaller-scale intrusion structure. Cyclonic and anti-cyclonic circulation patterns as suggested by previous observational studies were detected as positive and negative first leading empirical orthogonal function (EOF) modes of the velocity field in Suruga Bay. The time scale of occurrences of these patterns was estimated as about 1 month, which was consistent with short-term Kuroshio fluctuations as reported in previous studies. Conditions favorable for generating these patterns were analyzed for three typical Kuroshio path periods individually. As suggested by previous studies, relatively strong northward flow to the west of Zeni-su generally promoted the open-ocean water intrusions into the eastern bay mouth, leading the cyclonic circulation in Suruga Bay. Our results showed that the correlation of this relation was significant for each Kuroshio path period. The open-ocean water intrusion increased the surface-layer temperature in Suruga Bay by about 0.7°C on average. On the other hand, the anti-cyclonic circulation pattern in Suruga Bay tended to be generated with relatively weak northward flow to the west of Zeni-su during the large meander Kuroshio path period, whereas this relation was rather weak during other periods. These results were mostly supported by available observations and would be useful for integrating our understanding of the influences of the western boundary current fluctuations on the circulation and temperature variations in proximal bays.

The Coastal Hydrodynamics Analysis in The Lampung Bay

The waves play a major role in the hydrodynamics of the sea, which they are very influential on human activities in the ocean. Thus, the knowledge of the waves conditions can provide many advantages, this is a challenge for marine experts in modeling ocean dynamics. The coastal area of Lampung Bay is one of the most densely populated areas in Bandar Lampung. The economic situation in the coastal area of Lampung Bay has been developing for a long time, this can be seen from the many old buildings in the coastal area. The existence of extreme waves in Lampung Bay can be as a concern for determining disaster mitigation planning and zoning around Lampung Bay. Based on the result of tidal analysis using the formzhal number equation, it is known that the type of tides in the research sites is mixed (semi-diurnal dominant) tidal type. According to simulating model of the wave characteristics in Lampung Bay, the sea characteristics can be divided into two, namely slight sea for deep waters of Lampung Bay with a wave height of 0 - 1.25 meters, and moderate sea for waters at the mouth of Lampung Bay with a wave heights of 1.25 - 2.5 meters.

Feeding habits and seasonal trophic guilds structuring fish community in the bay mouth region of a tropical estuarine habitat.

Understanding trophic relationships of fish in estuarine ecosystem is an important element for sustainable resource management. This study examined the feeding habits of 29 dominant fish species, characterized the trophic guilds, assessed the impact of season and clarified the role of diets in structuring the fish community in the mouth region of Pattani Bay, Thailand. Samples of 5792 fishes collected monthly by gillnets from March 2019 to February 2020 were used for stomach content analyses. It was found that the number of food types and fullness index differed between fish taxa (P < 0.001). Most fishes were specialist feeders feeding on specific food components and were categorized into five trophic guilds: piscivore, shrimp-fish feeder, polychaete feeder, zooplanktivore and planktivore. Six species were piscivorous, considered as apex predators, that fed almost entirely on fishes. High diet overlaps among some species (>0.6) were recorded. Not much variation in seasonal guilds was observed: four guilds in the dry season, three in the moderate rainy season and four in the rainy season. Some species remained in the same guild the whole year round, but some fishes changed seasonally. Two fish communities from different regions of the bay were segregated based on feeding habits. The inner bay community comprised mainly copepod and plankton feeders, but there were more piscivores in the deeper bay mouth area. Results from this study help us to understand the feeding habits and trophic guilds of dominant fish species at the mouth of this tropical estuarine bay.