Well-intentioned, but poorly implemented: Debris from coastal bamboo fences triggered mangrove decline in Thailand

Evaluating the effectiveness of Mangrove rehabilitation: A novel approach for sustainable coastal management

We used UAV-LiDAR technology and other advanced remote sensing techniques to evaluate mangrove rehabilitation projects along the eroding shoreline of the Upper Gulf of Thailand. Our results delineate the necessary biophysical conditions for successfully rehabilitating mangroves, establishing optimal conditions under which mangroves can naturally re-establish and thrive. Furthermore, we investigated the effectiveness of different coastal defense structures in fostering mangrove recolonization. Our analysis shows that nearshore breakwaters markedly outperform submerged breakwaters and bamboo fences, with a success rate of over 65% by significantly reducing wave energy that aids sediment trapping. These findings suggest that refinements in the configuration of coastal structures, including the elevation of breakwater crests and selective deployment of bamboo fences, will enhance mangrove rehabilitation success. These insights affirm the role of UAV-LiDAR surveys for optimizing mangrove restoration initiatives, thereby facilitating sustainable development for coastlines plagued by erosion. The insights gleaned offer a blueprint for bolstering the success rate of mangrove rehabilitation projects, directing them toward sustainable coastal development.

Ecological ramifications of marine debris in mangrove ecosystems: Estimation of substrate coverage and physical effects of marine debris on mangrove ecosystem in Negombo Lagoon, Sri Lanka

The adverse environmental impacts on mangrove ecosystems due to anthropogenic marine debris contamination have attracted public attention not only in Sri Lanka but worldwide. Therefore, quantification of marine debris in sensitive ecosystems like mangroves is critical to assess the impacts on ecosystem vitality and services. We conducted this study to assess the abundance and density of marine debris in Negombo lagoon, Western Province, Sri Lanka. We selected two sites (n = 2) using the purposive sampling technique. Marine debris cover and concentration were calculated to explore the extent of pollution from marine debris. The findings revealed that 9.83 ± 1.05 % of the substrate of the mangrove ecosystem is covered by debris. Nine types of marine debris were recorded, and a higher abundance belonged to single-use plastic items. A significantly higher debris cover was found in Kadolkele (18.80 ± 1.74 %, n = 120) than in Molekadolwetiya (0.85 ± 0.03 %, n = 120) (One-way ANOVA, p < 0.05). The study indicated that the mangroves in lagoon are highly polluted with marine debris and act as "litter catchers." Correlation coefficient analysis was used to find the impact of debris cover on physical damage to roots, seedlings, and undergrowth vegetation. Correlation analysis revealed that physical damage to seedlings and branches/barks have a positive correlation with debris cover. To conserve these valuable coastal habitats in Negombo lagoon, it is recommended to take remedial measures to reduce arriving debris loads and to remove the debris present in mangroves.

Anthropogenic debris pollution in peri-urban mangroves of South China: Spatial, seasonal, and environmental drivers in Hong Kong

Excessive mismanaged debris along tropical coasts pose a threat to vulnerable mangrove ecosystems. Here, we examined the spatial, seasonal and environmental drivers of anthropogenic debris abundance and its potential ecological impact in peri-urban mangroves across Hong Kong. Seasonal surveys were conducted in both landward and seaward zones, with identification, along belt transects, of macrodebris (>5 mm) based on material type and use. Our results indicate spatial variability in debris abundance and distribution, with plastic being the predominant material type identified. Both plastic and non-plastic domestic items covered the most surface area. Debris aggregation was highest at the landward zones, consistent with the literature. In the dry season, more debris accumulated and covered greater surface area in both seaward and landward zones. These results confirm that land-derived debris from mismanaged waste, rather than debris coming from the Pearl River, is the primary source of anthropogenic debris pollution threatening Hong Kong's mangroves.

Landward zones of mangroves are sinks for both land and water borne anthropogenic debris

The hotspots for mangrove diversity and plastic emissions from rivers overlap in Asia, however very few studies have investigated anthropogenic marine debris (AMD) pollution in these threatened coastal ecosystems. Despite Hong Kong's position at the mouth of the Pearl River, a major source of mismanaged waste in Asia, the mangroves in Hong Kong have never been extensively surveyed for AMD. Here we assessed the patterns of AMD abundance within 18 mangrove forests across Hong Kong surveying both their landward and seaward zones. We recorded and categorised, according to their material and potential uses, both the amount of debris items and area they covered, to better quantify its potential impact on the mangroves. Across Hong Kong mangroves, the average abundance of debris was 1.45 ± 0.38 (SE) items m^-2, with an average coverage of 6.05 ± 1.59%. Plastic formed a high proportion of AMD accounting for 70.31% by number of items and 49.71% by area covered, followed by glass/ceramics and wood/bamboo. Disposable food packaging, fishing gear and industrial and construction related waste were the major sources of AMD we documented. On average, we recorded about six times more debris items m^-2 at the landward sites than at the seaward one, but these abundances varied between the East and the West coastlines of Hong Kong. Our data confirms the hypothesis that landward areas of mangrove forests act as traps and retain marine borne debris, but they also suggest that direct dumping of waste from the land could represent a serious impact for these forests placed in between the land and the sea. More research is needed to ascertain the impact of land disposed debris on mangrove degradation, and this study strongly advocates for a cultural shift about the perception of these forests by the public.

Mangroves as unique but understudied traps for anthropogenic marine debris: A review of present information and the way forward

Marine debris and plastic pollution affect all coastal habitats, however coastal debris studies are predominantly performed on sandy beaches. Other coastal habitats, such as mangroves, remain understudied. Eighteen of the top twenty rivers that contribute the most plastic to the ocean are associated with mangroves, but very few of those forests were investigated in terms of plastic debris pollution. Here we discuss the results of the few available studies on macrodebris conducted in mangroves, which show that mangrove debris research is still in its early stages, with many areas of study to be further investigated. Indeed, the distinct structural complexity of mangroves increases their ability to trap debris from both terrestrial, freshwater and marine sources, resulting in impacts unique to the mangrove ecosystem. Our review highlights a significant lack in standardisation across the performed surveys. Here we suggest standardised guidelines for future integrated macrodebris and microplastic studies in mangroves to facilitate comparisons between studies. Such standardisation should prioritize the use of stratified random sampling, the measurement of the area covered by the debris and the abundance and type of macrodebris and microplastics found, in order to assess the ecological impact of macrodebris and its role as source of microplastics for adjacent ecosystems. We also advocate the use of standard categories across studies, based on those identified for surveying other coastal habitats. This review highlights an alarming knowledge gap in extent, sources and overall impacts of marine macrodebris, mainly constituted by plastic, on mangrove forests, which hinders policy making to address this issue. Standardised, reliable and extended research on this aspect of mangrove pollution is needed to manage and protect these endangered vegetated coastal ecosystems.

Mapping Large-Scale Mangroves along the Maritime Silk Road from 1990 to 2015 Using a Novel Deep Learning Model and Landsat Data

Mangroves are important ecosystems and their distribution and dynamics can provide an understanding of the processes of ecological change. Meanwhile, mangroves protection is also an important element of the Maritime Silk Road (MSR) Cooperation Project. Large amounts of accessible satellite remote sensing data can provide timely and accurate information on the dynamics of mangroves, offering significant advantages in space, time, and characterization. In view of the capability of deep learning in processing massive data in recent years, we developed a new deep learning model—Capsules-Unet, which introduces the capsule concept into U-net to extract mangroves with high accuracy by learning the spatial relationship between objects in images. This model can significantly reduce the number of network parameters to improve the efficiency of data processing. This study uses Landsat data combined with Capsules-Unet to map the dynamics of mangrove changes over the 25 years (1990–2015) along the MSR. The results show that there was a loss in the mangrove area of 1,356,686 ha (about 21.5%) between 1990 and 2015, with anthropic activities such as agriculture, aquaculture, tourism, urban development, and over-development appearing to be the likely drivers of this decline. This information contributes to the understanding of ecological conditions, variability characteristics, and influencing factors along the MSR.