Mangrove distribution and afforestation potential in the Red Sea

Reforestation potential for integrated mangrove aquaculture target at realizing a synergy of ecological and economic benefits

Integrated mangrove aquaculture is a viable approach to achieving mangrove ecological restoration and enhancing the economic benefits of aquaculture. In this study, a novel decision-making framework was developed to optimize site selection for the conversion of low-economic-performance aquaculture ponds into integrated mangrove aquaculture systems. This framework was established through the integration of a habitat suitability model and social cost analysis, ensuring both ecological feasibility and economic viability. As a key component, a remote sensing-based interpretation method was introduced to identify abandoned aquaculture ponds, with the objective of minimizing social costs associated with land-use transitions. Subsequently, the intertidal zone was delineated using the similar slope angle principle, and habitat suitability was assessed through Maxent niche modeling, incorporating key environmental limiting factors. The proposed framework was applied across five coastal provinces in China. Results indicated that Mangrove distribution was primarily influenced by bioclimatic variables, with temperature identified as the most critical determinant, followed by precipitation, and to a lesser extent, topography and salinity. A total of 1610 ha of abandoned coastal aquaculture ponds within the intertidal zone were classified as medium-to-high suitability for reforestation into a mangrove-aquaculture coupled system, representing 8.9 % of the total assessed area. This study provides comprehensive insights into mangrove habitat suitability and identifies priority areas for restoration efforts in the intertidal zones of coastal provinces. The findings underscore the importance of environmental variables in shaping mangrove distribution, offering a scientific basis for coastal management and ecological restoration strategies.

Geospatial distribution and anthropogenic litter impact on coastal mangrove ecosystems from the Saudi Arabia coast of the Gulf

Mangrove ecosystems are significantly impacted by marine litter pollution, an increasingly important environmental problem. These ecosystems, situated at the interface between sea and land, serve as critical habitats and act as traps for plastic pollution. This study investigated the concentration, source, and composition of marine litter on both the mangrove bottom and canopy along the Saudi Arabia coast in the Gulf. The observed concentration of surface litter ranged from 0.98 ± 0.05 to 2.96 ± 0.25 items/m², with a mean concentration of 1.4 ± 0.61 items/m² (SD; N = 9). The mean trapped litter was 0.79 ± 0.45 items/tree, ranging from 0 to 7 items/tree. Plastic litter dominates the mangrove environment, accounting for 80% of debris items on the floor and 43% of those entangled in the canopy. Single-use plastics were the most prevalent type of litter detected across all surveyed locations. The sediments within the mangrove ecosystem serve as long-term repositories for plastic litter, evaluated through various indices, such as General Index, Clean Coast Index, Pollution Load Index, and Hazardous Litter Index, to assess the cleanliness of the mangrove floor. The Pollution Load Index shows a "Hazard level I," indicating that the mangrove floor is less contaminated. A higher concentration of litter was observed in urban areas with greater population density, likely originating from terrestrial activities like urban runoff and marine activities, particularly fishing.

Climate change challenges coastal blue carbon restoration in China

Coastal blue carbon has become an emerging natural climate solution (NCS) that offers significant potential for mitigating global climate change while providing various ecosystem services. However, blue carbon ecosystems, including mangroves, tidal salt marshes, and seagrass meadows, are susceptible to the impacts of climate change, which in turn affects their potential to mitigate climate change. In this study, we employed the MaxEnt to evaluate the potential suitable areas and carbon sink potential of China's Coastal blue carbon ecosystem under three climate scenarios for the present and projected conditio ns in 2050. Our results reveal that China's coastal blue carbon ecosystems have an estimated carbon sequestration potential of 8.65 ∗ 105 t/a. Specifically the potential annual carbon sequestration of mangroves is 1.457 ∗ 105 t/a, tidal salt marshes is 6.714 ∗ 105 t/a, and seagrass is 4.769 ∗ 104 t/a. By 2050, due to climate change, the annual carbon sequestration potential of China's coastal blue carbon is projected to decrease by 0.733-2.351 ∗ 105 t/a, representing an 8-27 % reduction from the current levels. Furthermore, the distribution of potential suitable areas for these blue carbon ecosystems is expected to shifted to different degrees, among which the potential suitable areas of mangrove will be transferred to the greatest extent, showing a trend of northward expansion. Future conservation and restoration efforts for blue carbon ecosystems ought to consider the impact of climate change and fully utilize the potential of blue carbon.

Green turtle tracking leads the discovery of seagrass blue carbon resources

Seagrass meadows are natural carbon sinks, and their conservation and restoration play a crucial role in climate change mitigation and adaptation. However, blue carbon projects are hindered, in most nations, by major gaps in understanding the distribution and extent of seagrasses. Here, we show how satellite tracking of green turtles (Chelonia mydas) provided a major advance in identifying novel seagrass blue carbon resources in the Red Sea. By tracking 53 nesting green turtles, we identified 38 distinctive foraging sites. All ground-truthed foraging sites (100%) identified a seagrass meadow, surpassing the 40% (n = 30) accuracy of satellite imagery-based inferences. Sampling from these turtle-derived locations represents a greater range of depths than previously sampled in the Red Sea providing a carbon stock estimate of 4.89 ± 0.83 kg Corg (organic carbon) m-2. By improving estimates of seagrass extent and associated blue carbon, our approach can support the conservation of blue carbon resources in data-deficient regions worldwide.

Investigating the bacterial community of gray mangroves (Avicennia marina) in coastal areas of Tabuk region

Mangrove vegetation, a threatened and unique inter-tidal ecosystem, harbours a complex and largely unexplored bacterial community crucial for nutrient cycling and the degradation of toxic pollutants in coastal areas. Despite its importance, the bacterial community composition of the gray mangrove (Avicennia marina) in the Red Sea coastal regions remains under-studied. This study aims to elucidate the structural and functional diversity of the microbiome in the bulk and rhizospheric soils associated with A. marina in the coastal areas of Ras Alshabaan-Umluj (Umluj) and Almunibrah-Al-Wajh (Al-Wajh) within the Tabuk region of Saudi Arabia. Amplicon sequencing targeting the 16S rRNA was performed using the metagenomic DNAs from the bulk and rhizospheric soil samples from Umluj and Al-Wajh. A total of 6,876 OTUs were recovered from all samples, of which 1,857 OTUs were common to all locations while the total number of OTUs unique to Al-wajh was higher (3,011 OTUs) than the total number of OTUs observed (1,324 OTUs) at Umluj site. Based on diversity indices, overall bacterial diversity was comparatively higher in rhizospheric soil samples of both sites. Comparing the diversity indices for the rhizosphere samples from the two sites revealed that the diversity was much higher in the rhizosphere samples from Al-Wajh as compared to those from Umluj. The most dominant genera in rhizosphere sample of Al-Wajh were Geminicoccus and Thermodesulfovibrio while the same habitat of the Umluj site was dominated by Propionibacterium, Corynebacterium and Staphylococcus. Bacterial functional potential prediction analyses showed that bacteria from two locations have almost similar patterns of functional genes including amino acids and carbohydrates metabolisms, sulfate reduction and C-1 compound metabolism and xenobiotics biodegradation. However, the rhizosphere samples of both sites harbour more genes involved in the utilization and assimilation of C-1 compounds. Our results reveal that bacterial communities inhabiting the rhizosphere of A. marina differed significantly from those in the bulk soil, suggesting a possible role of A. marina roots in shaping these bacterial communities. Additionally, not only vegetation but also geographical location appears to influence the overall bacterial composition at the two sites.

Simulation of mangrove suitable habitat in the Guangdong-Hong Kong-Macao Area under the background of climate change

Climate change has resulted in great influence on the geographical distribution of species. Mangrove forests are one of the most precious ecosystems on the planet, yet they are being threatened by the habitat destruction and degradation under the situation of global warming. Seeking suitable areas for planting mangroves to tackle climate change has been gradually popular in ecological restoration. In this study, we applied the Maximum Entropy algorithm to assess the contribution of environmental factors on mangrove distribution, simulated mangrove suitable habitat for present and future (scenario of SSP245-2070s), and used kernel density analysis for identifying priority of mangrove reserve construction. Results indicate that mean diurnal range and elevation made the highest contribution on mangrove distribution. At present, the mangrove habitat suitability along the western coast of the Guangdong-Hong Kong-Macao Area (GHMA) was the highest while that along the eastern coast was the lowest. By 2070s, mangrove suitable areas would show a decreasing trend under SSP245 scenario. High suitable areas (HSAs) would change fastest and shift to northeast in the same direction as dominant environmental factors. For further mangrove restoration, it is advisable to select sites with high suitability density in the future but low reclamation density at present as prior mangrove reserves, and these sites distribute along the northeastern and northwestern coast of Zhanjiang, Yangjiang and Jiangmen, the Pearl River Estuary and Honghai Bay of Shanwei. Meanwhile, regions with lower suitability density but higher reclamation density could be listed as secondary mangrove reserves.

Environmental flow assessment for intermittent rivers supporting the most poleward mangroves

The most vulnerable and dynamic ecosystems in terms of response to climate change and fluctuations in hydrological conditions are mangroves, particularly those located on the edge of their latitudinal range limits. The four primary Iranian mangrove forest sites: Nayband, Qeshm, Gabrik, and Govatr, located in the northern part of the Persian Gulf and the Gulf of Oman already exist near the limit of their tolerance to extreme temperature, precipitation, and salinity. Due to extreme climate conditions at these locations, the mangrove trees are usually smaller and less dense as compared with mangroves closer to the equator complicating their monitoring and mapping efforts. Despite the growing attention to the ecological benefits of mangrove forests and their importance in climate change mitigation, there are still a few studies on these marginal mangroves. Therefore, we investigated whether the variation in mangrove ecosystem health is related to the changes in physical parameters and differs between estuarine and sea-side locations. We developed a comprehensive database on NDVI values, associated rainfall, temperature, and river flow based on in-situ and remote sensing measurements. By understanding the normal hydrologic patterns that control the distribution and growth of mangroves in arid and semi-arid regions, we are questioning the need for environmental flow allocation to restore mangrove ecosystem health. This brings us to the second gap in the literature and the need for further studies on Environmental Flow assessment for intermittent and ephemeral rivers. Alike other mangroves studied, forests showed greenness seasonality, positively correlated with rainfall, and negatively correlated with temperature. As there was no clear difference between estuarine and marine sites, freshwater influence in the form of river flow, unlike temperature, cannot be considered a major limiting factor. Nevertheless, during prolonged droughts mangroves could benefit from the recommended allocation of Environmental Flow during the cold period (November-March).

Mangrove interaction with saltmarsh varies at different life stages

Mangroves and saltmarshes are two of the most relevant coastal habitats for humans. These ecosystems offer several services like coastal protection, climate mitigation, and nursery habitats for many artisanal and commercially exploited fish, crabs, and shellfish. They mostly dominate different latitudinal ranges but in several places around the world they co-occur and interact. Here, we summarize the current scientific knowledge on mangrove-saltmarsh ecological interactions and propose a conceptual model. We screened 1410 articles from 1945 to 2022 and selected 29 experiments that assessed mangrove-saltmarsh ecological interactions. Both positive and negative interactions are observed but there is variation along different mangrove life stages. Higher retention and establishment of mangrove propagules are found inside saltmarshes than on bare flats, i.e. facilitation, and these effects are higher at grass than at succulent saltmarsh species. Mangrove seedlings, saplings, or trees mostly compete with saltmarshes, negatively affecting mangrove growth. We propose a model with different outcomes considering the interaction between different mangrove's life stages and saltmarsh forms and discussed these interactions in the light of anthropogenic threats and climate change.

Understanding the natural expansion of white mangrove (Laguncularia racemosa) in an ephemeral inlet based on geomorphological analysis and remote sensing data

The interactions between local tides and river discharges are crucial in the processes related to the recruitment of mangrove propagules in estuarine systems. This investigation aimed to determine the causes of the recent natural recruitment and expansion of Laguncularia racemosa in mudflats within an ephemeral inlet in Mexico. We conducted a fluvial and coastal geomorphology assessment with spaceborne and UAV-based images. We deployed and recorded continuous data loggers in the estuarine system to assess water level and salinity. Depending on the available data, we used a combination of cloud-computing Google Earth Engine, UAV-Digital Surface Models, LiDAR, Google Earth images, and biophysical variables to monitor mangrove forests from 2005 to 2022. When the inlet is open, the estuarine system presents a full tidal range (∼1-1.5 m) with a strong salinity gradient (0-35 mS/cm), in contrast to the strong freshwater influence and minimal water level variability (<10 cm) that prevails for three months when the inlet is closed. Once the mouth of the river closes, there is considerable sediment accumulation, creating mudflat areas adjacent to the mangrove forests where Laguncularia racemosa propagules begin to establish under minimal water level variability and oligohaline conditions. After 16 years, the new forest expanded by 12.3 ha, presenting a very high density (10000 stems/ha), a considerable basal area (54-63 m2/ha), and a maximum canopy height of 15.8 m, which largely surpasses that of other semiarid Laguncularia racemosa forests within permanent open-inlet systems or even in ephemeral inlets with different hydrological conditions. Our study will help to understand the causes of natural Laguncularia racemosa recruitment in extremely dynamic systems.