South Central Vietnam Research Articles

The diversity of commercial marine bivalves in the Nha Phu Lagoon, Khanh Hoa Province, south-central Vietnam

The study was conducted as part of the Joint Vietnam–Russia Tropical Science and Technology Research Center’s project on indicator organisms in the marine environment of south-central Vietnam. The research focused on coastal areas with significant anthropogenic impacts, revealing that biological resources directly affect the livelihood and activities of coastal populations. These resources are dynamic and subject to both human and natural factors. The material from the soft-bottom zone was collected using a grab rake with a mesh bag at the end. Scuba diving equipment was used in areas with a hard substrate and mudflats. In addition, during sample collection, several mollusc specimens were acquired from fishermen who cought marine organisms in that lagoon. Comparing the results with previous studies on bivalve resources in the area, the Nha Phu Lagoon was found to harbour a wide range of economically valuable bivalve species. A total of twenty-seven bivalve species from thirteen families were identified, with the family Veneridae having the highest number of species (eight). The most abundant catches were from the families Ostreidae and Mytilidae, primarily consisting of Magallana gigas (Thunberg 1793) and Perna viridis (Linnaeus 1758), both cultured in the lagoon. Apart from their economic value, these two species also play crucial roles in the ecosystem by filtering water and retaining organic debris in the environment.

Molecular analysis reveals the evolutionary distinctiveness of the Silver-backed Chevrotain within the genus Tragulus

Abstract The Silver-backed Chevrotain (Tragulus versicolor), a mammal endemic to the unique coastal arid ecosystem in south-central Vietnam, is an enigmatic mouse deer with little information available about its ecology and evolutionary history. The recent rediscovery of the species provides a rare opportunity to clarify its taxonomy and phylogenetic relationship within the genus Tragulus. In this study, we sequenced the complete mitochondrial cytochrome b gene for samples of T. versicolor and T. kanchil from Vietnam. Our molecular results show that the species forms a distinct evolutionary lineage sister to all other species in the genus, confirming the earlier hypothesis based on morphological evidence. However, further research is needed to assess the genetic diversity of the species and design appropriate conservation measures. As the species has not been secured over much of its range, it is recommended that the population in Nui Chua National Park, the only one covered by a protected area, be prioritized for conservation actions. Conserving the species in this unique and imperiled ecosystem will also benefits a suite of locally endemic and threatened species of fauna and flora.

Dinoflagellate composition and environmental conditions in the Xuan Dai Bay, South-Central Vietnam

The dinoflagellate community was investigated in association with environmental factors using a data set in April 2021 and April 2022 in Xuan Dai Bay, South-Central Viet Nam. Environmental variables, including physical parameters and dissolved inorganic nutrients, were measured in April 2022. Seventy-three dinoflagellate taxa were identified for Xuan Dai Bay. There was a significant difference in the number and abundance of dinoflagellates between two parts of the bay, the upper and lower bay. The study showed that dinoflagellates favored an area with good water exchange and were less affected by aquaculture activities. Principal component analysis (PCA) was used to explore the relative abundances of different phytoplankton groups, their diversity indices, and environmental variables at the surface and bottom layers of the two parts of the bay. The results showed that dinoflagellates correlated to physical parameters (e.g., PAR, salinity, temperature) at the surface layer and nutrients at the bottom layer. Dinoflagellates and diatoms are mixotrophic and strongly correlated at the bottom layer in Xuan Dai Bay. This strong relationship in the bay was because of the dominance of a heterotrophic genus, Protoperidinium. The present study provided characteristics of the dinoflagellates in Xuan Dai Bay and the possible impacts of environmental parameters on their abundance. The results can be used for further studies and possibly managing of dinoflagellate blooms in coastal waters.

Another new species of Cyrtodactylus (Squamata: Gekkonidae) from Binh Dinh Province, south-central Vietnam

We describe a new species of the Cyrtodactylus irregularis complex based on six adult specimens from Phu Cat District, Binh Dinh Province, Vietnam. Cyrtodactylus binhdinhensis sp. nov. is morphologically distinguished from the remaining congeners of the C. irregularis group by a combination of the following characteristics: Size medium (SVL up to 80.4 mm); nasal scales 4; internasal single; ventral scales in 39–42 longitudinal rows at midbody; ventrolateral folds present or absent without interspersed tubercles; precloacal pores 6 or 7 in males; 5 or 6 enlarged femoral scales on each thigh; femoral pores 10 in males; postcloacal tubercles 2–4; lamellae under toe IV 18–21; dorsal pattern consisting of slightly clear transverse banding formed by shaped dark brown bands, a continuous neckband with U-shape or triangle shape in the middle, dorsal head surface with small dark brown blotches; subcaudal scales transversely enlarged. In the phylogenetic analyses, the new species is recovered as a sister taxon to C. badenensis with approximately 15.34–16.15% genetic divergence between the two species based on a fragment of the COI gene.

Use of antimicrobials and other medical products in an ethnic minority context of South-Central Vietnam: A qualitative study of vulnerability.

Despite the global threat of antimicrobial resistance (AMR), evidence on the use and quality of medicines at community level is limited, particularly in impoverished, rural areas where prevalence of (bacterial) infections is high. To better understand the processes that drive vulnerability to AMR' effects, this study aimed to assess social factors underpinning access to-and use of-medical products and healthcare, among people from the Raglai ethnic minority in Ninh Thuan Province, Vietnam. We conducted ethnographic research in eight villages in 2018-2019, using interviewing and participant observation methods for data collection. Different types of informants (including community members and healthcare providers) were selected using purposive sampling strategies and analysis was retroductive. Our findings show that, despite the existence of a government-funded health insurance scheme, Raglai people's flexible therapeutic itineraries did not systematically start with formal healthcare. Different types of care (private/informal, public, shamanic) were combined in parallel or in alternation, determined by distance to the provider, cost, workload, perceived diagnostic capacity, perceived severity and aetiology of the illness, and trust in the provider. Available medicines were often tablets dispensed in plastic bags containing labelled tablets, unlabelled tablets (in bulk) or tablets ground to powder. Treatment was often considered effective when it relieved symptoms, which led to abandonment of the treatment course. When symptoms did not speedily abate, the illness aetiology would be reinterpreted, and "stronger" medicines would be sought. The precarious socio-economic status of some Raglai drove them in cycles of severe poverty when additional unforeseen factors such as illness, animal disease or loss of crops arose, hampering access to (in)formal healthcare providers and/or appropriate diagnosis and treatment. We conclude that Raglai communities are structurally unable to buffer themselves against the threat and consequences of AMR. Despite this vulnerability, they are among the least targeted by efforts to optimize antibiotic use, which are concentrated in secondary and tertiary healthcare facilities targeted at urban populations.

Notes on the Courtship and Captive Reproduction of the Southern Vietnam Box Turtle, Cuora picturata, at the Turtle Conservation Center in Cuc Phuong National Park, Vietnam.

Endemic to only three known provinces in South Central Vietnam, Cuora picturata have faced extensive collection pressures for the food, medicinal, and pet trades. Further exacerbating their decline is the lack of protected areas where wild populations exist, with only one known population occurring within a protected area. With threats to wild populations persisting, the development of an assurance colony has been prioritized for C. picturata. The Asian Turtle Program of Indo-Myanmar Conservation has been operating the Turtle Conservation Center (TCC) in Cuc Phuong National Park since 1998. From 2020 to 2022, 24 C. picturata were acquired by the TCC from the illegal trade. With no ideal repatriation plan, these animals provided an opportunity for developing a captive assurance colony at the TCC to safeguard the species from extinction. As semi-aquatic species, box turtles in the genus Cuora are a unique group that shows variations in habitat use and behavior between species. Herein, we documented some specific courtship behaviors not yet described for C. picturata, providing insight into the unique reproductive behaviors of this species.

Colletotrichum nanjingense sp. nov. and C. gloeosporioides s.s. Causing Leaf Tip Blight on Jasminum mesnyi in Nanjing, Jiangsu, China.

Jasminum mesnyi Hance is an important medicinal and ornamental plant. This species is native to South Central China and Vietnam and grows primarily in the subtropical biomes. In June 2022, 17 Colletotrichum strains were isolated from leaf tip blight on foliage of J. mesnyi in Nanjing, Jiangsu, China. Based on morphological characteristics and multilocus phylogenetic analyses of six genomic loci (ITS, CAL, ACT, TUB2, CHS-1, and GAPDH), a new species, namely, C. nanjingense, and a known species, namely, C. gloeosporioides s.s., were described and reported. Pathogenicity tests revealed that both species were pathogens causing leaf tip blight on J. mesnyi. The results provided necessary information for disease control and enhanced our understanding of the diversity of Colletotrichum species in China.

Determining Causes of Erosion and Sedimentation at Cua Dai Beach, Quang Nam Province, Vietnam: Applying an Integrated Geographical Approach

Cua Dai is one of the 21 estuaries in the Central region and is the first river mouth to the north of the South Central Coastal region. It is renowned for its beautiful beaches, which attract many tourists. Additionally, the Cua Dai River mouth area is a fishing ground for local fishermen due to its rich marine biodiversity. However, a serious issue has emerged in this area. Cua Dai Beach has been facing severe erosion for several years, threatening its natural beauty. This article employs an integrated geographical approach, utilizing two main methods: document collection (research on geology and hydrodynamics) to determine historical changes and on-site surveys (in point format) to assess the extent and current status of erosion. Information exchange with residents is also conducted to understand the situation and gather data identifying the causes of erosion and sedimentation in the Cua Dai area, part of the lower Thu Bon River system in south-central Vietnam. The results indicate that erosion and sedimentation in the research area are influenced by both natural and anthropogenic factors, with no single factor prevailing.

Impact Assessment of Land Use and Land Cover Change on the Runoff Changes on the Historical Flood Events in the Laigiang River Basin of the South Central Coast Vietnam

Impact Assessment of Land Use and Land Cover Change on the Runoff Changes on the Historical Flood Events in the Laigiang River Basin of the South Central Coast Vietnam

Smallholder farmers’ perception and adoption of digital agricultural technologies: An empirical evidence from Vietnam

This study examines smallholder farmers’ perception of digital agricultural technology and factors that shape the smallholders’ adoption of it in South Central Vietnam. A sample size of 202 smallholder farmers was randomly chosen from a total population of 407 smallholder farmers. Descriptive statistics and a binary logistic regression were used to analyse the data. The results show that the internet and connectivity/wireless, mobile applications and digital platforms are the common digital technologies used by smallholder farmers and these are also the most effective digital technologies for dealing with agricultural production and marketing issues. It can be concluded that younger smallholder farmers who had higher education levels, who interacted with scientists and possessed large farms are in a better position to adopt digital technologies of the internet and connectivity/wireless, mobile applications and digital platforms than older smallholder farmers who had lower education levels, did not interact with scientists and owned small farms. Smallholder farmers who participated in training programs, was member of community-based organisations and contacted with extension workers tend to be digital technology users of the internet and connectivity/wireless and mobile applications. Smallholder farmers who live far from local markets tend to be digital technology users of digital platforms compared to those who live close to one. The provision of training courses on the use of digital technologies in agriculture that consider demographic, socio-economic and institutional characteristics of smallholders when designing and delivering, is a proper agricultural extension strategy which can foster the smallholder farmers to adopt digital technologies for managing agricultural production and marketing systems.

Assessing Social Vulnerability to Climate Change in a Fishery-Dependent Village in South Central Vietnam

Fishery-dependent communities are highly susceptible to the impacts of climate change due to their proximity to vulnerable coastal areas and reliance on ecosystem services for their livelihoods. The study assessed the effects of climate change on the socioeconomic livelihoods and adaptive capacity of Xuan Tu, a community located in South Central Vietnam. The assessment employed the social vulnerability index (SVI) and adaptive capacity index (ACI). A hybrid data collection approach was utilized to gather information from households, and a composite method was employed to aggregate the data, enabling an assessment of community vulnerability. The findings indicated exposure, sensitivity, and adaptive capacity index values of 0.16, 0.34, and 0.26, respectively. The community exhibited a moderate vulnerability to climate change, with a social vulnerability index of 0.43. Notably, economic sufficiency, access to social groups, and level of education emerged as significant factors in reducing social vulnerability. To adapt to climate change, the community modified their fish feeding practices, fish culture methods, increased technology usage, and diversified their sources of income. However, the study identified a lack of institutional support as a significant obstacle to the community's autonomous adaptation. Based on these results, the study recommends livelihood diversification and the implementation of planned adaptation strategies to enhance preparedness for climate emergencies in South Central Vietnam.

Copepod vertical diel migration on the continental shelf of South Central Vietnam

Zooplankton often migrates within the water column for different purposes but mostly to find food and avoid predators. Vertical migration over 24 hours is called diel vertical migration (DVM). However, knowledge of DVM for different zooplankton species is limited. The present study analysized DVM based on species distribution in the water column at each different times of day at two stations on the central Vietnam shelf. One station was on the shelf (LT2) and another was on the shelf slope (FK002). The results showed that 69 zooplankton species, out of 191 recorded at the two stations, having strong DVM (dz > 15 m). Among them, 38 species were nocturnal and 36 species showed reverse DVM. Species with nocturnal DVM were less on the shelf station than on the shelf slope. Moreover, detailed analysis at LT2 showed 18 species having DVM at dawn and 13 species having DVM at sunrise. This study provides important data for zooplankton ecology in Vietnam and marine tropical waters.

Community-Based Pathogen-Specific Incidence of Influenza-Like Illness Due to Respiratory Viruses in South-Central Vietnam in 2009–2012, after a Pandemic of Influenza A Viruses

Community-Based Pathogen-Specific Incidence of Influenza-Like Illness Due to Respiratory Viruses in South-Central Vietnam in 2009–2012, after a Pandemic of Influenza A Viruses

THE DIVERSITY OF CERCARIAE FROM FRESHWATER SNAILS IN LOWLAND AREAS OF BINH DINH AND PHU YEN PROVINCES, VIETNAM.

A survey was conducted in the lowland areas of Binh Dinh and Phu Yen provinces in south central Vietnam to study the diversity of digenean cercariae within freshwater snails. These regions are known as highly endemic areas for the transmission of liver flukes, Fasciola spp. and Opisthorchis viverrini. In total, 13 snail species were found, and 3 of these were dominant, comprising 51.9% of all collected snails, i.e., Bithynia funiculata, Melanoides tuberculata, and Radix auriculata. Cercariae were found in 5 snail species, and among these, Indoplanorbis exustus had the highest overall prevalence of infection (38.5%). No cercarial infections were found in viviparid and ampullariid snails. Morphological identification resulted in 10 cercariae types that were illustrated and measured. Among them, xiphidiocercariae and echinostomata were the most common, causing 70.55% of all cercariae infections. Bithynia species had the most diverse digenean fauna. Molecular data revealed the presence of cercariae of 13 digenean species, including O. viverrini. The 18S rDNA sequences of echinostomata and xiphidiocercariae type 3, which were shed from different snail hosts, were similar to 2 and 3 digenean species, respectively. In conclusion, our findings highlight the diversity of digenean fauna in Binh Dinh and Phu Yen provinces.

Coral reef collapse in South-Central Vietnam: a consequence of multiple negative effects

Coral reef collapse in South-Central Vietnam: a consequence of multiple negative effects

Phase shift from a stony-coral to a soft-coral community on a coral reef: a case study of an alternative state

ABSTRACT A phase shift from a stony-coral community to an alternative state represented by octocorals and corallimorpharians was recorded on a coral reef at the Hon Noi Islands (offshore area of south-central Vietnam). For a seven-year period, average stony-coral cover decreased from 80% to 4.7%, diversity of reef-building corals decreased from 169 to 17 species, and in the shallow area of a reef (1–4 m depth), the cover of corallimorpharians (mainly Rhodactis indosinensis) and octocorals (mainly Clavularia sp.) increased to 62%. Mass scleractinian mortality could have resulted from an outbreak of crown-of-thorns starfish, Acanthaster sp., which developed in the surrounding area in the last decade. The only significant contributor to stony-coral recovery on the study reef to date was the blue coral, Heliopora coerulea. Given the serious coral decline on the upstream reefs as potential sources for coral recruitment and competitive advantages of corallimorpharians and octocorals over scleractinians, the prospects for rapid scleractinian recovery of the study site are poor.

Assessing the status of the Green Peafowl’s “expected stronghold” in dry forests along the Salawin River, north-west Thailand

Summary The suitable habitats of the Endangered Green Peafowl Pavo muticus have declined by 80% over the past century due to extensive anthropogenic degradation. Currently, only six strongholds remain in mainland South-east Asia. While there are estimates of the species’ presence and status in five of these, the sixth one, defined as an “expected stronghold” located in the suitable dry forest along the Salawin River between Thailand and Myanmar, is not well documented. This study assessed the status of the area as a stronghold for the Green Peafowl’s long-term survival by estimating 1) the population density, 2) the current extension of suitable habitats, and 3) the threats to its survival. The area had an estimated density of 0.27 calling males/km2 (CI = 0.07–1.01) inhabiting 9,154 km2 of a mosaic of forest types, including mixed dry pine, mixed deciduous, and dry dipterocarp forests. Higher estimates were reported in other strongholds, including 0.8 birds/km2 in Bago Yoma (Myanmar), 15.8 birds/km2 in north-east Thailand, 1.13–11.34 birds/km2 in HuaiKhaKhaeng Wildlife Sanctuary (Thailand), 0.15–1.7 birds/km2 in northern Cambodia, and 0.15–4.69 birds/km2 in eastern Cambodia / south-central Vietnam. Hunting, habitat disturbance, and the presence of humans posed the greatest danger to the species across the surveyed area. Our results confirm the potential of the area for the species’ long-term survival. However, this “expected stronghold,” which could sustain a population of over 10 calling males/km2 like other high-quality strongholds, is in dire need of a comprehensive management plan to help reduce anthropogenic pressure. Ultimately, transboundary management between Thailand and Myanmar is crucial for the long-term repopulation of this stronghold.

Uncertainties in Systematics of Flying Squirrels (Pteromyini, Rodentia): Implications from a New Record from Vietnam

Taxonomic status of gliding squirrels belonging to the “northern” form of Petinomys setosus known from N. Burma and Thailand has been controversial. Earlier it was assigned to a distinct genus Olisthomys, however, currently it is synonymized with P. setosus s. str. from Sumatra and Borneo Islands, and Malay Peninsula. A squirrel collected in Song Hinh forest (Phu Yen Province, south central Vietnam) was examined genetically using sequence data on three mitochondrial genes (cytb, 12S, 16S) and one nuclear (IRBP) gene. The molecular results demonstrated that this squirrel is significantly divergent from the other examined specimens of Petinomys and belongs to a separate genetic lineage within the Glaucomyina clade. The obtained phylogenetic pattern supports recognition of Olisthomys as a valid genus; however, to confirm this conclusion a comprehensive taxonomic revision of Petinomys and related genera is required. The reconsideration of taxonomic position of the “northern” P. setosus also raises the question of the conservation status of this taxon.

Geochemical and zircon U-Pb geochronological constraints on late mesozoic Paleo-Pacific subduction-related volcanism in southern Vietnam

Late Mesozoic volcanic rocks comprising mainly basalt and basaltic-andesite to dacite occur in south-central Vietnam (Dalat zone) and to a lesser extent in southwestern Vietnam (Bay Nui area). Mineral and whole-rock chemistry indicate a calc-alkaline affinity for samples in the Dalat zone and a high-K calc-alkaline to shoshonitic affinity for rocks in the Bay Nui area. Mineral characteristics and variation diagrams of selected elements suggest that fractional crystallization dominated during magma differentiation. The Bay Nui volcanic rocks generally are more enriched in potassium and LILEs (large-ion lithophile elements) than volcanic rocks from the Dalat zone, which may indicate a more evolved nature or crustal assimilation. The similar chemical characteristics and eruption/emplacement age range of volcanic and plutonic rocks (ca. 90–110 Ma) of equal silica concentration indicate that the magma feeding the volcanic eruptions had the same source as that of the plutonic rocks. The observed mineral and whole-rock compositions with enrichment in LILEs, depletion in HFSEs (high field strength elements), and noticeably negative Nb, Ta, and Ti anomalies are characteristic for arc signatures. Zircon U-Pb geochronological data for the volcanic rocks indicate an age range of 95–105 Ma for the eruption. These geochemical and geochronological data link this Late Mesozoic volcanism with continental arc magmatism driven by the subduction of the Paleo-Pacific beneath eastern Indochina. Zircon xenocrysts with a likely magmatic origin cluster around 350 Ma and 250 Ma, indicating two earlier magmatic events most likely related to the subduction of the Paleo-Tethys beneath western Indochina and the subsequent Indosinian orogeny.

Environmental Concerns for Sustainable Mariculture in Coastal Waters of South-Central Vietnam

Mariculture provides an increasing seafood supply to a growing population. It also brings unintended consequences for the environment, resources, and sustainable development. In an attempt to evaluate the impacts of intensive mariculture of lobster in cages, the water quality and sediment quality in three South-Central regions of Vietnam, Xuan Dai Bay, Van Phong Bay, and Cam Ranh Bay, were monitored from April 2019 to May 2020. In each bay, two stations in the farming areas were compared to a non-farming reference station. The result showed no significant differences in the water quality parameters among the stations within each bay and between the bays. However, sediment quality noticeably differed between sites within each bay and between the bays. The accumulation of the observed parameters of sediment in farming areas was higher than in non-farming areas. In the Cam Ranh Bay, the concentration of organic carbon, total nitrogen, and total phosphorus in the sediment in farming areas was approximately 1.4 times higher compared to non-farming areas. Similar results were found in Van Phong Bay and Xuan Dai Bay with different magnitudes. Additionally, the difference in the sulfide concentration in the sediment of Van Phong Bay was notable for its better environmental quality than the other two. The findings indicated that mariculture wastes would accumulate in the sediment, and decompose over time, causing sediment degradation, which may affect the benthic biota in coastal waters.