Vietnamese Coast Research Articles

Three-dimensional structure of temperature, salinity, and Velocity of the summertime Vietnamese upwelling system in the South China Sea on the interannual timescale

Summertime upwelling system off the southern Vietnamese coast is one of the most essential oceanographic features in the South China Sea. This system is divided into two regions along the coast, the Southern Coastal Upwelling (SCU; south of 12.5°N) and Northern Coastal Upwelling (NCU; north of 12.5°N), and one in the offshore area, the Offshore Upwelling (OU; east of 110°E). Utilizing the HYCOM ocean reanalysis product in the period of 1994–2015, vertical characteristics of this upwelling system on the interannual timescale are investigated. Furthermore, the omega equation is applied to reconstruct vertical velocity to quantify its intensity and clarify the corresponding leading factors in the three regions. The analysis indicates that the kinematic deformation effect is the primary contributor to coastal upwelling formation while the momentum effect plays the leading role in offshore upwelling. The SCU variability is more sensitive to the momentum effect; however, in the NCU, the kinematic deformation effect is offset by the momentum effect and the upwelling is enhanced as the kinematic deformation (momentum) effect increases (decreases). The summertime mean vertical velocities in the central areas of SCU, NCU, and OU are estimated at 0.16 m/d, −0.08 m/d, and 0.003 m/d, respectively. The vertical velocity speeds up to 0.32 m/d, 0.07 m/d, and 0.08 m/d as the strong upwelling event occurs.

Organophosphate esters and their metabolites in silver pomfret (Pampus argenteus) of the Vietnamese coastal areas: Spatial-temporal distribution and exposure risk

A large number of studies on organophosphate esters (tri-OPEs) in marine organisms have not assessed the simultaneous occurrence of tri-OPEs and their metabolites (di-OPEs) in these species. This research investigated the concentration and geographical distribution of 15 tri-OPEs and 7 di-OPEs in 172 samples of Pampus argenteus that were collected annually from 2021 to 2023 at three distinct locations along the Vietnamese coast. As a result, tri-OPEs and di-OPEs were detected in numerous fish samples, indicating their widespread spatial and temporal occurrence in marine fish and pointing out the importance of monitoring their levels. The tri-OPEs and di-OPEs ranged within 2.1–38.9 ng g−1 dry weight (dw) and 3.2–263.4 ng g−1 dw, respectively. The mean concentrations of tri-OPEs ranged from 0.4 (TIPrP) to 5.4 ng g−1 dw (TBOEP), with TBOEP and TEHP having the highest mean values. In addition, the profiles of tri-OPEs in fish exhibited a descending order: Σalkyl OPEs > ΣCl-alkyl OPEs > Σaryl OPEs. The di-OPEs, namely BEHP and DMP, had the highest mean levels, measuring 33.4 ng g−1 dw and 23.8 ng g−1 dw, respectively. Furthermore, there have been significant findings of strong positive correlations between di-OPEs and tri-OPE pairs (p < 0.05). It is worth noting that there is a noticeable difference in the composition of tri-OPEs between the North and other regions. Despite these findings, the presence of OPE-contaminated fish did not pose any health risks to Vietnam's coastal population.

Simulate the current dynamics process and predict the trajectory of plastic waste flowing out to sea from estuaries in the Gulf of Tonkin

This paper presents the results of a numerical simulation of flow dynamics in the northern Vietnam Sea. Based on these results, the trajectories of plastic waste from river mouths in the northern Vietnam Sea are predicted. The numerical simulation is based on the ROMS model for the northern Vietnam Sea and surrounding areas, in combination with data collected from a Vietnam-France international cooperation project (Study, evaluation, and prediction of the transport and dispersion of small plastic waste in the Van Uc River mouth area). The dynamic regime of the study area is considered to simulate the main wind seasons. The results show that the flow field in the Northern Vietnam Sea follows the tidal phases. In the rising tide phase, the general trend is for the flow to move from the south to the north. Conversely, in the falling tide phase, the general trend is for the flow to move from the north to the south. The flow speed in the tidal phases is largest at about 65-70 cm/s and smallest at about 5-10 cm/s. The much larger surrounding area outside the Northern Vietnam Sea has a very complex flow field, with many different flow areas and vortices. There is a belt of vortices that extends for hundreds of kilometers, with an average flow speed that is higher than the flow in the Northern Vietnam sea. Based on the flow field and the frequency of occurrence in the area near the Vietnamese coast where rivers flow out, the frequency of flow flowers are used to predict the trajectories of plastic waste from river mouths into the sea. The results of the calculations and predictions, when compared with the actual data, show good agreement.

Endocrine-disrupting chemicals in Vietnamese marine fish: Occurrence, distribution, and risk assessment

The release of endocrine-disrupting chemicals (EDCs) into the aquatic environment, specifically the oceans, is increasing, leading to adverse effects on the marine ecosystem. Using optimized QuEChERS extraction methods, the study created the first contamination profiles of 44 EDCs, including organic ultraviolet compounds, pharmaceutically active compounds, hormones, and phthalate esters, in 114 fish muscle samples from five species collected along the Vietnamese coast. The study found that largehead hairtail exhibited the highest total EDCs at 208.3 ng g−1 lipid weight (lw), while Indian catfish displayed the lowest concentration at 105.5 ng g−1 lw. Besides, the study observed notable variations in the total EDCs across distinct fish species. This study hypothesized that the marine economic characteristics of each research location have a significant role in shaping the pollution profile of EDCs found in fish specimens taken from the corresponding area. As a result, a notable disparity in the composition of organic ultraviolet compounds has been observed among the three regions of North, Central, and South Vietnam (Mann-Whitney U test, p < 0.05). Despite these findings, EDC-contaminated fish did not pose any health risks to Vietnam's coastal population.

Quality index method to evaluate the quality of Jinga shrimp (&lt;i&gt;Metapenaeus affinis&lt;/i&gt; L.) preserved in ice water

The Quality Index Method (QIM) provides a quick and accurate quality assessment. It makes it possible to calculate preserving time and establish the freshness of sea food. This article introduces a quality assessment program based on the QIM scheme and quality index (QI) for the Jinga shrimp.&#x0D; The research included Jinga shrimps (Metapenaeus affinis L.), a commercially valuable aquatic species widely distributed throughout the Vietnamese coast. The input data included the changes in appearance and sensory profile of sampled shrimps during 20 days of storage at 0–4°C in ice water.&#x0D; They were used to construct a QIM scale, which was applied to other shrimp samples at different storage time to evaluate the relationship between the QI score and the storage time. After that, the QIM scale was tested on ten random shrimp samples to verify its shelf-life predictive power. This study managed to establish a correlation equation between the QI scores and the storage time with the coefficient of R2= 0.97. This correlation proved highly reliable as verified by comparing the predicted and actual best shelf life of Jinga shrimps stored in ice water for 8–10 days.&#x0D; The QIM program provides a practical and effective science-based tool that delivers fast and reliable results for customers, fishermen, food traders, and aquacultural enterprises.

Temperature as a factor controlling geographical distribution of greenNoctiluca scintillansin Southeast Asia

AbstractThe dinoflagellate Noctiluca scintillans exists in two forms, green and red Noctiluca, with and without the photosynthetic endosymbiont Pedinomonas noctilucae, respectively. In Southeast Asia, green Noctiluca has a northern boundary of distribution in the Luzon Strait and the Vietnamese coast, approximately corresponding to the 25°C isotherm. We examined whether this boundary arose from the growth dependence of Noctiluca on temperature and/or that of P. noctilucae. We analyzed the effect of temperature on growth by examining one and four unialgal cultures of red and green Noctiluca, respectively, and two monocultures of the endosymbiont. Growth dependence on temperature was markedly different between host cells of green Noctiluca and monocultures of the endosymbiont, although some variations in growing temperature were observed among strains of both Noctiluca and the endosymbiont. Green Noctiluca grew at a temperature range of 20–31°C, whereas P. noctilucae did not grow at low temperatures ≤25°C. Growth rates of green Noctiluca were considerably higher when fed compared to monocultures. Our findings demonstrate that the effect of temperature on P. noctilucae growth is a crucial factor controlling the geographical distribution of green Noctiluca in the South China Sea. An implication of this finding is discussed in the context of global warming.

Marine Floral Biodiversity, Threats, and Conservation in Vietnam: An Updated Review.

Part of the Indo-Chinese peninsula and located on the northwest edge of the Coral Triangle in the South China Sea, the Vietnamese coastal zone is home to a wealthy marine biodiversity associated with the regional geological setting and history, which supports a large number of marine ecosystems along a subtropical to tropical gradient. The diversity of coastal benthic marine primary producers is also a key biological factor supporting marine biological diversity. The present review provides: (1) an updated checklist of the Vietnamese marine flora, (2) a review of molecular-assisted alpha taxonomic efforts, (3) an analysis of marine floral biodiversity spatial distribution nationally and regionally (South China Sea), (4) a review of the impact of anthropogenic and environmental stressors on the Vietnamese marine flora, and (5) the efforts developed in the last decade for its conservation. Based on the studies conducted since 2013 and the nomenclatural changes that occurred during this period, an updated checklist of benthic marine algae and seagrasses consisted in a new total of 878 species, including 439 Rhodophyta, 156 Ochrophyta, 196 Chlorophyta, 87 Cyanobacteria, and 15 phanerogam seagrasses. This update contains 54 new records and 5 new species of macroalgae. The fairly poor number of new records and new species identified in the last 10 years in a "mega-diverse" country can be largely attributed to the limited efforts in exploring algal biodiversity and the limited use of genetic tools, with only 25.4% (15 species) of these new records and species made based on molecular-assisted alpha taxonomy. The South Central Coast supports the highest species diversity of marine algae, which coincides with the largest density of coral reefs along the Vietnamese coast. Vietnam holds in the South China Sea one of the richest marine floras, imputable to the country's geographical, geological, and climatic settings. However, Vietnam marine floral biodiversity is under critical threats examined here, and current efforts are insufficient for its conservation. A methodical molecular-assisted re-examination of Vietnam marine floral biodiversity is urgently needed, complemented with in-depth investigations of the main threats targeting marine flora and vulnerable taxa, and finally, conservation measures should be urgently implemented.

Intraseasonal variability of the South Vietnam upwelling, South China Sea: influence of atmospheric forcing and ocean intrinsic variability

Abstract. The South Vietnam upwelling (SVU) develops off the Vietnamese coast (South China Sea, SCS) during the southwest summer monsoon over four main areas: the northern coastal upwelling (NCU), the southern coastal upwelling (SCU), the offshore upwelling (OFU) and the shelf off the Mekong River mouth (MKU). An ensemble of 10 simulations with perturbed initial conditions were run with the fine-resolution SYMPHONIE model (1 km inshore) to investigate the daily to intraseasonal variability of the SVU and the influence of the ocean intrinsic variability (OIV) during the strong SVU of summer 2018. The intraseasonal variability is similar for the SCU, MKU and OFU, driven to the first order by the wind variability. The MKU and SCU are induced by stable ocean dynamics (the northeastward then eastward boundary current) and have very little chaotic variability. The OIV has a stronger influence on OFU. In July, OFU mainly develops along the northern flank of the eastward jet. The influence of the OIV is strongest and related to the chaotic variability of the meridional position of the jet. In August, this position is stable and OFU develops mainly in the area of positive wind curl and cyclonic eddies north of the jet. The influence of the OIV, weaker than in July, is related to the organization of this mesoscale circulation. The NCU shows a behavior different from that observed in the other areas. In the heart of summer, a large-scale circulation formed by the eastward jet and eddy dipole is well established with an alongshore current preventing the NCU development. In early and late summer, this circulation is weaker, allowing a mesoscale circulation of strongly chaotic nature to develop in the NCU area. During those periods, the OIV influence on the NCU is very strong and related to the organization of this mesoscale circulation: the NCU is favored (annihilated) by offshore-oriented (alongshore) structures.

Wave Regime of Vietnamese Waters on the Basis of Numerical Modeling and Field Measurements

This paper presents results of research of the wave regime in Vietnamese waters (South China Sea) based on the data of numerical modeling data using the WAM model (WAVE Modeling). The model domain covers the basin of the South China Sea (SCS). The bathymetry of the SCS used in the model is based on the ETOPO5 digital database. Wind parameters are based on the six-hour NCEP/NCAR reanalysis data with a resolution of ΔX = ΔY = 0.25° over the period 1979–2021. The field wave data measurements were collected by the Institute of Oceanography of Vietnam Academy of Science and Technology in the southern central Vietnamese waters in 2013. The statistical data of computed wave characteristics for the period of 43 years (1979–2021) illustrate that the main wave direction in Vietnamese waters was NE during the Northeastern (NE) monsoon, and in the opposite direction during the Southwestern (SW) monsoon. The NE monsoon wave was more dominant than that of the SW monsoon wave. Recurrence frequency (%) of significant wave height Hs &gt;1.0 m (Hs – significant wave height is an average of 1/3 the largest of serial waves relative to average seawater level) greater than 50%&#x0D; covered the northeastern, central region of the SCS, and central Vietnamese coast. The wave recurrence frequency in the Gulf of Tonkin and Gulf of Thailand was &lt;40% and &lt;30%, respectively. The central Vietnamese coast from Ly Son Island to Phu Quy Island was the strongest affected by wave action. The recurrence frequency of the maximum significant wave height Hs &gt;3.5 m was greater than 1.5%. The Gulf of Tonkin (Bach Long Vi Island) and the Gulf of Thailand (Tho Chu Island) were less affected by&#x0D; wave action than the central Vietnamese coast: the recurrence frequency of the maximum wave height (Hs&gt;3.5 m) was less than 0.1%. Phu Quy and Con Dao Islands were more influenced by wave action during both seasons than the central coast of Vietnam.

Assessment of relative dispersion in the Gulf of Tonkin using numerical modeling and HF radar observations of surface currents

Particle pair statistics from synthetic drifter trajectories reconstructed from realistic, high-resolution numerical simulations (SYMPHONIE model) and HF radar velocity measurements are used to investigate the dispersion properties in the Gulf of Tonkin (GoT). This study takes an approach based on two-particles statistics providing the relative dispersion, relative diffusivity and Finite Size Lyapunov Exponent (FSLE) estimates. In the GoT, the relative dispersion follows the predictions from the theory of two-dimensional turbulence with two inertial subranges identified in the kinetic energy spectrum with the spectral slopes −5/3 and −3. The time evolution of dispersion shows an exponential growth during 5–8 days, followed by a power law regime during the next 6–20 days. Fixed-length indicators from the relative diffusivity and the FSLE reveal a local dispersion at large and intermediate scales (above Rossby radius of deformation) and non-local dispersion in sub-mesoscale range (below Rossby radius of deformation). The effect of river runoff on the local hydrodynamics and dispersion processes is assessed using the numerical model simulations without river discharge. The results show that in the model, the river plume, when present, highly impacts the Lagrangian statistics. High gradients of buoyancy reinforce the sub-mesoscale circulation in a large region along the Vietnamese coast and modify the scales and intensity of turbulent dispersion. However, a clear change of dispersion regime in the sub-mesoscale range is not identified, suggesting that the mesoscale circulation in the GoT largely governs particle spreading even at small scale.

State of the Vietnamese Coast—Assessing Three Decades (1986 to 2021) of Coastline Dynamics Using the Landsat Archive

Vietnam’s 3260 km coastline is densely populated, experiences rapid urban and economic growth, and faces at the same time a high risk of coastal hazards. Satellite archives provide a free and powerful opportunity for long-term area-wide monitoring of the coastal zone. This paper presents an automated analysis of coastline dynamics from 1986 to 2021 for Vietnam’s entire coastal zone using the Landsat archive. The proposed method is implemented within the cloud-computing platform Google Earth Engine to only involve publicly and globally available datasets and tools. We generated annual coastline composites representing the mean-high water level and extracted sub-pixel coastlines. We further quantified coastline change rates along shore-perpendicular transects, revealing that half of Vietnam’s coast did not experience significant change, while the remaining half is classified as erosional (27.7%) and accretional (27.1%). A hotspot analysis shows that coastal segments with the highest change rates are concentrated in the low-lying deltas of the Mekong River in the south and the Red River in the north. Hotspots with the highest accretion rates of up to +47 m/year are mainly associated with the construction of artificial coastlines, while hotspots with the highest erosion rates of −28 m/year may be related to natural sediment redistribution and human activity.

Distribution features of the weather conditions in Nha Trang Bay (The South China Sea)

Nha Trang Bay is a semi-envelop coastal basin. It is located on the west coast of the South China Sea as well as in the south of the central part of the Vietnamese coast. The climate of the bay belongs to the sub-equatorial zone or to the zone of equatorial-tropical monsoons. Determination of the meteorological characteristics of an ocean region, especially for nearshore bay waters, plays a very important role in the sustainable development of the social-economical system of Vietnam. This paper presents a spatial and temporal long-term analysis of several meteorological characteristics in Nha Trang Bay, such as wind, tropical cyclones, air temperature, air humidity, and rainfall. The meteorological data were collected from the Nha Trang meteorological station during 1977–2015 (wind data until 2020).&#x0D; The data for typhoons were extracted from the National Weather Service (USA) and the Japan Meteorological Agency during 1945–2015. Statistical methods for collecting and analyzing data to estimate the statistical parameters of meteorological characteristics were used in the study.&#x0D; A study of results shows that the meteorological characteristics in the Nha Trang Bay are a seasonal variation of the East Asian monsoon (northeastern-NE and southwestern-SW monsoons).&#x0D; The winds in Nha Trang Bay are the seasonal change, influenced by the NE monsoon from October to April and the SW monsoon from June to August. May and September are the transition periods.&#x0D; Nha Trang Bay has a temperate tropical climate because the temperature regime of the bay ranges from less than 25°C in the winter and more than 28°C in the summer.&#x0D; Extreme conditions, including typhoon activity and heavy rainfall (coinciding with high humidity), occurred in October, November, and December.

First faunal record of larval and juvenile gobies (Actinopterygii: Gobiiformes) in the Ka Long estuary, northern Vietnam

Gobies are dominant in terms of both species diversity and abundance in estuarine habitats, but little is known about their early developmental stages in the coastal waters of Vietnam. To examine species diversity of goby larvae and juveniles, monthly collections were carried out using a small seine net from the Ka Long estuary in the northernmost Vietnamese coast, from September 2014 to August 2015. A total of 1,334 goby fishes of 20 species or more in three families (Butidae, Oxudercidae and Gobiidae) were caught, including nine unidentified species. This is the first record of gobies at early developmental stages from an estuary in Vietnam. The family Oxudercidae was the most abundant in terms of total species, and Gobiopterus chuno was the most frequent species in the study area. The goby specimens collected were mostly postflexion larvae and juveniles, ranging from 2.3 mm to 99.1 mm in body length. The size of nine dominant gobies was around 10 mm body length. In the study site, goby fishes are from tropical, subtropical and temperate zones, suggesting this goby fauna can display transitional biodiversity from tropical to temperate waters.

Variability of the Red River Plume in the Gulf of Tonkin as Revealed by Numerical Modeling and Clustering Analysis

We study the daily to interannual variability of the Red River plume in the Gulf of Tonkin from numerical simulations at high resolution over 6 years (2011–2016). Compared with observational data, the model results show good performance. To identify the plume, passive tracers are used in order to (1) help distinguish the freshwater coming from different continental sources, including the Red River branches, and (2) avoid the low salinity effect due to precipitation. We first consider the buoyant plume formed by the Red River waters and three other nearby rivers along the Vietnamese coast. We show that the temporal evolution of the surface coverage of the plume is correlated with the runoff (within a lag), but that the runoff only cannot explain the variability of the river plume; other processes, such as winds and tides, are involved. Using a K-means unsupervised machine learning algorithm, the main patterns of the plume and their evolution in time are analyzed and linked to different environmental conditions. In winter, the plume is narrow and sticks along the coast most of the time due to the downcoast current and northeasterly wind. In early summer, the southwesterly monsoon wind makes the plume flow offshore. The plume reaches its highest coverage in September after the peak of runoff. Vertically, the plume thickness also shows seasonal variations. In winter, the plume is narrow and mixed over the whole water depth, while in summer, the plume can be detached both from the bottom and the coast. The plume can deepen offshore in summer, due to strong wind (in May, June) or specifically to a recurrent eddy occurring near 19°N (in August). This first analysis of the variability of the Red River plume can be used to provide a general picture of the transport of materials from the river to the ocean, for example in case of anthropogenic chemical substances leaked to the river. For this purpose, we provide maps of the receiving basins for the different river systems in the Gulf of Tonkin.

Tonkin Gulf and the Escalation of the Vietnam War

Tonkin Gulf and the Escalation of the Vietnam War

Impacts of Wind and Current on the Interannual Variation of the Summertime Upwelling Off Southern Vietnam in the South China Sea

AbstractSummertime upwelling off the southern Vietnamese coast is one of the most essential oceanographic features in the South China Sea. Based on analyzing the 38‐year (1982–2019) sea surface temperature (SST) images, locations of summertime Vietnamese upwelling centers are found to be classified into three sub‐regions: the Southern Coastal Upwelling (SCU; south of 12.5°N), the Northern Coastal Upwelling (NCU; north of 12.5°N), and the Offshore Upwelling (OU; east of 110°E). Variations of upwelling intensities in the three sub‐regions are further quantified via an adaptive SST‐based upwelling index, and possible processes relevant to wind field (including wind stress and its curl) and currents are, respectively, proposed. The analyses show that the local along‐shore wind stress, inducing offshore Ekman transport, can produce the coastal upwelling‐favorable condition but is not the only one of main factors in controlling the interannual variability of the coastal upwelling. The enhancement of wind stress curl dipole off the southern Vietnamese coast, which accompanies the scaling up of the double‐gyre structure east of Vietnam and results in the reinforcement and southward shift of eastward‐flowing jet, and the exaggeration of the cyclonic gyre‐associated southward along‐shore current are responsible for the intensification of upwelling in the SCU, but suppress the development of upwelling in the NCU. The well‐developed double‐gyre structure serves as the essential condition for the OU occurrence and the OU is much more sensitive to the change of cyclonic gyre to the north of the jet.

Abrupt change in Vietnam coastal upwelling as a response to global warming

ABSTRACTCoastal upwelling is of great social and economic significance to the human community. The Vietnam coastal upwelling is a fundamental part of upwelling systems in the South China Sea, western Pacific Ocean. However, its sedimentary response to global warming has been largely unknown. Here we reconstruct a 3200‐year sedimentary record based on high‐resolution geochemical analyses of a marine core from off the Vietnamese coast. The results reveal an abrupt sedimentary change since approximately 1950 ce. The abrupt change is explained by concurrent rapid intensification of the coastal upwelling. This can be ascribed to significant global change since the beginning of the 20th century. Global warming could enhance wind speed during the summer and strengthen the coastal upwelling. The forced upwelling results in an increase in nutrient availability and marine primary production; however, ongoing global warming may also increase the risk of more frequent algal blooms in this area.

Mapping Submerged Aquatic Vegetation along the Central Vietnamese Coast Using Multi-Source Remote Sensing

Submerged aquatic vegetation (SAV) in the Khanh Hoa (Vietnam) coastal area plays an important role in coastal communities and the marine ecosystem. However, SAV distribution varies widely, in terms of depth and substrate types, making it difficult to monitor using in-situ measurement. Remote sensing can help address this issue. High spatial resolution satellites, with more bands and higher radiometric sensitivity, have been launched recently, including the Vietnamese Natural Resources, Environment, and Disaster Monitoring Satellite (VNREDSat-1) (V1) sensor from Vietnam, launched in 2013. The objective of the study described here was to establish SAV distribution maps for South-Central Vietnam, particularly in the Khanh Hoa coastal area, using Sentinel-2 (S2), Landsat-8, and V1 imagery, and then to assess any changes to SAV over the last ten years, using selected historical data. The satellite top-of-atmosphere signals were initially converted to radiance, and then corrected for atmospheric effects. This treated signal was then used to classify Khanh Hoa coastal water substrates, and these classifications were evaluated using 101 in-situ measurements, collected in 2017 and 2018. The results showed that the three satellites could provide high accuracy, with Kappa coefficients above 0.84, with V1 achieving over 0.87. Our results showed that, from 2008 to 2018, SAV acreage in Khanh Hoa was reduced by 74.2%, while gains in new areas compensated for less than half of these losses. This is the first study to show the potential for using V1 and S2 data to assess the distribution status of SAV in Vietnam, and its outcomes will contribute to the conservation of SAV beds, and to the sustainable exploitation of aquatic resources in the Khanh Hoa coastal area.

Utilization of Industrial Waste in Cement in a Marine Environment with a Tropical Climate

This novel study on cement paste material was conducted with the aim of keeping up with the rapid development of urban construction and contributing to the continuous improvement of building materials to overcome environmental issues. In this study, several kinds of industrial waste were used to enhance the properties of cement paste for application in a marine environment with a tropical climate, such as in Vietnam. This study focuses on evaluating the properties of cement paste containing cement replacement combining 0–30% fly ash, 0–10% silica fume, and plasticizer accounting for 0.3% and 0.4% of the binder by mass. Water demand, chloride ion and sulfate ion permeability, and microstructural properties of the cement paste were determined by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscope (SEM) and they were investigated after 28 and 56 days. The test results show that an optimum mixture could be obtained with the use of 20% fly ash, 10% silica fume (replacing Portland cement), and 0.4% plasticizer. The application of such materials to sea dikes affected by a tropical climate (characterized by heat, humidity, salty seawater, many big storms, large waves, and strong tides) was investigated for four years on the Vietnamese coast. The test results indicate that fly ash and silica fume can improve the corrosion and abrasion resistance of concrete in coastal areas with a tropical climate, such as in Vietnam.

Description of Three New Species of Rhadinorhynchus Lühe, 1911 (Acanthocephala: Rhadinorhynchidae) from Marine Fish off the Pacific Coast of Vietnam.

Of the 43 valid species of Rhadinorhynchus Lühe, 1911, 20 species are now known from the Pacific Ocean off Australia, Japan, and Vietnam. We have already described over 50 species and higher taxa from the Pacific Ocean off Vietnam over the last 15years. The present research is a continuation of our efforts to taxonomically map new acanthocephalan taxa, especially from Vietnam. Some of our collections in 2016 and 2017 revealed the presence of new species of the genus Rhadinorhynchus from various species of marine fish off the Pacific coast of Vietnam. We provide descriptions of these new species here. Standard methods of collection and examination of marine hosts, processing and illustrating of specimens, and taxonomic identification of parasites using the extensive collections of the lead author were used. Type specimens were deposited at the Harold W. Manter Lab. collection, Lincoln, Nebraska. Three species Rhadinorhynchus are described from marine fish off the Vietnamese coast. Rhadinorhynchus circumspinus n. sp. with fusiform trunk, 1 field of anterior trunk spines, and anteriorly globular proboscis with up to 21 dorsoventrally differentiated hooks in 17-18 rows is described from Triacanthus biaculeatus Bloch (Triacanthidae) off Hai Phong. Rhadinorhynchus pacificus n. sp. with cylidrical trunk and proboscis with up to 25 dorso-ventrally similar hooks in 14-18 rows and trunk spines in 2 fields of dorsal, ventral and lateral spines is described from Auxis thazard (Lacepède) and Auxis rochei (Lacepède) (Scombridae) off Nha Trang. Rhadinorhynchus multispinosus n. sp. with cylindrical trunk and proboscis with up to 32 dorso-ventrally differentiated hooks in 12 rows, and many trunk spines in 2 fields of dorsal, ventral and lateral spines is described from Decapterus maruadsi (Temminck and Schlegel) (Carangidae) also off Hai Phong. Rhadinorhynchus polynemi Smales, 2014 of Australia is not the Indian species (with smallest basal hooks) as the basal hooks are largest and is now named Rhadinorhynchus australis nom. nov. (=Rhadinorhynchus polynemi Smales, 2014). Rhadinorhynchus trivandricus George and Nadakal, 1978 with smallest basal hooks and 8 pyriform cement glands is relegated to genus Indorhynchus Golvan, 1969. With the description of these 3 new species, the numner of valid species of Rhadinorhynchus has now increased to 46. We include a new generic diagnosis to accommodate the increased knowledge of variability within this genus.