Vietnam Journal of Marine Science and Technology

Localized wind model of Weibull distribution in Vung Tau, Vietnam

Van Chung Tran — 2025-03-31

The wind data set of 10 m on the sea surface is provided by Vung Tau Meteorological Station for 2011–2022, with a frequency of 6 h. The purpose of this paper is to find the most effective parameters, that are scale parameter ‘c’ and shape parameter ‘k’ for the Weibull distribution for the wind regime in Vung Tau based on analyzing and comparing the efficiency of ten numerical methods, namely, the empirical method of Justus (EMJ), the empirical method of Lysen (EML), the method of moments (MoM), the graphical method (GM), the Mabchour’s method (MMab), the energy pattern factor method (EPFM), the maximum likelihood method (MLM), the modified maximum likelihood method (MMLM), the equivalent energy method (EEM), and the alternative maximum likelihood method (AMLM). According to the analysis results, the MLM method is best suited for the wind regimes from February to December; MLM and EMJ methods is best suited for January wind regimes; The AMLM, MLM, and EML methods are best suited for the wind regime in December the MLM and EMJ methods are best suited for November. The MMab method could result in inaccurate forecasting of the wind regime in the Vung Tau area.

Assessing the applicability of sentinel-2 remote sensing data to determine the bathymetry of a shallow coastal area: case study of Nhat Le Estuary, Quang Binh Province

Duc Hanh Le — 2025-03-31

Seabed mapping is complex and expensive because it is often performed in a harsh environment sensitive to weather factors. To overcome these limitations, there have been many studies on the application of remote sensing data to measure the seabed depth based on physical laws about the attenuation of reflected energy of light when passing through a water column. The value of reflected energy from the seabed on remote sensing images is used to determine the depth of the seabed. Worldwide, studies have been conducted on applying remote sensing data to measure seabed depth through the modeling and GEE cloud computing platforms. There are also studies in Vietnam that map the seabed topography for offshore islands. This paper measured the seabed depth based on experimental data, survey lines conducted in April and October 2018, and Sentinel 2 remote sensing images data for Nhat Le estuary area. The paper aims to review and evaluate the correlation and accuracy of the application of Sentinel-2 remote sensing image data to measure the depth of the seabed topography for shallow coastal waters. The results show that the correlation coefficient R² along the surveyed lines is from 0.84 to 0.94, and the mean RMSE ranges from 0.70 to 0.74. The above assessment shows that surveyed lines that can be employed to interpret a larger area in the same satellite image scene using the empirical formula in the study area. The formula can also be used to determine the depth of bottom topography for other geographical areas with similarities in seawater turbidity and bottom material, as well as technical issues.

Application of GIS and remote sensing in detecting coastal reclamation in the coastal areas of Hai Phong - Ha Long from 1990 to 2020

Thi Thu Huong Do — 2025-03-31

Coastal reclamation transforms coastal areas into usable land for urban, agricultural, and industrial purposes. This study evaluates the status of coastal reclamation from 1990 to 2020 in the Hai Phong - Ha Long coastal area using high and medium-resolution satellite images and GIS techniques. The findings revealed a significant increase in reclamation activity, with 900 hectares reclaimed in 1990–2000, 3,161 hectares in 2000–2010, and 3,434 hectares in 2010–2020. Over different periods, the objectives of reclamation activities shifted. In 1990-2000 and 2000–2010, the focus was primarily on facilitating aquaculture and mangrove cultivation. However, from 2010 onwards, the focus shifted to the developing industrial parks, urban areas, and recreational spaces. Coastal reclamation activities have led to changes in the coastline’s characteristics, including length and shape alterations. Over 30 years, the total coastline length has increased by 58.4 km, with the proportion of artificial coastlines increasing by 33.5%. Additionally, coastal reclamation has converted significant areas of mangrove forests, tidal flats, and shallow coastal waters into new land. Therefore, strong policies and integrated coastal zone management are needed to ensure sustainable development and preserve coastal ecosystems.

Diversity of dinoflagellates in the Northern Vietnam coastal waters

Van Thuoc Chu — 2025-03-31

Phytoplankton were investigated within the framework of the Vietnam’s coastal water quality monitoring program. The present study analyzed phytoplankton samples collected in the northern Vietnam coastal waters (Tra Co, Cua Luc, Do Son, Ba Lat, Sam Son and Cua Lo stations) from 2019 to 2022 to characterize diversity and abundance of dinoflagellate communities. A total of 129 species belonging to 35 genera, 23 families, 8 orders, and 2 classes of dinoflagellates were recorded in this study area. The diversity of dinoflagellates varied depending on the sampling locations and times. Tripos furca was recorded as the most dominant and common species (accounting for approx. 93% of the samples) in the dinoflagellate communities throughout the year. The density of dinoflagellates and Tripos furca varied strongly by sampling locations, times, and tides. This species seems preferable and grows with high density in the study area from June to September. Among water environment factors, salinity had the strongest correlation with the density of Tripos furca depending on the sampling locations and the tides.

Some growth characteristics of yellow-mouth turban shell (Turbo chrysostomus) in Ly Son Islands - Quang Ngai Province

Thai Tuyen Hua — 2025-03-31

Focusing on the species Turbo chrysostomus, the study examined aspects of distribution, growth characteristics and resource management strategies. Turbo chrysostomus mainly inhabits low water areas to coral reefs with a depth of 8 meters. The average Turban Shell height is 47.51 mm. The theoretical maximum size is 76.9 mm with growth factor K = 1.17, and the monthly growth rate in the first year is 5.36 mm. The correlation between the height (H) and weight (Wm) of the snail is H = -0.001*Wm + 0.8822. Notably, its growth pattern is uneven, with height increasing faster than weight. Worryingly, wild mussel populations are showing signs of decline, requiring resource management measures. Proposed solutions include eliminating the capture of small snails and avoiding development in key breeding areas, particularly Chua Hang and Hang Cau, to ensure the sustainability of the snail resource into the future.

Screening antimicrobial activities of actinomycetes raw extracts from marine ecosystems of Nha Trang and Van Phong Bay, Khanh Hoa Province

Thi Hong Minh Le — 2025-03-31

Marine actinomyces’ enormous genetic and functional diversity of has led scientist to search for potential secondary metabolite. Among the producers of important natural bioactive compounds discovered, actinomycetes are known to be efficient secondary metabolites with a broad spectrum of biological activities, such as antimicrobial, anticancer, and enzymes. The primary purpose of this study was to isolate and screen for antibacterial activity of potential actinomycete from marine ecosystems of Nha Trang and Van Phong Bay, Khanh Hoa Province, located in the middle-south of Vietnam. The marine actinomycete strains were characterized, and the ethyl acetate extracts were screened for antimicrobial activities using the microtiter broth dilution method. Out of which, the best MIC was produced by G112 and C011 strains. The lowest MIC values result in 16 µg/mL. G112 showed a zone of inhibition against four bacteria and Candida albican. C011 exhibited three different bacterial pathogens. The morphology and genetic results indicated that strain G112 belongs to Streptomyces species, and C011 was identified as a member of Pseudonocardia genus.

Water quality of submarine caves and marine karst lakes in Cat Ba Archipelago (Hai Phong, Vietnam)

Thi Thu Trang Cao — 2025-03-31

Submarine caves and marine karst lakes in the Cat Ba archipelago (Hai Phong) were surveyed in June and November, 2019. The results showed that the water was weakly alkaline, the dissolved oxygen concentration was very low, most of the oxygen saturation in the water was in the range of 50–70%. Water in submarine caves had higher and more stable salinity than that in marine karst lakes, however, the dissolved oxygen concentration was lower than that in lakes. The self-purification of water was better in the rainy season. The water was polluted by ammonium in the rainy season in Ang Vem, Ba Man, Ba Mat and Ang Gay lakes. There is no evidence of organic contamination but the high nitrate and phosphate concentration had been recorded. The presence of H₂S gas in the water had begun to affect organisms.

Development of a water quality index to assess and classify water quality in the coastal waters of Hai Phong (Vietnam)

Van Nam Le — 2025-03-31

The method of developing the water quality index (WQI) to evaluate and classify the water quality of the coastal waters of Hai Phong (2019) includes the following steps: selecting parameters, calculating sub - indices, determining weights, calculating the WQI, building a classification scale, and testing the formula. The water quality of Hai Phong’s coastal waters varied widely, ranging from very poor to excellent. The water quality of Hai Phong's coastal waters tended to improve from the river mouths to the sea. In the rainy season, the areas with very poor and poor water quality tended to expand, while the areas with medium and good water quality tended to shrink compared to the dry season. The area of excellent water quality showed little seasonal variation. During high tide, water quality was typically better than during low tide. The water quality at the Bach Dang, Lach Tray, Van Uc, and Thai Binh estuaries was very poor during low tide (WQI from 19 to 22) and poor during high tide (WQI from 43 to 45) in both the dry and rainy seasons. The South - Southwest area of the Hai Phong coastal estuary generally had worse water quality compared to the North and Northeast areas. The Ben Beo area (the main port of Cat Ba Island, where most of the island's large and small boats gathered) had medium water quality (WQI from 62 to 73). This area was at a higher risk of environmental pollution compared to other areas in the Cat Ba Island sea. The outside area had water quality ranging from good to excellent.

Hydrodynamic characteristics of Khor Al-Zubair Channel, Southern Iraq

Ali — 2025-03-31

The hydrodynamic features of the Khor Al-Zubair, a mixed, predominantly semidiurnal tidal channel situated in Southern Iraq at the northwest tip of the Arabian Gulf, were investigated using in situ measurements taken in 2015. The data utilized in this study, which spanned nearly a year, is unique, particularly for currents and waves, which were never previously available in this area. The results illustrated that the water level exhibited a spatial and temporal variation ranging from hourly to seasonal oscillation. However, the hourly water level highest annual range recording during the study period at St1 (Umm Qasar port) and St2 (Khor Al-Zubair port) was about 4.77 and 5.88 m, respectively. Correspondingly, the results showed that the current speed is high at both flood and ebb tides, exceeding 1 m/sec, and in general, the ebb currents are stronger than the flood currents. The highest current measured was 1.83 m/sec. Moreover, the results revealed that the highest and lowest wave height (Hs) recordings in the Khor Al-Zubair channel (KAZC) reached 0.22 and 0.03 m, respectively. Correspondingly, our results demonstrated that the wave period’s maximum, minimum, and average were 5.51, 3.96, and 4.5 sec, respectively.

Taxonomic revision of genus Loxoconcha in Japan and Vietnam and its origin

Doan Dung Le — 2025-03-31

In preceding the study, 30 species of the genus Loxoconcha, which were collected on reef slopes, reef flats, tidal beaches, and river mouths in Japan and Vietnam from 2012 to 2015, are reviewed taxonomically. Based on carapace characteristics, such as hinge, fulcral point, muscle scars, and frontal scars, the results show that 27 species still prove to be the genus Loxoconcha. However, two species are assigned to Bonnyannella and one to Sagmatocythere and re-described. In addition, this research also initially reveals the origin and distribution in the Atlantic Ocean of the genus Loxoconcha which is considered as one of the most diversified recent genera in marine ostracods. Fossil records of Loxoconcha species worldwide show that the origination of the genus Loxoconcha may be in Indo-West Pacific Region and by the Late Oligocene (possibly the Late Eocene). To this day, most fossil records of the genus Loxoconcha belong to group A. Among the three subgroups of group A, species subgroup A1 is distributed widely in Indo-West Pacific Region, and therefore, subgroup A1 may be an origin group of the genus Loxoconcha. The geographical distribution of subgroups A2 and A3 mainly restricted within European marine water, including the Mediterranean Sea, meanwhile subgroup A1 lives around the World except for the distributional areas of subgroups A2 and A3, suggesting that the Atlantic Ocean may be a barrier to dispersing subgroups A1 and A2 (and A3).