Coastal Protection Research Articles

Cost‐efficiency and effectiveness of coral restoration pathways

Coral reefs play a crucial role in supporting over half a billion human livelihoods through their contributions to fisheries, tourism, and coastal protection. In light of substantial global declines in coral cover and the deterioration of reef habitats due to climate change and other human‐driven influences, the urgency of coral reef restoration has escalated to help preserve their vital ecosystem services. Comprehending the economic costs associated with existing and potential future coral restoration approaches has become time‐sensitive. The median cost of coral reef restoration is estimated to be 400,000 USD/ha (at base year 2010). This estimate comes with limitations due to its reliance on reported project costs associated with various techniques. Here we look to standardize expenses through uniform costing of reported efforts based on the time invested to estimate specific per‐unit costs for restoration methods. We complement literature‐extracted values with independent estimates based on real‐world operations. Using this approach, we decipher comparative costs of different nursery and outplanting approaches and identify incorporated dependencies. To gain insights into the impact of labor costs on global coral reef restoration expenditures, we examine variations in the costs of labor in two coral reef regions. Overall, our data‐based approach identifies limitations within the most commonly practiced restoration pathways, opportunities to reduce operational costs, and points toward priorities for future research and development.

Hydrodynamic mechanisms of topographic evolution in straight sandy beach: a case study of Wanpingkou beach, China

Stricter controls on destructive human activities in recent years have improved the protection and management of sandy coasts in China. Marine-driven geomorphic changes have become the predominant process influencing future beach evolution. However, in the complex geomorphic conditions of mixed artificial and natural coastlines, the mechanisms and contributions of various marine-driven factors to beach changes remain unclear. Using methods of field observations and numerical simulations by FVCOM model, this study reveals the sedimentary dynamic mechanism of straight sandy beach in the southern Shandong Peninsula (Wanpingkou beach, WPK beach). From 2005 to 2016, the northern section of WPK Beach eroded at a rate of approximately 2-3 m/year, the middle section at about 0.5-1.5 m/year, and the southern section accrued at an average rate of about 1-2 m/year, demonstrating an overall pattern of “northern erosion and southern accretion.” During winter, the average grain size of beach sediments is about 0.5 mm with minimal variations, indicating an onshore transport trend; in summer, the average grain size is about 0.7 mm with larger variations, indicating an offshore transport trend. Offshore sediment transport correlates mainly with seasonal changes in wind direction, while alongshore sediment transport is influenced by tidal currents, wind-induced currents, and wave-induced currents. Wave-induced currents are the primary force in alongshore sediment transport with a velocity of 0.1-0.3 m/s toward southwest. Followed by tidal currents with a velocity of 0.05-0.1 m/s, and wind-induced currents with a velocity of 0-0.1 m/s, which have a relatively minor impact. Therefore, seasonal changes in beach morphology are primarily controlled by waves, while interannual variations is mainly influenced by a combination of wave-induced currents and tidal currents. With increasing efforts in beach maintenance and coastal ecological restoration in recent years, understanding the sedimentary dynamics of beaches remains of vital theoretical and practical value.

Geodynamic hazard assessment for the archaeological park-museum by the town of Nikopol

This study was conducted to establish the engineering geological and hydrogeological conditions of the site and to assess the geodynamic hazard in relation to the design and construction of the archaeological park-museum and feeder road in the town of Nikopol (Bulgaria). The studied terrain occupies a river terrace and the foot of a delluvial slope with an elevation of 23-68 m. The tasks of the study are to identify: the geological structure of the slope, the area and depth range of the landslides, the location of the slip surface, the physical and mechanical properties of the engineering geological strata, the hydrogeological conditions, the current stability of landslides, the change of slope stability under the action of various factors. The ground investigation includes analysis of archival and published information on the area; geodetic survey of the landslide; engineering geological mapping; exploratory boreholes; geophysical surveys using the VES method; testing of soil and water samples; compilation of longitudinal engineering geological profiles and slope stability analysis using the computational models. To the south of the study site the slope is affected by an ancient landslide with a volume of about 30 million m3 developed on the right valley slope of the Danube River in the section between the plateau and the river terrace. Consistent landslides occur in its lower part. Slope stability calculations show that the landslides are triggered by a rise in the groundwater level, an earthquake and undermining of the slope base. Rock-falls has developed on the steep rock slopes, composed of moderately to highly weathered and fractured cherty and glauconitic limestones. The size of the rockfall blocks is in the range 0.3-0.8 m3 and their transport distance reaches from 10 m to 50 m from the base of the slope. Stabilization measures and facilities are proposed to strengthen the landslides and rockfalls in the considered section of the slope. For the landslides it is proposed to implement a counterfort embankment on which to build the feeder road, drainage ribs and drainage ditches. For protection of the buildings from collapsing rock debris, an anchored high-strength net is recommended. The design takes into account the trajectory of the falling blocks and their kinetic energy. For monitoring the condition of the landslides and rockfalls, as well as for evaluating the effectiveness of the implemented strengthening, drainage and coastal protection structures, a control and measurement system for regime observation was built.

Structural Performance of GFRP-Wrapped Concrete Elements: Sustainable Solution for Coastal Protection

Protecting coastal regions is crucial due to high population density and significant economic value. While numerous strategies have been proposed to mitigate scouring and protect coastal structures, existing techniques have limitations. This paper introduces a novel approach, SEAHIVE®, which enhances the performance of engineered structures by utilizing hexagonal, hollow, and perforated concrete elements externally reinforced with glass fiber-reinforced polymer (GFRP). Unlike conventional steel bars, GFRP offers superior durability and requires less maintenance, making it a sustainable solution for any riverine and coastal environment. SEAHIVE® aims to provide robust structural capacity, effective energy dissipation, and preservation of natural habitats. Although some research has addressed energy dissipation and performance in riverine and coastal contexts, the structural performance of SEAHIVE® elements has not been extensively studied. This paper evaluates SEAHIVE® elements reinforced with externally bonded GFRP longitudinal strips and pretensioned GFRP transverse wraps. Testing full-size specimens under compression and flexure revealed that failure occurred when the pretensioned GFRP wraps failed in compression tests and when longitudinal GFRP strips slipped in flexure tests. Strength capacity was notably improved by anchoring the GFRP strips at both ends. These findings underscore the potential of the SEAHIVE® system to significantly enhance the durability and performance of coastal and riverine protection structures. FEM simulations provided critical insights into the failure mechanism and validated the experimental findings. In fact, by comparing FEM model results for cases before and after applying GFRP wraps under the same compression load, it was found that maximum stresses at crack locations were significantly reduced due to compression forces resulting from the presence of pretensioned GFRP wraps. Similarly, FEM model analysis on flexure samples showed that the most vulnerable regions corresponded to the locations where cracks started during testing.

Recent Developments in China’s Coastal Zone Management Legislation: An Appraisal

The coastal zone has become one of the areas with the most serious environmental problems and has concentrated conflicts between land development and protection in China. It is the choice of many countries to regulate and balance coastal resource utilization and environmental protection by legal means. However, China has not yet issued comprehensive legislation on coastal zone management at the national level, while some coastal provinces and cities have enacted local legislation. This study first systematically reviews China’s coastal zone management legislation at both the national and local levels, paying particular attention to those laws enacted in the past decade and subsequently looks into the core regimes adopted in China’s coastal zone management. From the perspective of achievements, the legislative framework of China’s coastal zone management legislation is relatively complete, with increasingly diverse legislative subjects and increasingly refined legal provisions, providing a strong normative basis for coastal zone management. Nevertheless, existing legislation also faces challenges such as insufficient systematization, inefficient coordination mechanisms and incomplete legislative content which impact the practical effectiveness of coastal zone management legislation. Based on China’s national conditions, this study proposes two suggestions for future improvements. On one hand, in terms of legislative principles, coastal zone legislation should embody a concept of integrated management and establish substantive principles of systematization, protection priority, prevention and precaution, justice and equality while following the principle of non-contradiction in legislative form. On the other hand, in terms of legislative content, the institutional system of China’s coastal zone management legislation should be further improved in four aspects, namely, optimizing the coordination mechanisms, introducing incentive mechanisms, strengthening public participation, and improving climate change countermeasures.

Spatiotemporal Changes and Utilization Intensity of the Zhoushan Archipelago Coastline over Four Decades

Coastal changes in China, notably in the Zhoushan Islands, have primarily been driven by coastal reclamation since the establishment of New China. This study conducted a comprehensive analysis of the Zhoushan Archipelago shoreline spanning four decades, employing remote sensing, aerial photographs, and shoreline data since 1984, along with GIS (Geographic Information System) technology. We assessed shoreline changes using the shoreline change index and shoreline artificialization index, as well as examined the influence of the Yangtze River’s suspended sediment and impoldering activities on Zhoushan’s shoreline. Furthermore, the correlation between local economic development and shoreline development was explored. The results revealed the following key findings: (1) From 1984 to 2018, the Zhoushan Archipelago shoreline decreased by 7.05 km. Temporally, the shoreline change index was −0.08%, with the most significant reduction occurring between 2008 and 2018. Spatially, differences among island groups were not pronounced. (2) The shoreline diversity index consistently increased, indicating greater diversity and complexity in shoreline use over the four decades. (3) The shoreline artificiality index steadily rose, particularly after 2000. It was highest in the south, followed by the center, and lowest in the north. (4) The intensity index of coastal land use continuously increased, with the southern island group having a higher index compared to the Zhoushan Islands. (5) The Yangtze River contributed significantly to sand inflow, influencing shoreline changes and beach shaping in Zhejiang. However, reclamation projects were identified as the primary and direct factor. (6) A positive correlation existed between Zhoushan City’s economic development and the intensity of coastal land use. This study emphasized the need for improving the control over reclamation projects and the better management of coastal protection and use. These measures could optimize resource allocation and establish a more scientific and rational coastal zone pattern.

Monitoring mangroves with multi-sensor Earth Observation data sets: from one-shot historical cartography to online and near-real-time monitoring tools

Abstract. This study outlines advancements in mangrove monitoring using Earth Observation (EO) technologies, highlighting a transition from historical cartography to modern, near-real-time monitoring systems. Mangroves, critical for biodiversity, climate regulation, and coastal protection, face threats from climate change and human activities. The need for accurate and recurrent mapping tools is emphasized, addressing the limitations of current global datasets like the Global Mangrove Watch (GMW) by incorporating high-resolution data and field measurements. The French National Research Institute for Sustainable Development (IRD) has pioneered mangrove monitoring since the 1990s, with key methodologies including the use of Sentinel-2 and Pleiades satellite imagery for high-resolution mapping, texture-based analysis, and the incorporation of LiDAR data for accurate biomass estimation. Historical cartography is contrasted with contemporary monitoring efforts, focusing on the integration of multi-source data and the importance of localized ground-truthing. This approach enhances the capabilities of earth observation for carbon stock assessments and supports informed decision-making in conservation and climate policy. The work also highlights the need for further integration of local knowledge and advanced EO sensor data to refine carbon sequestration models and improve mangrove management strategies.

Seven Years of Monitoring the Development of an Oyster Reef Living Shoreline

The implementation of nature-based solutions (NbS), including living shorelines, to mitigate estuarine habitat loss is increasing at a pace exceeding the evaluation of their long-term success. Constructed oyster reefs (CORs) made of shell, concrete, stone, and other materials are one living shoreline tactic that is widely utilized, yet few studies have been conducted to understand the development of CORs within the context of both physical and ecological parameters over longer time scales (4 + years). A COR-based living shoreline project at the Gandy’s Beach Preserve (GBP) in Delaware Bay, NJ, USA, had dual goals of coastal protection and habitat provisioning, which prompted the development of a goal-driven monitoring framework to track project objectives. Methods were developed to quantify the following multi-disciplinary metrics over 7 years: elevations of CORs, waves (height, period, and direction), shoreline elevations, change in extent of vegetation patches, oyster density and size, nekton richness and community composition, and horseshoe crab impingement. The CORs met most of their habitat provisioning objectives as they were colonized by a multi-generational population of shellfish and created habitat for nekton, while posing negligible hazards to horseshoe crabs. However, none of the coastal protection objectives was fully achieved including material stability, wave attenuation, and sediment elevation increase. Results highlight the value of longer-term monitoring to understand performance and the need to match the scale and type of NbS tactic(s) with both the scale of the landscape and the site-specific hydrodynamic conditions to meet project goals.

Migration as Adaptation? The Falepili Union Between Australia and Tuvalu

ABSTRACTAustralia and Tuvalu recently signed a unique treaty called the Australia‐Tuvalu Falepili Union Treaty, on climate change adaptation, migration, and security. Here we analyze the treaty's migration provision which will enable citizens of Tuvalu to live and work in Australia. We ground our analysis in the state of knowledge about climate change and migration in Tuvalu, explaining the Falepili Union and the ways in which its migration provision may be either a mechanism for adaptation or maladaptation. We then describe a range of policy conditions to maximize the adaptation outcomes for Tuvalu and Tuvaluans. These include measures from the Australian government to support Tuvaluans who migrate as well as the Tuvaluan‐Australians who will be key to their integration, and invest in key sectors in Tuvalu such as coastal protection, ICT, and transport. Cooperation between the Tuvalu and Australian governments will also be needed to help direct remittances into public goods and adaptive technologies and practices, to harness the benefits of skills and training for both economies and to monitor the scheme to ensure it delivers adaptation outcomes to Tuvalu and Tuvaluans. Further policy measures discussed include the selection of people eligible for migration and improved communications about the benefits and risks and governance of the scheme. Most if not all of these will be necessary if the migration provision of the Faleplili Union is to be a mechanism for adaptation.

An experimental study of a rectangular floating breakwater with flexible curtains as wave-dissipating components

In this study, the flexible curtains are attached to the bottom of a rectangular floating breakwater as wave-dissipating components. Through a comprehensive experimental investigation, the wave attenuation, motion responses, and mooring forces of the proposed floating breakwater are examined, with a particular focus on the effects of wave height and the hanging length and porosity of the flexible curtain. Meanwhile, comparative analyses are conducted with the stand-alone rectangular floating breakwater and with attaching one rigid slotted barrier. Our experimental results indicate that one underhanging flexible curtain can augment wave attenuation across all tested wave conditions, which is comparable to the rigid slotted barrier. Furthermore, attaching two flexible curtains contributes to a more significant enhancement for harbor or coastal protection, especially against long waves. This can be attributed to the buffer function of flexible curtains, and the increased added mass induced by the water body confined between them, which increases the natural period of floating breakwaters. Furthermore, the attachment of the flexible curtains significantly suppresses the motion responses of the breakwater, which can alleviate the undesirable strong mooring forces. In general, increasing the length or decreasing the porosity of flexible curtains leads to similar trends in the performance of floating breakwaters. The flexible curtains have been proven to be effective wave-dissipating components for rectangular floating breakwaters.

Rekayasa Teknik Guludan sebagai Upaya Rehabilitasi Ekosistem Mangrove di Ekowisata Pantai Alam Serdang Bahari, Pantai Labu, Sumatera Utara

Abrasion at Alam Serdang Bahari Beach (ASB) is increasingly worrying, causing the reduction of mangrove forests on the coast. ASB Beach is located in Regemuk Village, Labu Beach. The ASB Mangrove Forest Farmers Group (KTHM) has made many efforts to continue to exist morally and materially to survive in the ecotourism industry and is trying to re-green the beaches to minimize the impact of abrasion. The results of a field assessment involving lecturers, village officials, and KTHM ASB obtained a roadmap for a sustainable development village with a solution to prevent prolonged abrasion using the simplest and most economical way through engineered bund techniques to protect mangrove plants and also act as a wave breaker. Implementing this PKM aims to make new efforts to plant mangrove trees as coastal abrasion protection. Implementing activities uses a participatory action research (PAR) approach. KTHM, as the partner, carried out the construction of the bund enclosure, and the PKM team was the drafter and supervisor. The results of the PKM implementation are three plots of bunds in the shape of a ship's bow as an effort to break the beach waves using the Rhizopora sp. propagules collected from mangrove seeds by KTHM ASB. This innovation is still early to assess because it requires ongoing monitoring. It is hoped that this effort will better protect newly planted mangrove plants from fierce waves and abrasion as a joint effort to prevent abrasion on ASB Beach.

Effects of Biochar and Nitrogen Fertilizer Application Ratio on Leaf Physiology and Soil Characteristics of Bambusa tuldoides ‘Swolleninternode’

As one of the main bamboo species in coastal sandy land protection forests, Bambusa tuldoides ‘Swolleninternode’ can effectively improve the structure of forest tree species, increase the diversity of tree species and enhance the protection efficiency. However, research on the cultivation and utilization of B. tuldoides is still relatively scarce. Therefore, in this study, B. tuldoides was used as the research object. By applying biochar and nitrogen fertilizer, the effects of different biochar and nitrogen fertilizer ratios on the physiology and soil characteristics of bamboo were analyzed, and the optimal ratio scheme was identified. The results showed that the ratio of the T5 (A2B2C3) treatment had the best effect on the total chlorophyll, non-structural carbohydrate and nutrient contents of B. tuldoides leaves, and the contents under treatments was generally higher than under the control, CK. The activities of soil invertase, nitrate reductase and nitrite reductase were significantly increased under biochar treatment, and the effects of the T5 treatment were the best. The results of principal component analysis showed that the absolute values of the coefficient of leaf potassium, phosphorus content and soil total nitrogen were larger and more important, and the comprehensive evaluation of the T5 treatment was the highest.

Investigations-based results on the hydrographic conditions with special reference to the tourist bathing areas of the protected Romanian littoral

The aim of the present work is related to the new hydrographic conditions within newly developed coastal areas through coastal protection measures extension. The study also seeks to assess the impact on the touristic bathing areas and its safety. The new bathymetry, induced by the sediment size, together with currents propagation into the bathing areas adjacent to the newly arranged beach areas were subject of Conductivity Temperature and depth profiler (CTD) and Acoustic Doppler Current Profiler (ADCP) measurements in relation to the summer waves regime and sea level variations. Several experiments habitually conducted during the summer period were considered; the experiments are related to the marine hazards associated to the swimming areas, such as seasonal storm-inducing currents and the propagation of the rip currents in the nearshore, but also to the specific marine currents setups around beach protection groins and longitudinal breakwater, the influence of vertical water movements, including up-welling and specific intensifications in the periods with complex stormy waves.

A multi-criteria decision-making model for sustainable selection of coastal protection structures

Although nature-based and hybrid (i.e., a combination of hard and nature-based) solutions provide well-documented benefits to both the environment and people living nearby, they cannot be implemented in all coastal zones. Thus, the selection process of coastal protection structures (CPSs) requires an in-depth and comprehensible assessment with an effective and robust decision-support framework. Existing frameworks in the literature, however, do not focus on the selection of nature-based solutions and environmental and social factors were not considered thoroughly in these frameworks. In this respect, this research aims to develop a decision-support model that guides decision-makers in selecting the most appropriate and sustainable CPSs. The framework was designed in a way that includes a variety of environmental and social factors along with economic and technical aspects. Then, fuzzy AHP and TOPSIS analyses were conducted to determine the relative importance of the selection factors and to select the most appropriate CPS. Factors such as sediment dynamics, geotechnical issues, construction cost, transportation and navigation effects, and technological know-how were among the top-rated factors. TOPSIS analysis results revealed that mangrove forests and artificial reefs were the top two most sustainable CPSs. The proposed framework can minimize the social and environmental impacts of CPSs and expedite the green transition in the coastal environment.

Identification and assessment of the mudflat ecological vulnerability dominated by coastline evolution in Jiangsu

Coastlines have experienced profound alterations due to human disturbances and ocean dynamics against the backdrop of climate change and intensified anthropogenic activities. Significant modifications have occurred within the muddy coastal ecosystem, rendering it extremely susceptible to heightened levels of vulnerability. However, existing studies on coastal eco-environmental vulnerability have often overlooked crucial factors such as coastline erosion and siltation, particularly concerning coastline change. In this study, we assess coastline stability utilizing Landsat remote sensing imagery to investigate the vulnerability of coastal ecology alongside 24 economic and natural parameters, serving as indices for the Coastal Vulnerability Index (CVI) of the coastal eco-environment. Subsequently, we analyze the impact factors to vulnerability and predict trends in coastline change over the next 20 years to propose recommendations for sustainable development to safeguard the coastal eco-environment. Our findings reveal a trend towards coastline stabilization in Jiangsu, with significantly higher stability observed during 2010–2020 compared to 1985–2010. The overall CVI along the Jiangsu coast shows an downward trajectory over the past 15 years, primarily influenced by tidal action and coastal topography and geomorphology. Predictive modeling suggests Jiangsu coastline is bounded by the Sheyang estuary, with the coastline to the north dominated by stabilization and to the south dominated by siltation. Climate change, coupled with intensified human activities and future coastline alterations, may exacerbate vulnerability. Effective protection strategies for coastal ecosystems necessitate a comprehensive understanding of local natural conditions, resource availability, and socioeconomic dynamics. Governmental interventions should focus on reinforcing regulatory frameworks for coastal organism management, implementing coastal protection infrastructure, and enhancing supervision and management protocols for beachfront development, thereby fostering the sustainable management of muddy coastlines.

Marsh restoration in front of seawalls is an economically justified nature-based solution for coastal protection

A marsh-fronted seawall is a hybrid nature-based coastal protection solution because it attenuates wave energy, reduces erosion, and provides ecosystem services. However, we still have a limited understanding of how to quantify the marsh wave attenuation benefits for economic analysis. Here, we incorporate a prediction of wave attenuation that accounts for species-specific morphology and structural stiffness into a 1-D wave model and validate it with field measurements. Our results show that the wave attenuation varies by a factor of two across different vegetation species. Further, we performed a benefit-cost analysis, in which the economic benefits represent the environmental services value and avoided seawall heightening cost that would otherwise be required to deliver the same overtopping rate without vegetation. We applied the model to a real-world, marsh-fronted seawall design at Juniper Cove, Massachusetts. Although the benefit of marsh-fronted seawalls is sensitive to discount rate, they have benefit-cost ratios greater than one, indicating that it is an economically justified nature-based solution. Further, we found that wave attenuation and benefit-cost ratio are more sensitive to water depth than wave height. Our study demonstrates the importance of considering the coastal protection of marshes and economic benefits in one framework.

Resilient Coastal Protection Infrastructures: Probabilistic Sensitivity Analysis of Wave Overtopping Using Gaussian Process Surrogate Models

This paper presents a novel mathematical framework for assessing and predicting the resilience of critical coastal infrastructures against wave overtopping hazards and extreme climatic events. A probabilistic sensitivity analysis model is developed to evaluate the relative influence of hydrodynamic, geomorphological, and structural factors contributing to wave overtopping dynamics. Additionally, a stochastic Gaussian process (GP) model is introduced to predict the mean overtopping discharge from coastal defences. Both the sensitivity analysis and the predictive models are validated using a large homogeneous dataset comprising 163 laboratory and field-scale tests. Statistical evaluations demonstrate the superior performance of the GPs in identifying key parameters driving wave overtopping and predicting mean discharge rates, outperforming existing regression-based formulae. The proposed model offers a robust predictive tool for assessing the performance of critical coastal protection infrastructures under various climate scenarios.

Environmental change and connectivity drive coral reef fish abundance in the Western Indian Ocean

Abstract Worldwide, coral reefs are facing risk from climate change. The Western Indian Ocean (WIO) harbours about 16% of global coral reefs with highly reef-dependent local communities. Coastal protection and food security depend on effective conservation management, which requires understanding species abundances. Here, we explore how fish group distribution and abundance across the WIO, categorized by their trophic function, are explained by oceanographic connectivity, sea surface temperature (SST), and chlorophyll a. We designed a proportional oceanographic connectivity metric describing the relative strength of connectivity between all WIO coral reefs and each survey site. We created statistical models for four trophic groups: grazers and detritivores, herbivorous excavators, corallivores, and primary piscivores across 51 sites in the WIO. We show that SST and chlorophyll a are strong predictors of all trophic fish groups and that the proportional oceanographic connectivity metric improved the model predictions significantly for grazers and detritivores and excavators. For excavators, peak abundances were predicted at medium connectivity, and for grazers and detritivores, at low and medium connectivity, suggesting that larvae dispersal predominates at a local scale. Decision making should include connectivity for efficient conservation area prioritization, for which our proportional oceanographic connectivity metric is a valid and useful parameter.

Coastal communities' perceptions on coastal erosion and the protective role of seagrass meadows in Dar es Salaam, Tanzania

Seagrasses are recognized as a nature-based solution for mitigating coastal erosion. However, knowledge on coastal community perceptions regarding coastal erosion causes, impacts, potential mitigation, and the protective role of seagrass meadows is limited in Tanzania. Using stratified random sampling, 323 resident fishers from the Kinondoni and Kigamboni coastal municipalities of Dar es Salaam, Tanzania, were selected to participate in a questionnaire survey to understanding their perceptions of coastal erosion impacts and the protective role of seagrass meadows. Further insights were obtained through key informant interviews with village leaders, elders, and BMU leaders, as well as through nominal group technique involving various beach user groups, and non-participant observation. The study found that coastal communities are highly aware of the causes, impacts, and mitigation measures of coastal erosion, with a notable 85.1 % of survey respondents identifying increased wave energy as the main cause. Nominal group technique revealed various categories affected by erosion, including social activities, properties, sacred sites, livelihood stability, and future development opportunities. The key functions of seagrass meadows as perceived by respondents, including enhancing the natural beauty of coastal waters (97.8 %), supporting fisheries (94.4 %), and providing coastal protection (87.0 %), which ranked third. Destructive fishing was identified as the primary cause of seagrass degradation, notably more severe in Kinondoni. Based on the findings, this study recommends regular awareness campaigns on seagrass preservation. Policymakers should integrate seagrass preservation into broader coastal management plans, promote sustainable fishing, and engage communities to ensure the long-term protection of seagrass meadows as nature-based coastal protection solution.

Using nature-based solutions to improve coastal resilience

As Nature-Based Solutions (NBS) are implemented more widely, it is essential to be clear in our definition of NBS and understand the performance of the various approaches. In this paper we focus on Coastal NBS which involve using natural features to offer or improve coastal protection while producing additional economic, environmental, and social benefits. We illustrate that there are a broad range of solutions spanning the creation of large expanses of habitats, hybrids of habitats and harder engineered structures, and ecological enhancements of existing infrastructure. The performance of these different approaches varies widely, and not all NBS are low-cost or self-maintaining. In many instances, the capacity for sedimentary habitats to self-maintain will depend on sediment availability, a factor that needs to be considered in the whole life costs of these approaches. The incorporation of habitat components can, however, bring multiple benefits for both nature and people. Implemented correctly, Coastal NBS therefore have the potential to be ‘no regret’ solutions in many locations.