Species diversity of rotifers (rotifera: monogononta) in freshwater psammon with three new records to Vietnam

This study aims to evaluate the diversity of rotifers in psammon in the Central Coast of Vietnam. A total of 64 rotifer species belonging to 17 genera and 14 families were recorded in 10 samples collected at hygropsammon zones of freshwater lakes and ponds in Thua Thien Hue province. Lepadella cristata (Rousselet, 1893), Cephalodella tenuior (Gosse, 1886), and Lindia torulosa Dujardin, 1841 were new record to Vietnam rotifers fauna. Species from the families Lecanidae, Lepadellidae, and Trichocercidae are abundant (containing about 44%, 14%, and 12%, respectively) in the total rotifer species recorded. Psammonxenic species accounted for the largest percentage of the psammic rotifer community with 83%, followed by psammonphiles (11%) and psammonbionts (6%). Our study results enrich the data on the diversity and the ecology of rotifers in Vietnam.

Rainfall in Vietnam

<p>The thesis is a comprehensive analysis of the climate of Vietnam, concentrating on rainfall. Vietnam lies in the tropical northern hemisphere in a region that is influenced by the South Asian, East Asian and Australian monsoons. Rainfall here is associated with several different mechanisms, such as the monsoon, tropical cyclones, topography, and so on. From the initial climatological analysis, monsoon and non-monsoon rainfall is investigated. Non-monsoon rainfall is found to be related to a vortex often found off the coast of Vietnam, a newly-understood extension of the “Borneo vortex”. The thesis begins with a study of the surface climate and the general atmospheric circulation over the Southeast Asian region, which dominates Vietnam’s climate. Trends of surface temperature and rainfall were investigated for a 40 year period (1971-2010), using a newly-extended dataset of 60 stations. Vietnam’s average temperature has increased at a rate of 0.26 ± 0.10°C per decade since the 1970s, approximately twice the rate of global warming over the same period. The increase in temperature is statistically significant in most sub-regions. Trends in rainfall are however mostly insignificant in that period. Temperature and rainfall variability are shown to be linked to ENSO on both a national and sub-regional scale. The rainfall climate of Vietnam has been studied in depth, particularly the characteristics of monsoon rainfall and the variability of the length of wet and dry seasons. That investigation has led to the development of an objective monsoon index, based on regional mean sea level pressure and low level zonal wind. While originally developed to define onset and withdrawal dates for the monsoon in Vietnam and over Southeast Asia, the index is shown to be applicable in all monsoon regions of the globe, the first objective index to have such global utility. The final part of the thesis deals with tropical vortex activity and its associated rainfall. Vortices exist almost year-round, migrating from the coast of Vietnam – Southeast Asian Sea - Philippines in summer to the Borneo Island region in winter. Clear evidence is found for the presence of a semi-permanent vortex near the south coast of Vietnam or the north of the Southeast Asian Sea – Maritime Continent (SEASMC) region. It is this vortex and the tropical cyclones over the SEASMC region that significantly contribute to the Vietnam rainfall, particularly the post-monsoon rainfall in Central Vietnam.</p>

Rainfall in Vietnam

<p>The thesis is a comprehensive analysis of the climate of Vietnam, concentrating on rainfall. Vietnam lies in the tropical northern hemisphere in a region that is influenced by the South Asian, East Asian and Australian monsoons. Rainfall here is associated with several different mechanisms, such as the monsoon, tropical cyclones, topography, and so on. From the initial climatological analysis, monsoon and non-monsoon rainfall is investigated. Non-monsoon rainfall is found to be related to a vortex often found off the coast of Vietnam, a newly-understood extension of the “Borneo vortex”. The thesis begins with a study of the surface climate and the general atmospheric circulation over the Southeast Asian region, which dominates Vietnam’s climate. Trends of surface temperature and rainfall were investigated for a 40 year period (1971-2010), using a newly-extended dataset of 60 stations. Vietnam’s average temperature has increased at a rate of 0.26 ± 0.10°C per decade since the 1970s, approximately twice the rate of global warming over the same period. The increase in temperature is statistically significant in most sub-regions. Trends in rainfall are however mostly insignificant in that period. Temperature and rainfall variability are shown to be linked to ENSO on both a national and sub-regional scale. The rainfall climate of Vietnam has been studied in depth, particularly the characteristics of monsoon rainfall and the variability of the length of wet and dry seasons. That investigation has led to the development of an objective monsoon index, based on regional mean sea level pressure and low level zonal wind. While originally developed to define onset and withdrawal dates for the monsoon in Vietnam and over Southeast Asia, the index is shown to be applicable in all monsoon regions of the globe, the first objective index to have such global utility. The final part of the thesis deals with tropical vortex activity and its associated rainfall. Vortices exist almost year-round, migrating from the coast of Vietnam – Southeast Asian Sea - Philippines in summer to the Borneo Island region in winter. Clear evidence is found for the presence of a semi-permanent vortex near the south coast of Vietnam or the north of the Southeast Asian Sea – Maritime Continent (SEASMC) region. It is this vortex and the tropical cyclones over the SEASMC region that significantly contribute to the Vietnam rainfall, particularly the post-monsoon rainfall in Central Vietnam.</p>

Comparative genomics of Nocardia seriolae reveals recent importation and subsequent widespread dissemination in mariculture farms in South Central Coast, Vietnam

Between 2010 and 2015, nocardiosis outbreaks caused by Nocardia seriolae affected many permit farms throughout Vietnam, causing mass fish mortalities. To understand the biology, origin, and epidemiology of these outbreaks, 20 N. seriolae strains collected from farms in four provinces in the South-Central Coast of Vietnam, along with two Taiwanese strains, were analysed using genetics and genomics. Pulsed-field gel electrophoresis identified a single cluster amongst all Vietnamese strains that was distinct from the Taiwanese strains. Like the PFGE findings, phylogenomic and single-nucleotide polymorphism (SNP) genotyping analyses revealed that all Vietnamese N. seriolae strains belonged to a single, unique clade. Strains fell into two subclades that differed by 103 SNPs, with almost no diversity within clades (0-2 SNPs). There was no association between geographic origin and subclade placement, suggesting frequent N. seriolae transmission between Vietnamese mariculture facilities during the outbreaks. Vietnamese strains shared a common ancestor with strains from Japan and China, with the closest strain, UTF1 from Japan, differing by just 217 SNPs from the Vietnamese ancestral node. Draft Vietnamese genomes range from 7.55-7.96 Mbp in size, have an average G+C content of 68.2%, and encode 7,602-7,958 predicted genes. Several putative virulence factors were identified, including genes associated with host cell adhesion, invasion, intracellular survival, antibiotic and toxic compound resistance, and haemolysin biosynthesis. Our findings provide important new insights into N. seriolae epidemiology and pathogenicity and will aid future vaccine development and disease management strategies, with the ultimate goal of nocardiosis-free aquaculture.

PHYLOGENETIC ANALYSIS AND SPECIES IDENTIFICATION OF 11 GORGONIAN CORALS (OCTOCORALLIA: ALCYONACEA) IN THE NORTH CENTRAL COAST OF VIETNAM BASED ON MSH1MTDNA AND 28S RDNA MARKERS

Vietnam contains diverse marine ecosystems with the high biodiversity of marine organisms, including gorgonian corals of Alcyonacea order. In order to support traditional classification of these corals, in this study mitochondrial barcoding markers msh1 and nuclear 28S rDNA were developed for analysis of 11 specimens collected in 2015 and 2016 from different islands and bays along the North Central coast of Vietnam. Phylogenetic analyses based on msh1 and 28S sequence polymorphism showed that all specimens belonged to Anthozoa class, Octocorallia sub-class and Alcyonacea order. At lower taxa levels, they were divided into 4 sub-orders, 7 families and 7 genera according to 7 distinct clades with bootstrap values from 99-100%.The identifications of 7 out of 11 specimens including Sinularia brassica (2 specimens)and Sinularialeptoclados, Dichotellagemmacea, Annella reticulata, S. conferta and S. nanolobata were in concordance between morphological and molecular methods. The other 4 specimens were only identified at genus levels of Astrogorgia sp., Melithaea sp. Scleronephthya sp. and Muricella sp. by either msh1-morphology or msh1-28S markers. These results highlight the importance of molecular markers to elucidate patterns of biodiversity and species identification of soft coral.

Prospects for development of Vietnam underwater springs

The issues of the relevance of exploration and development of seabed deposits are considered. The article provides information on the history and composition of studies of solid mineral deposits carried out in the South China Sea by scientists of the Democratic Republic of Vietnam. The oceanographic and geological characteristics of the Pacific coast of Vietnam, its shelf and continental slope are given. The conditions that form placer deposits in the exclusive economic zone of Vietnam are given, and their brief description is given. Examples of various placers in the shelf zone, their features are given, and schematic diagrams of occurrence are given. The dependence of the littoral width on the height of the tidal wave and the angle of inclination of the shelf is analyzed. Proposals are given on the possibility of developing alluvial deposits in the littoral zone using dry drilling equipment, the advantages and disadvantages of this technology are stated. The features of the influence of climatic conditions of the Pacific coast of Vietnam on the use of hydromechanized technologies in the development of underwater placers are noted. Emphasis is placed on maintaining the ecological balance in the fields of development and the continuation of further research in the South China Sea.

The Hungry Snail, the Fragile Coral, and the Friendly Microbe

Off the coast of Vietnam, two recent events seem to have contributed to the death of coral reefs: the rapid invasion of a small marine snail called Drupella, and the emergence of a disease that spreads over corals. We decided to investigate whether there is a link between the corals, the snails, and the disease. We analyzed the mucus covering the surface of corals, both in healthy corals and those infested by Drupella snails. Mucus produced by corals is usually full of helpful microbes, protecting the corals from harmful microbes that can make them ill or kill them. Our analyses showed that, when Drupella eats corals, the snail also removes one of the corals’ primary defenses by eliminating most of the tiny protectors in their mucus. This allows harmful microbes to cause additional damage to the corals.

Assessment of Soil Liquefaction Potential Based on SPT Values at Some Ground Profiles in the North Central Coast of Vietnam

The North Central Coast of Vietnam has a wide distribution of loose sand which is often exposed on the surface. The thickness changes from a few meters to over ten meters. This sand with the loose state can be sensitive to the dynamic loads, such as earthquakes, traffic load, or machine foundations. It can be liquefied under these loadings, which might destroy the ground and buildings. The Standard Penetration Test (SPT) is widely used in engineering practice and its values can be useful for the assessment of soil liquefaction potential. Thus, this article presents some ground profiles in some sites in the North Central Coast of Vietnam and determines the liquefaction potential of sand based on SPT and using three parameters, including the Factor of Safety against Liquefaction (FSLIQ), Liquefaction Potential Index (LPI), and Liquefaction Severity Number (LSN). The research results show that the FSLIQ, LPI, and LSN values depend on the depth of sand samples and the SPT values. In this study, the sand distributed from 2.0 to 18.0m with (N1)60cs value of less than 20 has high liquefaction potential with FSLIQ<1, LPI is often higher than 0.73, and LSN is often higher than 10. The results also show that many soil profiles have high liquefaction potential. These results should be considered for construction activities in this area.