Search Results (33)

Here, we discuss the results of an experiment in toe-line protection of estuarine embankments from frequent slope failure using silt traps. We test the feasibility of terracotta rings to trap silt and promote natural mangrove regeneration in barren patches in front of embankments around human settlements in the Indian Sundarban region, designated as the Sundarban Biosphere Reserve. The initial results of the first sixteen months of observations, between May 2023 and August 2024, are encouraging. Sediment accumulation in the silt traps across sites ranges between 4 and 42 cm. Periodic granulometric analyses of sediments indicate that while the middle estuarine sites accumulate more clay/silt, the lower estuarine sites accumulate more sand. During the late and post-monsoon seasons, all sites except one, on the eastern coast of the lower estuarine island, exhibit natural mangrove regeneration, the main species being Porteresia coarctata, Sueda maritima and Avicennia marina. Additionally, oysters Saccostrea cuculata and occasionally Crassostrea cuttakensis are found attached to the terracotta silt traps. The results highlight the potential of the nature-based Living Shoreline strategy to support mangrove regeneration and toe-line protection cost-effectively. The study also successfully opens up new possibilities for sustainable elevation management in the sinking and shrinking mangrove region of the Sundarbans, a significant development in the face of climate change and accelerated sea level rise. Full article

This Study delves on changes in the extent of mangroves over a 42 years span in the Douala-Edea NP, Cameroon. Mangroves are valuable ecosystems that provide significant biological, environmental, ecological, and cultural functions. To inform the development of management plans for the ecosystem’s sustainability, it is crucial to evaluate how their land cover, levels of degradation, and phases of restitution have changed. GIS and remote sensing techniques were used to classify and analyze Landsat images from 1980 to 2022 categorized into nine classes: bare ground, Nypa palms, settlements, coastal sedimentation, river sedimentation, regeneration, matured mangroves, dense forest, and water body. Using the Markovian chain approach, the changes noted during the period were utilized to forecast future trends up to 2052. Findings demonstrated that the mature mangrove area decreased throughout the study. The surface area covered by mature mangroves was 80,628.78 hectares in 1980, which decreased by 7.31%, 1.51%, 3.70%, and by 17% for the overall period of 42 years. Additionally, a gain of 6.84% from 1980 to 2022 was observed, probably from artificial mangrove regeneration. Settlements, invasive Nypa palms, bare ground (resulting from over-exploitation), and the sedimentation of rivers and coast primarily replaced mangroves. The prediction derived indicated the continuous decline in mangroves if not fully protected by law. The gazettement to National Park and recent promulgation of two laws are steps in providing the needed protection. These results provide vital information to direct future mangrove conservation actions in the recently gazetted Douala-Edea National Terrestrial and Marine Park and other mangrove blocks along the Gulf of Guinea. Full article

(1) Background: Mangroves are critical ecosystems that provide essential services, including coastal protection, biodiversity support, and carbon storage. However, urbanization and infrastructure development increasingly threaten their sustainability. This study investigates the spatio-temporal trends of mangrove canopy cover in Benoa Bay, Bali, Indonesia, which is an urban area and a center of tourism activities with various supporting facilities. The analysis was conducted from 2013 to 2023, using Landsat 8 satellite imagery and Normalized Difference Vegetation Index (NDVI) analysis. In addition, the analysis was also linked to mangrove area management policies. (2) Methods: The annual NDVI time series based on Landsat 8 imagery, obtained through the Google Earth Engine (GEE), was used to characterize the vegetation canopy cover in the study area. Statistical analysis of the annual linear trend of the NDVI was conducted to examine the spatio-temporal variation in canopy cover. Additionally, policies related to regional spatial planning and area protection were analyzed to assess their role in preserving mangrove forests in urban areas. (3) Results: There was a net decrease in mangrove area in Benoa Bay of 3.97 hectares, mainly due to infrastructure development and tourism facilities. The NDVI trend shows an overall increase in canopy cover due to reforestation and natural regeneration efforts, although there was a local decrease in some areas. Conservation policies, such as the establishment of the Ngurah Rai Forest Park, have supported mangrove protection. (4) Conclusions: The analysis demonstrated that mangroves surrounded by urban areas and tourism activity centers can still be maintained quite well with the right policies. Full article

Although successful in protecting planted mangrove plants, the effectiveness of emergent detached offshore structures in increasing vegetation cover has yet to be definitively determined. We selected Tien Giang Province, Vietnam as an appropriate case study to address this question. We analyzed multiyear (2000 and 2022) shoreline changes and calculated the enhanced vegetation index (EVI) together with ground truthing in pursuit of the objectives of the study. Our findings suggest that emergent detached offshore structures have yet to lead to an increase in vegetation cover or promote mangrove growth. The vegetation growth steadily increased, as did the high level of natural mangrove growth with fully grown mangrove trees, even before the structures were constructed. By 2015, all the categories increased slightly except for low vegetation cover (LVC) and medium vegetation cover (MVC). LVC decreased from 390 ha in 2010 to 291 ha in 2015, while MVC decreased from 305 ha in 2010 to 275 ha in 2015. By 2020, all the categories decreased slightly except for non-vegetation cover—Barren lands (NVC2) and MVC. NVC2 decreased slightly from 404 ha in 2015 to 368 ha in 2015. The MVC decreased slightly from 275 ha in 2015 to 212 ha in 2020. Non-vegetation cover—Intertidal mudflats (NVC1)—LVC, and high vegetation cover (HVC) increased slightly from 2015 (326 ha, 291 ha, and 249 ha, respectively) to 2020 (368 ha, 292 ha, and 298 ha, respectively). By 2022, NVC2, MVC, and HVC remained unchanged, while NVC1 and LVC increased slightly from 368 ha and 292 ha in 2015, respectively, to 380 ha and 302 ha, respectively. The increase in vegetation cover and the natural regeneration of mangrove species were partly due to the adaptation of mangrove species to the site (river mouth areas), particularly the protection provided by Ngang Island offshore, and the construction of these structures. In addition, these structures were constructed in a rather stable area (slightly eroded and estuarine area) and therefore have yet to provide any noticeable benefits for mangrove regeneration three to five years after their construction. In the future, the morpho dynamic and hydrodynamic elements of the site should be adequately considered during the design and construction of these structures to increase vegetation cover and promote natural mangrove regeneration. Full article

Scyphiphora hydrophyllacea is an endangered mangrove species in China. Over-exploitation and coastal development have drastically reduced its distribution and population, now limited to the Qingmei Port (Sanya) and the Qinglan Port (Wenchang). Despite its critical status, research on its ecological roles remains limited. This study examines the characteristics of S. hydrophyllacea communities and their relationship with soil properties. A total of 17 species from 11 families and 14 genera were recorded. TWINSPAN classification identified two distinct community types: the Qinglan Port community and the Qingmei Port community. Significant biodiversity differences were found only in the tree layer, with no differences in shrub or herbaceous layers. The importance value of S. hydrophyllacea within the arbor layer exhibited variability across the two communities, serving as an associated species in the Qinglan Port community and as a dominant species in the Qingmei Port community, suggesting potential barriers to its natural regeneration. Redundancy analysis (RDA) revealed that key soil factors influencing S. hydrophyllacea’s distribution include electrical conductivity (EC), total phosphorus (TP), total nitrogen (TN), soil organic content (SOC), and carbon/nitrogen ratio (C/N). We propose that high soil salinity and nitrogen deficiency may act as key factors limiting the natural regeneration of S. hydrophyllacea. Full article

Mangroves are vital intertidal ecosystems that support biodiversity and protect coastal communities, but face increasing pressure from anthropogenic activities that sustain local livelihoods. It is crucial to integrate the social dimension into conservation efforts by encouraging community participation in mangrove restoration. Chame Bay, located on the central Pacific coast of Panama, is a protected area with significant mangrove cover, but despite its management plan, degradation continues due to intensive timber extraction for charcoal production and insufficient natural regeneration. This study investigates local knowledge and perceptions of mangrove functions and regeneration. A proportional stratified sampling of the Chame Bay population was used, with 300 interviews conducted among key stakeholders, including residents and mangrove resource users. Variables such as age, education, and profession were analyzed in relation to perceptions, participation, and willingness to participate in restoration efforts. Results indicate that 24.67% of the population’s primary economic activity is charcoal production from mangrove wood, with 15% of producers already involved in restoration and 60% willing to participate. These findings highlight the potential for community-driven restoration and emphasize the need for environmental education to encourage participation. This study provides essential information for designing restoration strategies in mangrove areas in Central America. Full article

Palmate-leaved morning glory (Ipomoea cairica (L.) Sweet) is a fast-growing perennial herbaceous twining vine that was recently discovered to invade mangrove wetlands in China. To understand the mechanism of its successful invasion, the salt tolerance of a coastal ecotype from Zhuhai and a terrestrial ecotype from Guangzhou were compared under salt stress. The morphological, physiological, and biochemical parameters related to growth, ion homeostasis, photosynthetic pigments, chlorophyll fluorescence parameters, oxidative stress, and apoptosis were measured in both ecotypes. Monitoring apoptosis showed that the protoplasts of the coastal ecotype underwent apoptosis and were later compared with those of the terrestrial ecotype. The coastal ecotype was also found to have higher regenerated stems; less water loss, sodium (Na⁺) uptake, and membrane damage; higher salt gland density and area; and better photosynthetic performance than the terrestrial ecotype. The coastal ecotype probably prevented salt-related damage by reducing its water loss and secreting excess Na⁺ through its lower stomatal density and higher density and area of salt glands. The coastal ecotype also maintained a better balance of Na⁺, potassium ions, nitrogen, and phosphorus under salt stress. Moreover, the coastal ecotype had higher activities of antioxidant enzymes, including superoxide dismutase, peroxidase, and catalase, and a higher content of non-enzymatic antioxidants, including proline and anthocyanins, which indicate a stronger antioxidant ability. Our results suggest that the coastal ecotype adapts to a higher salt tolerance than the terrestrial ecotype by enhancing its exclusion of salt, adjusting its osmolytes, and through photosynthetic efficiency, which could explain its successful invasion in the mangrove wetland ecosystem. Full article

Following the largest forest fire in Vietnam in 2002, various activities were undertaken to sustain the mangrove forest on peat soil remnants in the Mekong Delta region. These activities included promoting natural regeneration, afforestation, and rapid forest restoration measures, in addition to other protective measures such as rainwater retention to maintain moisture levels for fire prevention. However, two critical challenges emerged: allowing the forest to naturally regenerate would lead to annual forest fires but maintaining a constant water level through year-round water retention would harm biodiversity. The study was conducted in U Minh Thuong National Park to address forest regeneration. After a major forest fire in Vietnam, various measures were taken to promote forest regeneration, including afforestation, silvicultural solutions, and hydrological techniques such as rainwater storage to maintain humidity and prevent future fires. A hand drill was used to collect samples, and a total of 15 plots were set up to survey the growth of the forest at three peat thickness levels. At each of the three collection sites, samples of one kg were collected and labeled according to the site as UTM1, UTM2, and UTM3. The samples were then sent to the laboratory of the Southern Institute of Forestry Science for analysis. There was a relationship between the chemical indicators of peat and the evolution of the Melaleuca forest. Peat thickness and flooding regime significantly influenced the growth of the Melaleuca forest, while another identified relationship was between peat chemical indicators and forest growth. The chemical composition of peat water changed significantly due to the rainy and dry seasons, with nutrient content and pH affecting forest growth. Peat thickness and flooding regime were essential in regulating forest growth. These studies highlight the importance of considering multiple factors, such as peat thickness and chemical properties, when developing effective forest restoration strategies. By understanding the relationship between peat thickness, chemical properties, and forest growth, forest managers can develop targeted strategies to promote regeneration while minimizing negative impacts on biodiversity. Full article

The Amazon Macrotidal Mangrove Coast contains the most extensive and continuous mangrove belt globally, occupying an area of ~6500 km² and accounting for 4.2% of global mangroves. The tallest and densest mangrove forests in the Amazon occur on the Bragança Peninsula. However, road construction that occurred in 1973 caused significant mangrove degradation in the area. A spatial-temporal analysis (1986–2019) based on optical, Synthetic Aperture Radar (SAR), drone images, and altimetric data obtained by photogrammetry and validated by a topographic survey were carried out to understand how the construction of a road led to the death of mangroves. The topographic data suggested that this road altered the hydrodynamical flow, damming tidal waters. This process killed at least 4.3 km² of mangrove trees. Nevertheless, due to natural mangrove recolonization, the area exhibiting degraded mangrove health decreased to ~2.8 km² in 2003 and ~0.73 km² in 2019. Climatic extreme events such as “El Niño” and “La Niña” had ephemeral control over the mangrove degradation/regeneration. In contrast, the relative sea-level rise during the last several decades caused long-term mangrove recolonization, expanding mangrove areas from lower to higher tidal flats. Permanently flooded depressions in the study area, created by the altered hydrodynamical flow due to the road, are unlikely to be recolonized by mangroves unless connections are re-established between these depressions with drainage on the Caeté estuary through pipes or bridges to prevent water accumulation between the road and depressions. To minimize impacts on mangroves, this road should have initially been designed to cross mangrove areas on the highest tidal flats and to skirt the channel headwaters to avoid interruption of regular tidal flow. Full article

The short- to long-distance dispersal (SDD and LDD) of propagules is critical for the regeneration of mangrove forests. Mark–recapture experiments are considered to be a good tool for assessing such dispersal patterns. However, dense mangrove roots, exposed mudflats, shallow water, etc. often limit the number of recaptured propagules and their implication studies. Therefore, a combination of hydrodynamic and particle tracking models, together with a mark–recapture experiment, were applied to identify the dispersal behavior of Rhizophora mucronata Lamk. propagules in a coastal lagoon of Setiu Wetlands, Malaysia. The transport trajectories revealed that the dispersal of propagules is leptokurtic, with majority of them confined to very-short-distance dispersal (VSDD; 3–5 m) to SDD (1400 m). While higher obstacle density (e.g., mangrove roots) constrained the propagule dispersal, weaker tidal currents that coupled with less upstream discharge increased their retention time and settlement closer to the point of release. Under this scenario, the chances for propagules to exit from the lagoon mouth and their entry into the open waters for LDD are very limited. These results can explain the abundance of Rhizophora spp. in the northern sector of the Setiu Wetlands and be useful for species-level conservation/management. Full article

Coastal wetlands are restored to regenerate lost ecosystem services. Accurate and frequent representations of the distribution and area of coastal wetland communities are critical for evaluating restoration success. Typically, such data are acquired through laborious, intensive and expensive field surveys or traditional remote sensing methods that can be erroneous. Recent advances in remote sensing techniques such as high-resolution sensors (<2 m resolution), object-based image analysis and shallow learning classifiers provide promising alternatives but have rarely been applied in a restoration context. We measured the changes to wetland communities at a 200 ha restoring coastal wetland in eastern Australia, using remotely sensed Worldview-2 imagery, object-based image analysis and random forest classification. Our approach used structural rasters (digital elevation and canopy height models) and a multi-temporal technique to distinguish between spectrally similar land cover. The accuracy of our land cover maps was high, with overall accuracies ranging between 91 and 95%, and this supported early detection of increases in the area of key ecosystems, including mixed she-oak and paperbark (10 ha), mangroves (0.91 ha) and saltmarsh (4.31 ha), over a 5-year monitoring period. Our approach provides coastal managers with an accurate and frequent method for quantifying early responses of coastal wetlands to restoration, which is essential for informing adaptive management in the regeneration of ecosystem services. Full article

Mangroves are critical to maintaining human well-being and global biodiversity. Eastern and western African shores present major environmental contrasts that reflect on mangrove forests’ structure and the ecosystem services they provide to human communities. This study compares the mangrove forest structure and condition, ecosystem services, and uses of resources in Maputo Bay (Mozambique in eastern Africa) and Príncipe Island (São Tomé and Príncipe in western Africa). Five mangrove species were identified in Maputo Bay, Avicennia marina, Bruguiera gymnorhiza, Ceriops tagal, Rhizophora mucronata, and Xylocarpus granatum, and the importance value index was higher for A. marina. Mangroves in Príncipe were exclusively dominated by Rhizophora harrisonii. In Maputo Bay, a weak regeneration characterized by a low quantity of seedlings was observed, although in Príncipe the sites were characterized by a low regeneration rate but well-established forests. The comparison of the mangrove structure between Maputo Bay and Príncipe Island presented statistically significant differences for mean DBH and height, whereas the trees in Príncipe presented higher values for both parameters. Strong human disturbance (through cutting) was identified in almost all sites in Maputo Bay but was rarely observed on Príncipe Island. In Maputo Bay, more than 90% of the coastal human community is involved in activities related to the surrounding mangroves, with a diversified exploitation of forest resources. On Príncipe Island, the exploitation of mangroves targets only tannin from the mangrove bark to dye fishing nets and small boats. The economic value of mangroves in Maputo Bay has subsistence and commercial importance, in contrast to Príncipe, which revealed no major economic value to the community. Full article

We used publicly available land-cover datasets (1921, 1947, 1976, 1992, 2001, 2006, 2014) to assess land-cover change on Babeldaob Island, Republic of Palau. Land-cover data were organized, classified, and summarized by area and percentage of island cover for forest, mangrove, non-forest vegetation, and non-vegetation. Japanese colonial administration of the island between 1921 and 1947 included industrial mining and agriculture, which reduced total non-mangrove forest cover by 16%. Temporal vegetation cover dynamics from 1947 through 2014 indicate unassisted forest regeneration of 12% with a concomitant decrease in non-forest vegetation including abandoned agriculture, the majority of which happened by 1976. Mangrove cover appears to have remained stable throughout the 93 year study period. Ground-truth observations showed the highest rates of vegetation cover change since 1976 for non-vegetated areas, followed by marsh and swamp forest. The proportion of non-vegetated cover increased at least twofold after WWII, with at least half comprising roads. Contrary to other tropical geographies, we saw forest expansion following completion of a major perimeter road. However, the larger landscape is permeated by dynamic forest edges subject to wildfire and other land-use disturbances. Full article

Avicennia marina (Forssk.) Vierh. is an important mangrove species that inhabits the outermost zone of mangrove forests, but it has been shown to have a poor ability to regenerate due to its low seedling quality. We conducted a study to evaluate the specific growth requirements of A. marina, i.e., medium and salinity level. Germinated seeds were transplanted to pots filled with media, i.e., silt loam (M1), loam (M2), sandy loam (M3), or sand (M4), with various salinity levels 5 (S1), 5–15 (S2), 15–25 (S3), or 25–35 ppt (S4). Survival rate, growth, biomass partition, and seedling quality were observed for 14 weeks after transplanting the seeds. The highest rate of seedling survival was found in the S2 condition, and higher concentrations of salinity lowered the survival rates. The S1 treatment promoted the initial 8 week growth of the seedlings. Growth medium had no significant effect, except on the survival rates grown in M4. Growth medium composition had no distinct effect on seedling growth. The S2 and S3 treatments induced better growth (in terms of shoot height and root length) and resulted in high-quality (i.e., Dickson quality index) seedlings in any type of medium. The S3 treatment increased the seedling quality in M1 and M4, whereas the S4 treatment only benefited seedlings in the M4 medium. According to the results, a specific range of salinity (5–15 ppt) with circulated water in any type of medium is recommended for the establishment of an ex situ nursery for the propagation of A. marina, in contrast to the general range of salinity (4–35 ppt) stated in previous references. Full article

Mangrove forests are increasingly threatened by plant invasions worldwide, but some mangrove species are invasive and threaten salt marsh and native mangrove ecosystems. The southern coast of China is invaded by the cordgrass Spartina alterniflora, and the mangrove Sonneratia apetala, providing a model system for studying the processes and mechanisms through which non-native species establish and spread. We used a transplant experiment to test the overarching hypothesis that native herbivores and plants provided biotic resistance against invasion by S. apetala, and that the importance of these factors would vary geographically. Survival of transplanted mangrove seedlings was lower in Zhangjiang Estuary (23°55′ N) than in Leizhou Bay (20°56′ N), and varied with species and habitats. S. apetala had higher survival and growth rates than native mangroves at both sites, and S. apetala grew taller than the S. alterniflora canopy at Leizhou Bay in only two growing seasons. In contrast, native mangroves grew poorly in S. alterniflora. Grazing by rodents and insects suppressed the growth and survival of Kandelia obovata and Avicennia marina in Zhangjiang Estuary and Leizhou Bay, but had little effect on S. apetala. Competition with vegetation (S. alterniflora and native mangroves) exacerbated the reduced survival of native mangroves, and these effects varied across study sites. Low survival of non-native S. apetala in vegetated habitats at Zhangjiang Estuary was likely due to a synergistic effect of low winter temperatures and low light intensity. Escape from herbivory (the opposite to biotic resistance) and fast growth may drive the quick expansion of non-native S. apetala in China. Rapid encroachment of S. apetala may transform the native mangrove forests and monospecific intertidal Spartina grasslands into non-native mangrove forests in the southern coast of China. Full article