Gio Mangrove Biosphere Reserve Research Articles

Antibacterial activity of methanol extract from Wedelia biflora (L.) DC. growing in the Can Gio Mangrove Biosphere Reserve, Vietnam

The study investigated antibacterial activity of methanol extract of Wedelia biflora (L.) DC. (Wollastonia biflora or Melanthera biflora) growing in the Can Gio Mangrove Biosphere Reserve, Vietnam by using agar well diffusion method. Antimicrobial activity strength of Wedelia biflora (L.) DC. was depended on diameter of antibacterial zone causing by the methanol extract. The findings showed that methanol extract of whole plants, Wedelia biflora (L.) DC. exhibited antibacterial activity against Gram (+) bacteria: Bacillus cereus and Staphylococcus aureus but negative effects on Gram (-) bacteria: Pseudomonas aeruginosa and Escherichia coli. Its antibacterial activity increased with increase in extract concentration. Only extract with concentration of 1000 mg mL-1 had moderately antibacterial strength against B. cereus but the extract with other tested concentrations had antibacterial activity at weak level according to Manuanza’s rating scale of antibacterial zones.

Investigation on antibacterial ability of acetone extract from leaves of Avicennia alba Blume growing in the Can Gio Mangrove Biosphere Reserve, Vietnam

Investigation on antibacterial ability of acetone extract from leaves of Avicennia alba Blume growing in the Can Gio Mangrove Biosphere Reserve, Vietnam

Digenean infections in snails (cercariae stage) in Can Gio Mangrove Biosphere Reserve, Ho Chi Minh City, Vietnam

Foodborne zoonotic trematodiasis is a public health problem in many countries. A study on digenean larvae (cercariae stage) obtained from snails in all ten main small canals and two rice fields was carried out in Can Gio Mangrove Biosphere Reserve, Ho Chi Minh city, Vietnam to identify the snail composition and digenean prevalence in snails. The snails were sampled in the dry season (January 2022) and the wet season (June 2022). In the ten canals, 23 snail species belonging to 16 genera, 10 families from the samplings were found; however, there were no cercariae in these 23 snail species. In the two rice fields, 11 snail species in 11 genera and 7 families were collected. In which, Bithynia siamensis in Ly Nhon rice field and Thiara scabra in Binh Khanh rice field infected xiphidio cercariae. For Bithynia siamensis, the prevalence in the dry season (5.6%) was higher than in the wet season (4.6%) (P > 0.05). In Binh Khanh rice field, only one Thiara scabra infected cercariae in the wet season. Further research on digenean infection in different months and in other water bodies in Can Gio Mangrove Biosphere Reserve should be done to contribute to the control of digeneans and reserve the biodiversity.

Variation in sediment characteristics between canopy gap and surrounding forest in Can Gio Mangrove Biosphere Reserve, Vietnam

This study presented the difference in the sediments under a large gap formed by the Durian typhoon in 2006 and its surrounding intact forest in Can Gio Mangrove Biosphere Reserve, Vietnam. Twelve plots previously settled in the original gap and its surrounding forest were used to collect sediments in the dry and wet season in 2019 to assess the difference in sediment properties and nutritional state caused by the self-recovery of the vegetation. Sediment temperature and pH were measured in field, while the contents of total organic carbon (Corg) and total nitrogen (Ntot) were subsequently quantified in the chemical laboratory. Sediment temperature, salinity, and pH between the gap and the surrounding forest were not statistically different. The variation of Corg concentration in the gap sediments seemingly increased with depth from 1–15 cm in the dry season. The Ntot in the gap sediments showed that it was continuously consumed in the underlying sediments during both seasons. In conclusion, the variation in vegetation composition between the gap and its surrounding forest was responsible for the differences in sediment C and N concentrations.

Identification of Non-Impact Livelihoods on Mangrove Resources in Can Gio, Vietnam

There are several negative impacts on mangrove resources related to 11 existing livelihoods in Can Gio district, where socio-economic development has created many changes in livelihood conditions and ecological environment of the mangrove forests [1]. As a result, the study focuses on identifying and selecting livelihood types that have no impacts on mangrove resources based on primary data collected from 537 structured questionnaires and 45 in-depth interviews with experts, forest keepers and local households about understanding of the activities of 11 current livelihoods and environmental conditions of the study areas in the past 10 years.Qualitative data analysis, non-impact livelihood scale and AHP analysis allow the analysis and identification of 6 livelihood types appropriate for the goal of avoiding mangrove resource degradation to conserve, maintain, and sustainably develop mangrove ecosystems for Can Gio Mangrove Biosphere Reserve.

CO<sub>2</sub> Exchange Of Seedlings Of <i>Rhizophora Apiculata Bl.</i> In Artificial And Natural Mangrove Forests Of Southern Vietnam

Mangrove forests are an important part of tropical coastal ecosystems. Until recently, these forests were intensively exterminated. Currently, the issue of mangrove conservation is being discussed at a number of symposiums due to their significant role in reducing the effects of greenhouse gas emissions. However, there has recently been uncertainty in estimation of CO2 fluxes in mangrove forests due to a lack of field research. The results of studies of photosynthesis at the leaf level in-situ in seedlings of Rhizophora apiculata Blume, 1827 of both natural and artificial origin are presented. The studies were carried out on a mangrove plantation growing in Can Gio Mangrove Biosphere Reserve, which is 50 kilometres from Ho Chi Minh City (South Vietnam). CO2 gas exchange during photosynthesis was measured using a gas analysing system called the LI-6800 (USA). Photosynthetically active radiation (PAR) is the main factor affecting the photosynthesis of the studied seedlings. Artificial seedlings that were grown in open areas had higher productivity and greater photosynthetic rates. It has been determined that the measured photosynthesis are scattered over three clearly marked zones, which correspond to the measurements of photosynthesis made in the pre-noon, noon and afternoon hours. The water reserves used up before noon were not fully replenished in the afternoon by the seedlings. Based on the results obtained, it has been suggested that the main inhibitory factor affecting the photosynthesis of R. apiculata (if PAR is not taken into account) is a violation of the water balance of the leaves.The optimum air temperature for photosynthesis processes in seedlings is (35 ± 2) °C. The intensity of photosynthesis also increases with an increase in the concentration of CO2 in the air. The increases of photosynthesis continue until the concentration of CO2 reaches ~1000 µmol·mol-1 and then do not increase. We associate this circumstance with the maximum possibilities of the photosynthetic apparatus of the leaf of the studied plant. The obtained research results will contribute to a better theoretical understanding of the productivity of plants of this species in the respective ecosystems, and will also allow us to move from photosynthesis at the leaf level to photosynthesis at the planting level. The work’s mathematical models can be used to model changes in R. apiculata photosynthesis from the point of view of climate change.

Evaluation of the carbon storage in the sediments in the mangrove ecosystem growing on abandoned salt pan in Can Gio District, Ho Chi Minh City, Vietnam

This study aims to evaluate the size of the sedimentary carbon sink in the coupling with environmental conditions in a mangrove planted in an abandoned salt pan in Can Gio Mangrove Biosphere Reserve. Sediment samples were collected at four sites chosen based on their dominant plant species. Sediment temperature, pH, salinity, humidity and wet bulk density were measured in field, while the nutrients (NH4+, PO43-) and organic carbon (Corg) concentrations were determined in the laboratory. The results showed that humidity, salinity and bulk density were strongly correlated with Corg concentrations. The amounts of organic carbon stored in the sediments in the dry and wet season were 380 MgC.ha-1 and 552 MgC.ha-1 respectively. Sediment humidity and salinity were the primary factors governing the size of the sedimentary carbon sink. The concentrations of organic carbon and ammonium were influenced by an allochthonous source entering the study area via the tidal creek network.

Antibacterial activity of ethanol extract and decoction from Avicennia alba Blume growing in the Can Gio Mangrove Biosphere Reserve, Vietnam

This study was conducted to find out the antibacterial ability of a folk medicinal plant in Can Gio Mangrove Biosphere Reserve, Avicennia alba Blume. Leaf powder of A. alba derived from 3 different locations in the Biosphere Reserve was used to make ethanol extracts and decoctions. Methods to evaluate antibacterial ability included agar well diffusion, and Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). The results showed that the ethanol extract from Dan Xay site was resistant to 6 tested bacterial strains including Bacillus cereus, Bacillus subtilis, Staphylococcus aureus, Enterococcus faecium, Pseudomonas aeruginosa, Escherichia coli. Most of the decoction samples had bacteriostatic and bactericidal properties with MBC/MIC rates ranging from 1.43 to 10.0.

Antibacterial activity of ethanol extract and decoction from Avicennia alba Blume growing in the Can Gio Mangrove Biosphere Reserve, Vietnam

Antibacterial activity of ethanol extract and decoction from Avicennia alba Blume growing in the Can Gio Mangrove Biosphere Reserve, Vietnam

Monitoring landscape fragmentation and aboveground biomass estimation in Can Gio Mangrove Biosphere Reserve over the past 20 years

Over the past 20 years, the mangrove landscape of Can Gio Mangrove Biosphere Reserve (MBR) has undergone drastic changes in space and time. However, we know very little about changes in mangrove landscape model characteristics from analysis of different aspects based on landscape fragmentation. In the present study, the temporal and spatial changes of landscape pattern of land use/land cover (LULC) over the past 20 years in Can Gio Mangrove Biosphere Reserve (MBR), southern Vietnam were analyzed based on remote sensing data, with high classification accuracy (overall accuracy >85%, Kappa >0.8). The present study selected representative landscape indexes and built an integrated landscape index to examine the spatial-temporal changes of landscape patterns. Overall, over the past 20 years, the degree of fragmentation has gradually increased, mainly occurring in the transition zone of MBR. These changes are intended to reflect the significant temporal variation of the MBR, where the ecosystem is strongly disturbed by the intensity of human activities. We then investigate the effectiveness of principal component analysis (PCA)-based machine learning techniques in estimating the mangrove AGB, and applying landscape indices to assess impacts in Can Gio MBR. It reveals that the ANN model obtained the highest prediction accuracy (R2train = 0.785), followed by GPR (R2train = 0.703), and SVM (R2train = 0.671). As a result of applying the ANN model, the predicted mangrove AGB in 2000 and 2020 in the study site ranged from 6.531 to 368.163 Mg ha−1, and 13.749 to 320.295 Mg ha−1, respectively. These results support the application of the model as a tool to support LULC management and protection in the study site, and to contribute insights into the future mangrove research in other regions of the world.

Assessment of livelihood risks due to climate change and ecological resources in Can Gio mangrove biosphere reserve, Vietnam

Can Gio Mangrove Biosphere Reserve was recognized as a global biosphere reserve by UNESCO in 2000 with a typical diverse flora and fauna of the mangroves of Vietnam and Southeast Asia. People’s livelihoods in Can Gio depend largely on natural resources. Thus, any negative changes due to climate change will directly affect their livelihoods. These changes are potential risks affecting the livelihoods of local residents.The study was conducted based on the interview results of 537 local residents using a structured questionnaire and 45 in-depth interviews using data of open-ended questions designed based on the 5-point Likert scale. A set of criteria was developed according to the sustainable livelihood framework of DFID (1999) and climate change framework of IPCC (2014) to assess the impacts of environment and climate change on livelihood risks in the study area.This study used weighting methodology for qualitative data and GIS methodology to identify the risks of 13 livelihood genres affected by changes in climate and ecological resources of Can Gio mangrove forest. The results show that there is a difference in the levels of livelihood risk caused by climate change. Almost thirteen types of livelihoods have high risks caused by climate change. As a result, there should be a risk management strategy which focuses on solutions to control hazards, exposures and vulnerabilities, along with measures to protect and support livelihood resources for Can Gio local residents.

Investigating the Correlation of Microplastic Pollution Between Seawater and Marine Salt Using Micro-Raman Spectroscopy

Microplastics (MPs) are synthetic polymer pieces with a size of less than 5 mm that are ubiquitous in the marine environment. They have been recently detected in several wild species and sea products. An indispensable condiment in human food is marine salt that is produced from seawater. Since toxicity studies report potential health impacts when plastic debris is ingested, more attention must be paid to the MP contamination of sea salt and the underlying reasons for this. The central aim of this study is to evaluate the MPs contamination level of sea salt in correlation with the MPs contamination level of seawater in Vietnamese areas. Micro-Raman spectroscopy was employed to determine MPs in the samples collected from three artificial salt pans of Vietnam. The result revealed the presence of MPs in all study areas—Vung Tau (VT;14.54 MPs/L seawater and 114.67 MPs/kg salt), Ly Nhon (LN; 13.14 MPs/L seawater and 63.59 MPs/kg salt), and Can Thanh (9.42 MPs/L seawater and 93.69 MPs/kg salt). The comparisons highlight close correlations in the percentage, shape, size, and color of MPs, especially polyethylene, polyethylene terephthalate, and polypropylene particles extracted from the seawater and its salt. This study proved that seawater is a plastic pollution source for salts produced by traditional seawater evaporation. The study also alerts the prevalence of MPs in the environment and human consumables, thereby indicating that actions must be taken to reduce the pollution of water sources in Vung Tau and at the UNESCO Can Gio Mangrove Biosphere Reserve and improve salt production and refinery processes in order to minimize the number of MPs in final salt products for safe consumption.

Comparison of Microplastic Pollution in Beach Sediment and Seawater at UNESCO Can Gio Mangrove Biosphere Reserve.

Microplastics have become a global concern due to their persistent properties and impacts on the marine environment. This research investigates pollution sources and behaviors of microplastics at UNESCO Can Gio Mangrove Biosphere Reserve. Density flotation with sodium chloride is employed to extract microplastics from sand at Can Gio Beach, and a double‐filtration procedure is developed to recover microplastics from seawater at the beach and Dong Tranh Cape. The microplastics’ morphology and type are analyzed by micro‐Raman spectroscopy. The results show that microplastics are accumulated at concentrations from 31.99 to 92.56 MPs g−1 at various sand layers. The seawater at Can Gio Beach and Dong Tranh Cape contains 6.44 and 3.75 MPs L−1 of microplastics, respectively. White polyethylene fragments predominate, and all the microplastics comprise small secondary microplastics with a minimum size of 25 µm and a maximum size of 260 µm for fragments and a length of 640 µm for fibers. The proportions of polyethylene, polypropylene, polystyrene, and polymethylmethacrylate are similar. The differing percentages of other compositions in sand and seawater are attributed to the morphology and density of the microplastics. The results indicate the extent of microplastic pollution and suggest appropriate strategies for tourism development at the Biosphere Reserve.

Green GRDP calculation by total economic value methods: Case study in Cần Giờ mangrove biosphere reserve

In the context that Vietnam develops for international integration, the government has oriented socio-economic development to develop in a sustainable way, not kind of development at all costs. This is clearly shown through the fact that ministries and governmental institutions have adjusted policies and target programs to achieve the millennium goal set by the United Nations to serve the action plan for the sustainable development of the entire nation. From the point of view of sustainable development, many countries around the world have calculated green GDP instead of normal GDP to see that economic development must be closely linked to social progress and environmental protection. Throughout many years of research on the total economic value of a system of environmental resources, especially the total economic value of the humanistic ecology system of Can Gio Mangrove Biosphere Reserve, the author found that there are similarities in the calculation of green GRDP and that of the total economic value of a geographic area. This paper aims to present a conceptual framework to calculate the green GRDP for the Can Gio Mangrove Biosphere Reserve, using total economic value methods. The author also links the United Nations documents and the Statistics Law with the Government of Vietnam's guiding documents for implementing the law to formulate a green GRDP calculation conceptual framework using the methods of total economic value calculation. To calculate the Green GRDP of Can Gio Mangrove Biosphere Reserve by using the total economic value methods is an illustration to convince the validity of the Green GRDP Conceptual Framework. Hopefully there will be many comments from scientists and managers to be able to unify how to calculate green GRDP for mangrove areas and to move towards calculating green GRDP for the national economy, in order to manage the balance between "conservation for development" and "development for conservation" according to the trend of sustainable development.

Factors governing phytoplankton community in the Can Gio mangrove biosphere reserve, Vietnam

This paper covers spatial and temporal variations in phytoplankton communities and physico-chemical water properties in the Can Gio Mangrove Biosphere Reserve (CGMBR), Vietnam based on field measurement conducted in dry and wet seasons of 2010. Phytoplankton samples and water parameter data were collected from nine stations in the CGMBR. A total of 86 species were recorded with clear dominance of Bacillariophyceae, which formed above 90% of the total phytoplankton abundance with average of 48,000 cell/l in dry season and 35,000 cell/l in wet season. Although Chaetoceros and Coscinodiscus were the two most diverse genera, Skeletonema showed high abundance during the studied period. Among the ten environmental parameters tested in this study, salinity, turbidity, nitrate, ammonium and silicon dioxide were found to be significantly different between seasons. On the other hand, no significant difference was found between stations for the studied physico-chemical parameters. Results of CCA indicated that the phytoplankton assemblage in CGMBR was influenced by salinity, turbidity, nitrate, ammonium and phosphate concentration. This is the first study simultaneously investigating the phytoplankton communities and their environment in this area and it is essential to set up the baseline of future studies.

Trophic relationships and basal resource utilisation in the Can Gio Mangrove Biosphere Reserve (Southern Vietnam)

Fatty acid biomarkers and dual stable isotopes (δ13C and δ15N) were used to identify the preferred food sources of consumers in a mangrove tidal creek and nearby unforested (mud bank) and forested areas located in the Can Gio Mangrove Biosphere Reserve (Southern Vietnam). We analysed 15 macro-invertebrates and 1 fish species representing primary consumers and their immediate predators in this area. Specific groups of fatty acids were used to trace the fate of various food sources (i.e., suspended particulate organic matter, mangrove litter and sedimentary organic matter). The δ13C and δ15N of consumers ranged from −26.9 to −18.8‰ and from 1.1 to 9.9‰, respectively. The trophic pathway based on mangrove litter, characteristic of mangrove ecosystems, is nutritionally sustaining various crab and snail species. In contrast, it appears that the most mobile species (fish and shrimps), living in the water column and possibly migrating with tides, are mostly feeding on suspended particulate organic matter, suggesting that this trophic pathway is of great importance for connectivity among tropical coastal ecosystems. Our study suggests that snails and crabs mainly act as mineralisers, processing high quantities of detrital material to meet their nutritional needs and thus releasing nutrients through the production of faeces, that are further mineralised by microorganisms, while locally grown phytoplankton reintegrates these compounds into its biomass and feeds migrating species. We highlight here a possible link between mangrove litter and coastal food webs.

Erosion and deposition processes from field experiments of hydrodynamics in the coastal mangrove area of Can Gio, Vietnam

Summary Studying hydrodynamic processes is necessary for understanding the sediment erosion–deposition mechanism in mangrove areas. The hydrodynamic effects within the mangrove area of the Dong Tranh Estuary in the Can Gio Mangrove Biosphere Reserve in Ho Chi Minh City (HCMC), Vietnam are very complicated and are caused by the mixed impacts of waves, tides, currents and suspended sediment concentrations (SSCs). In this study, the measurements of hydrodynamics such as waves, currents and SSCs were conducted in the dry (Feb. 2012) and wet (Jun. 2014) seasons. Three stations were set up within the estuary, mud-flat and mangrove forest. The analysed results showed that the hydrodynamics in all three stations were strongly influenced during the first dry monsoon season and the next wet one. The waves were the main factor during the dry season and contributed more SSC turbulence in the mud-flat, potentially causing erosion at the study site. Meanwhile, the current velocities in both the estuary and mud-flat sites were major factors during the wet season. In the mangrove forest, the SSC during the dry season changed due to the tidal cycle. Additionally, two measurements for the change in the topographies and shorelines were conducted from 2014 to 2017. The results show that the study site has been eroding rapidly (0.61 m month−1). Although this study shows a soil retention role for the mangrove forests, the wave energy dissipation occurs mainly within the mud-flat due to the bottom topography. The study site is proven to be eroding.

Nutritional composition of suspended particulate matter in a tropical mangrove creek during a tidal cycle (Can Gio, Vietnam)

Mangrove forests are highly productive ecosystems and mangrove-derived organic matter has generally been assumed to play a basal role in sustaining coastal food webs. However, the mechanisms of mangrove-derived organic matter utilisation by consumers are not fully understood. In this study, we were interested in hourly changes in the nutritional quality of suspended particulate matter (SPM) entering and departing a mangrove creek during a tidal cycle. We determined the fatty acid composition and δ13C stable isotope signature of SPM during a 26 h tidal cycle in a creek of the Can Gio Mangrove Biosphere Reserve (Southern Vietnam). Regarding fatty acids, the nutritional quality of SPM was low during most of the tidal cycle. However, it greatly increased during the first part of the strongest flood tide, occurring during daytime. The pulse of highly nutritive organic matter brought to the ecosystem was mostly composed of algal cells growing in specific shallow zones of the mangrove, that use nutrients and CO2 exported during the preceding ebb tide and originating from the mineralisation of mangrove-derived organic matter, as evidenced by their δ13C signatures. This study confirms that mangrove-derived carbon plays a basal role in sustaining trophic webs of mangrove tidal creeks, but that its nutritive value is greatly enhanced when a first step of mineralisation is achieved and CO2 is photosynthesised by algal cells.

The mangrove's contribution to people: Interdisciplinary pilot study of the Can Gio Mangrove Biosphere Reserve in Viet Nam

The main objective of this pilot study, conducted in June 2015 in the Can Gio Mangrove Biosphere Reserve (Can Gio MBR, Viet Nam), was to develop an interdisciplinary approach to assess some key services provided by reforested mangroves subject to external pressures and varying management policies. We focused on the abundance of viruses, bacteria, endo- and epi- and macrofauna and the diversity of crabs in the mangrove and the exploitation of its resources. The main social finding was that the local inhabitants are aware of the levels of protection of the different zones within the Can Gio MBR and respect them. The core and the buffer zones seem to present a similar ecological status. Genotyping showed a low level of crab diversity although there were many different morphotypes. In the future, we need to understand the stakeholders’ general perception of the biodiversity and environment changes by developing an integrated, multi-scale approach.

Environmental gradients regulate the spatio-temporal variability of phytoplankton assemblages in the Can Gio Mangrove Biosphere Reserve, Vietnam

This paper covers spatial and temporal variation in phytoplankton communities and physico-chemical variables in the Can Gio Mangrove Biosphere Reserve (CGMBR), Vietnam, based on field measurement conducted monthly at nine stations during February 2009 to January 2010. Species diversity, richness and phytoplankton abundance were calculated. Canonical Correspondence Analysis (CCA) was used to investigate the relationship between environmental factors and phytoplankton community. A total of 126 species were recorded with a clear dominance of Bacillariophyceae, which formed about 76.4% of the total phytoplankton counts with an annual average of 44.900 cells/L. Other algal classes like Dinophyceae, Cyanophyceae and Chrysophyceae sustained low counts, forming collectively about 14% of the total abundance of phytoplankton. Although Chaetoceros and Coscinodiscus were the most dominant genera, Schroederella and Skeletonema showed high abundance during the studied period. Among the nine environmental parameters tested in this study, salinity, nitrate and ammonium were found to be significantly different between two seasons. On the other hand, no significant difference was found between stations for the studied variables. Results of CCA indicated that phytoplankton assemblage in the CGMBR was influenced by salinity, nitrate and phosphate concentration. This is the first study simultaneously investigating the phytoplankton communities and their environment in this area and it is essential in order to set up the baseline of future studies.