Sustainable management model and ecosystem services of mangroves based on socio-ecological system on the coast of Batu Bara Regency, Indonesia

The coastal areas of Batu Bara Regency, Indonesia, face significant challenges due to the conversion of mangrove ecosystems into ponds and tourist destinations. This transformation not only results in the loss of natural coastal protection but also disrupts hydro-oceanography patterns, necessitating comprehensive management solutions that address ecological, economic, and social aspects. To this end, a research was carried out during June to August 2023 developing an integrated management model for sustainable preservation of mangrove ecosystems in Batu Bara Regency. The research aims to evaluate the economic benefits of mangrove ecosystems, particularly emphasizing on regulating, provisioning, and cultural services. The Analytic Network Process (ANP) method is employed to determine priority management strategies by considering the interrelationships between ecological, economic, social, and institutional factors. The model construction incorporates insights from literature reviews and expert interviews, facilitating the formulation of solutions for various aspects of mangrove ecosystem management. The economic value of mangrove ecosystems is estimated in three districts of Batu Bara Regency, with significant contributions to both provisioning and regulating services. In conclusion, the research underscores the importance of strategies such as mangrove area rehabilitation, ecotourism development, outreach and assistance, and community involvement in ensuring the sustainable management of mangrove ecosystems. These strategies hold the potential to preserve these valuable ecosystems, benefiting the environment and local communities alike.


Introduction.
Mangroves are vital ecosystems that provide socially, economically, and environmentally valuable services (Arifanti et al 2022, Hasani et al 2023, Rahmawaty et al 2023).The significant environmental services include coastal protection against wave erosion (Rumondang et al 2022), windbreaks, filtering of seawater intrusion onto land, absorption of harmful heavy metals, pollutant filtration, microclimate regulation, and carbon storage (Yasir et al 2021, Arifanti et al 2022, Rosalina et al 2023).Mangrove forests also serve as habitats or homes for various marine species, feeding grounds, nurseries for growth, and spawning grounds (Rahmawaty et al 2023).They also play a role as stopover points for the migration of various bird species.One of the largest mangrove forests in the world is in Indonesia, covering approximately 3,489,140.68hectares or 23% of the total global mangrove ecosystem.The condition of Indonesia's mangrove forests is known to be 1,671,140.75hectares (47.89%) in good condition and 1,817,999.93hectares (52.10%) in degraded condition (Rahmadi et al 2020, Song et al 2021, Hasani et al 2023).
Mangrove areas in Indonesia have experienced a decline in mangrove cover (Nugraha et al 2019, Kurniawan et al 2021, Hasani et al 2023).One of the regions that has witnessed a decrease in mangrove extent and density is Batu Bara Regency, Indonesia.The degradation of mangroves in the coastal areas of Batu Bara Regency has occurred sporadically since the 1990s.According to interviews with residents of Batu Bara Regency, this occurred due to changes in land use, including the conversion of mangroves into shrimp farms, tourist areas, settlements, plantations, and agriculture, resulting in the loss of coastal protection.As a result of reclamation and coastal development in Batu Bara Regency, the marine hydrological patterns have changed.Coastal erosion disasters in the coastal areas of Batu Bara Regency began with the deterioration of the mangrove ecosystem.During the past decade, the Mangroves areas were reduced by 31.3% at multiple sites along the coast (Rumondang et al 2023).
One of the reasons for the reduction in mangrove area is the high rate of erosion (Fatimatuzzahroh et al 2018, Rumahorbo et al 2019, Rahmadi et al 2020), which has also led to a further decrease in mangrove extent, with coastal erosion reaching inhabited areas.The coastal erosion occurred in various districts.For instance, in Lima Puluh Pesisir District alone, the coastline shift of average value 16.7 m year −1 and increase of 38.0 m year −1 were observed during the period of 2017 to 2021.Similarly, the erosion also took place in other districts with the average erosion rate of 20.9 m year −1 and increase of 15.0 m year −1 in Talawi District, and 23.4 m year −1 and increase of 20.0 m year −1 in Tanjung Tiram District.The overall data exhibited that the erosion rates reach up to 13 m year −1 in the aforementioned districts in Batu Bara Regency (Rumondang et al 2023).
Based on Landsat satellite imagery, the mangrove ecosystem in Batu Bara Regency had a mangrove area of 2,390.4hectares in 2013, 1,851.4hectares in 2017, and 1,643.3hectares in 2022.Therefore, there has been a 31.3%decrease in mangrove forest area from 2013 to 2022, and the trend of mangrove change along the Batu Bara Regency coast has experienced a decline (Rumondang et al 2022).The reduction in mangrove extent has occurred mainly due to anthropogenic activities include land conversion into residential areas, grouper and shrimp ponds, and plantations, resulting in high levels of erosion and significant changes in the coastal areas of Batu Bara Regency, indicating coastal erosion (Rumondang et al 2022).
Damage to the mangrove ecosystem also occurs due to the conversion of areas into ponds and tourist destinations, leading to the loss of natural coastal protection (Hilmi et al 2022), where winds, sea waves, and currents can easily impact the coastal areas (Nugraha 2018, Sui et al 2020, Rahmandhana et al 2022).Simultaneously, this results in changes in the hydro-oceanography patterns due to reclamation and construction along the coast and surrounding areas.The shift in mangrove function in Batu Bara Regency necessitates proper management and presents challenges in terms of mangrove ecology, economics, and social aspects.Various strategies used to address various mangrove issues are still partial and do not integrate all aspects of mangrove management, especially for the affected local communities.Hence, there is a need for a comprehensive management model for a sustainable mangrove ecosystem in the coastal areas of Batu Bara Regency.It is expected that an integrated management model can be optimally and sustainably managed to provide ecosystem services to the surrounding communities.The novelty of this research lies in finding solutions to the issue of changing natural coastal protection due to the conversion of mangroves into tourist areas and pond areas.

Research sites
The study was conducted from June to August 2023, focusing on three districts: Lima Puluh Pesisir, Talawi, and Tanjung Tiram, located in the Batu Bara Regency, North Sumatra, Indonesia.The selection of these districts was based on the substantial availability of mangrove forests in the regency.The map depicting the study area is presented in figure 1.

Data collection
This research utilizes secondary data obtained from the Central Statistics Agency of Batu Bara Regency and the Department of Marine and Fisheries of Batu Bara Regency, North Sumatra.The data include marine production commodities from the three research areas, including crabs, clams, fish, and shrimps in 2022.The production and benefit value of these commodities were calculated based on the daily commodity catch data (kg), commodity price per kg, average fishermen's income ($), the number of fishermen catching the commodity (which varies for each commodity), and the number of days caught per year (215 days).
Meanwhile, the changes in mangrove area in the three locations were determined using images from the Indonesian Geospatial Information Agency for 2013, Landsat 8 OLI/TIRS Collection 2 Tier 1 Raw Scenes satellite imagery for 2017, and Landsat 9 OLI/TIRS Collection 2 Tier 1 Raw Scenes satellite imagery for 2022.The Google Earth Engine and ArcGIS 10.5 platforms were utilized to acquire and process satellite image data.
The area data of mangrove forest was used to calculate the mangrove forest's capacity as a carbon sequestration and oxygen provider.The carbon sequestration benefit was calculated by multiplying the mangrove area by the carbon accumulation rate of 1.74 tons of carbon/ha/year and then multiplying it by the carbon price of $20.47/ton of carbon (Mandela et al 2020).In addition, the oxygen provision benefit was calculated based on the mangrove area multiplied by the ecosystem's potential to produce oxygen, which is 3.65 m 3 /ha/year (Siregar 2012).The result was then multiplied by the oxygen price, which is $3.94 (the price in Indonesia).
Meanwhile, the wave-breaking benefit was calculated using the coastline length and the cost data for constructing a breakwater or tire wavebreaker.Furthermore, the benefits of mangroves as shelter areas and tourist destinations are also considered as ecosystem benefit values.The shelter benefit was calculated based on its utilization by fishermen, reducing fuel needs by 1 liter/day/person due to mangroves reducing exposure to harsh weather conditions.The tourist destination benefit was calculated based on the number of tourists multiplied by the cost spent per person.
After determining all benefit values, the results are then totaled to obtain the total economic value, which encompasses provisioning services (crabs, clams, fish, and shrimps), regulating services (carbon sequestration, oxygen production, and current and wave mitigation), and cultural services (shelter and tourist sites) of the mangrove ecosystems.Meanwhile, data collection for priority analysis was carried out using a survey instrument consisting of two sets of questionnaires, namely issue priorities and solution priorities.

Data analysis 2.3.1. Elasticity of mangrove ecosystem services
This study calculates the economic benefits of the mangrove ecosystem within the components of ecosystem services, namely: regulating services, provisioning services, and cultural services.However, the calculation of ecosystem service values does not include supporting services.Equation (1) was used to calculate elasticity of mangrove ecosystem services.Elasticity represents the degree of responsiveness or sensitivity of one variable to changes in another.In this context, the temporal scale considered for measuring changes is one year.

Mangrove ecosystem management model
The priority analysis was carried out using the Analytic Network Process (ANP) method, facilitated by the SuperDecisions 2.6 software, to determine management strategies.ANP is a relative measurement theory employed to derive composite priority ratios from individual ratio scales, which gauge the relative influence of interacting elements (Saaty 1999).ANP serves as an extension of the Analytic Hierarchy Process (AHP).This method overcomes the limitations of AHP by accommodating the interrelationships between criteria or alternatives.The stages involved in ANP analysis encompass model construction, model quantification, and synthesis and analysis of results.
The questionnaire developed is based on previous studies and literature reviews, resulting in two sets of questionnaires.The first set focuses on issue priorities, while the second set addresses solution priorities.Both scales encompass four aspects: ecology, economy, institutional, and social.Each aspect consists of four items, making a total of 16 items for each questionnaire.The questions in the questionnaire take the form of pairwise comparison between elements within a cluster.This is intended to identify the dominant influence among elements and the extent of the differences.The scale used includes highest influence (9 or 8), very strong influence (7 or 6), strong influence (5 or 4), moderate influence (3 or 2), and equal influence (1) (Saaty 1999).This study used purposive sampling to choose seven respondents, including the Head of the District Fisheries Office, the Head of the District Forestry Office, Fishery Extension Officers, mangrove activist, and academicians.
The results of the questionnaire were then input into the SuperDecisions software.The subsequent step involves calculating Kendall's coefficient of concordance, a measure of rater agreement that indicates the level of consensus among respondents (R1-Rn) on an issue within a cluster.This coefficient is denoted by W, where 0 < W 1. To compute the value of W, the following steps were taken.The mean value (U) of the total rankings for each cluster was calculated using equation (2).
The sum of squared deviations (S) was computed using equation (3).
The maximum sum of squared deviations (Max S) was determined with equation (4).

MaxS
The value of W in the rater agreement was calculated using equation (5).
If the value of W equals 1, it signifies perfect agreement among respondents.Conversely, if W equals 0 or approaches 0, it indicates disagreement among respondent answers or variability in responses Saaty, Vargas (2006).Note that the completeness of the explanation ensures a clearer understanding of the calculations involved in determining Kendall's coefficient of concordance.

Provisioning services
According to figure 2, fish commodity has the highest value among four commodities reaching up to $162,486,812.06/ha/year in Talawi District, followed by shrimps as the second largest with $2,375,737.25/ha/year in Tanjung Tiram District.In addition, the economic values of crabs and clams exhibit major differences as compared to fish and shrimps.The highest values of both crabs and clams were observed in Talawi District which has been seen to generate a maximum annual income of $63,423.05/ha,while clams earned $190,953.53/ha.Further, the production benefits values of all four commodities were calculated for the years 2013, 2017, and 2022 in each of the three districts to determine if the decline of mangrove areas influenced the values.Figure 3 shows a significant decrease in the mangrove area within the research sites.The largest decrease occurred in Lima Puluh Pesisir District, amounting to 43% from 2013 to 2022.Meanwhile, Talawi and Tanjung Tiram experienced respective decreases of 41% and 34%.
Moreover, based on figure 4, it was observed that the production benefit values of four commodities decreased gradually over the years in each of districts.In Lima Puluh Pesisir District, for instance, fish production decreased over the span of three years, from $12,838,507,744.23 (2013) to $7,822,968,210.07 (2017), and finally to $7, 334,729,848.34 (2022), as mangrove areas decreased.This trend also occurred in two other districts.Similarly, in Tanjung Tiram District, the value of clam production benefits decreased from $41,731,461.12 in 2013 to $30,209,881.05 in 2017 and being dropped to $27,584,895.00 in 2022 as a result of a major decline of mangrove areas from 573.91 ha in 2013 to 379.36 ha in 2022 (figure 3).
Subsequently, the elasticity calculations for all commodities showed a value of 1, indicating unit elasticity.This result showed that changes in the mangrove ecosystem's area will result in a constant change in the ecosystem service benefit as a provider of mangrove crabs, clams, fish, and shrimps.

Carbon sequestration
Mangrove ecosystems have ecologically significant functions, especially in coastal areas.One of the ecological functions of mangroves that is currently being discussed is their role as carbon absorbers and storers.Mangrove  forests have the capacity to store more than three times the average carbon per hectare when compared to terrestrial tropical forests (Donato et al 2012).The value of mangroves ecosystems from three Districts of Lima Puluh Pesisir, Talawi, and Tanjung Tiram were quantified.According to figure 5, the values of mangrove areas as providers of carbon sequestration decreased steadily from 2013 to 2017 to 2022.For instance, the values in Lima Puluh Pesisir District decreased from $ 19,677.63 (2013) to $11,990.30 (2017) and then to $11,241.97 (2022).A comparable pattern was observed in two other districts, where the carbon sequestration value of Talawi's mangrove areas decreased from $7,021.65 in 2013 to $4,156.93 in 2022.Similarly, in Tanjung Tiram District, the value went from $20,440.92 in 2013 to $14,799.10 in 2017, and further decreased to $13,513.30 in 2022.
The elasticity calculation results show a value of 1, indicating elasticity, meaning that changes in mangrove area will result in a constant change in the ecosystem service benefit as a carbon sequestration provider.

Oxygen provider
Another ecosystem regulation service provided by mangroves is oxygen production.In the process of photosynthesis, mangrove plants produce oxygen.Besides being used for respiration, the oxygen generated by mangroves is utilized by microorganisms in the decomposition of organic matter.The benefit of mangroves as oxygen producers is estimated by using the potential oxygen production of mangroves as oxygen producers.The calculations of the mangrove's ecosystems estimated benefit were made in three districts, namely Lima Puluh Pesisir, Talawi, and Tanjung Tiram.Based on the data shown in figure 6, it can be observed that there was a continuous decrease in the value of oxygen providers throughout all three Districts from 2013 to 2017 and projected up to 2022.In addition, figure 5 shows that there was a significant decrease in annual benefit values from 2013 to 2017 in Lima Puluh Pesisir and Tanjung Tiram Districts, with values dropping from $7,948.71/year to $4,843.44/year and $8,257.04/year to $5,978.04/year,respectively.However, Talawi did not undergo a significant decrease, as the value fell from $2,836.37/year in 2013 to $2,408.91/year in 2017.In addition to it, the value demonstrated a constant decline in the three districts from 2017 to 2022.The elasticity calculations show a value of 1, indicating that changes in the mangrove area will result in a constant change in the ecosystem service benefit as oxygen producers.

Current and wave mitigation
Physically, mangrove forests growing in coastal areas can withstand the impact of ocean waves, winds, storms, and even tsunami waves, thus providing protection to coastal communities and preventing beach erosion (Riyandari 2019).In this section, the assessment of the mangrove ecosystem services as a current and wave breaker is done by calculating the cost required for building a breakwater.According to Arifanti et al (2022), the cost of constructing a breakwater is $65,521.70 for a length of 180 m or $364,009/km.
The calculation results for year 2013 in this study show that Lima Puluh Pesisir has the highest value of current and wave breaker which amounted of $219,086.54followed by Tanjung Tiram $213,158.46and Talawi $40,739.75 (see S.I.1).The values are getting higher in line with the increase of coastline length covered by mangroves areas in which Lima Puluh Pesisir was the longest (17.37 km).However, it is necessary to note that the mangrove thickness was excluded during this assessment as it is assumed to have the same impact on its function as a current and wave breaker.Moreover, it is found that the elasticity value is 1, indicating that changes in the area of mangrove ecosystems will result in a constant change in the benefits of the ecosystem service as a current and wave breaker.
Further assessment was carried out by calculating the cost required for building a wavebreaker made of used tires along the coastline of Tanjung Tiram.This district was chosen as mangrove benefit assessment in 2017 and 2022 since the data shown in 2013 indicate the highest among others.In 2017, the value for mangrove ecosystem service as a current and sediment breaker is $3,074.40(S.I.2).The elasticity calculation shows a value of 1, indicating that changes in the area of mangrove ecosystems will result in a constant change in the benefits of the ecosystem service as a current and sediment breaker.
In 2022, the value for service as a current and sediment trap was calculated by estimating the cost required for the construction of a concrete wavebreaker along the Tanjung Tiram coast.The cost of constructing the concrete wavebreaker is $170,811.58per km for five-years economic life of the concrete wavebreaker.The length of the coastline protected by the mangrove ecosystem in the Tanjung Tiram District in 2022 is 23.44 km.Data in S.I.3 show that the value for mangrove ecosystem benefit is $770,736.03/year.The concrete wavebreaker project is still under construction, and the funds used for the concrete wavebreaker project in the Tanjung Tiram District amount to $49,929.54 (for 300 meters).In addition, the elasticity calculation results show a value of 1, indicating elasticity, meaning that changes in the mangrove ecosystem's area will result in a constant change in the ecosystem service benefit as a current and sediment trap.

Shelter area
The mangrove ecosystem is utilized as a shelter for some fishermen who engage in fishing activities.Fishermen choose to take shelter around mangroves while waiting for their fishing gear instead of returning home, citing fuel savings as a reason.The economic value of the mangrove ecosystem as a shelter is approximated through the calculation of the fuel cost savings.It is estimated that fishermen can save an average of 1 liter of fuel per day.As demonstrated in table 1, the value of ecosystem service as a shelter is $ 178,396.28, $237,155.46, and $347,187.69 in Lima Puluh Pesisir, Talawi, and Tanjung Tiram Districts, respectively.However, the extent of shelter does not significantly affect the value of fuel cost savings.This occurred as fishermen accessing mangroves for shelter remain the same even if the fuel cost savings change (Arifanti et al 2022).

Tourist destinations
The beach tourism found on the coast of Lima Puluh Pesisir District is located in Perupuk Village, namely Sejarah Beach.Sejarah Beach also showcases Japanese culture, as according to the story, this coastal area used to be a landing place for Japanese ships.Meanwhile, there is Bali Beach in Talawi District and Galuh Beach in Tanjung Tiram.The calculation of the value of tourism services uses the individual expenditure approach in conducting tourist trips.Expenditures in traveling to tourist destinations consist of consumption costs, transportation costs, and entrance ticket fees incurred in a single visit (Arifanti et al 2022).The estimated value of the mangrove ecosystem as a tourist attraction is obtained by multiplying the cost of travel incurred by tourists by the number of tourists who visit during a specific period.The costs incurred by tourists are same for Lima Puluh and Tanjung Tiram, which is $2.63 per person, while for Talawi is $3.28 per person.Such expenses include entrance fees, food, and beverages.The data of visitors to the beach in each District during 2022 were obtained from Central Statistics Agency (2023).According to table 2, the benefit values in 2022 are $84,764.59(Sejarah Beach), $5,387.13(Bali Beach), and $1,949.88(Galuh Beach).
Two islands namely Salah Namo Island and Pandang Island in Tanjung Tiram Districts were assessed.The estimated value of island tourism is obtained by multiplying the expenses incurred by tourists by the number of tourists visiting.In Salah Namo Island the visitor's expenses are approximately $9.85 per person whereas each person is imposed around $11.83 including boat transportation costs.However, the entrance fee to the islands is free.According to table 2, the value for this ecosystem service is $28,282.46/yearfor Salah Namo Island and $14,190.50/yearfor Pandang Island.3.1.4.Total economic value Economic value is the sum of the values of provisioning services (crabs, clams, fish, and shrimps' provisions), regulating services (carbon sequestration, oxygen production, and current and wave attenuation), and cultural services (shelter and tourist sites) of the mangrove's ecosystems.Table 3 shows total economic value of three districts.
According to table 3, Tanjung Tiram District has the greatest total economic value, followed by Talawi and Lima Puluh Pesisir Districts.Mangrove ecosystem in Tanjung Tiram District generated $33,376,188,996.45for its provisioning service, $1,005,941 for the regulating service, and $391,610.52for the cultural services.The total economic value is $33,377,586,547.82.In addition, the economic value of the mangrove ecosystem in Talawi District showed the value of $19,074,435,523.55 for the provisioning services and the economic value of $46,576 for its regulating service as well as $242,542.60for the cultural services.The total economic value for Talawi District is $19,074,724,642.00.Meanwhile, the economic value of the mangrove ecosystem as a provisioning service in Lima Puluh Pesisir District is $7,603,581,017.25,and as a regulating service is $234,870.In addition, cultural services contribute to the total economic value of the mangrove ecosystem at $263,160.87.Therefore, the total economic value of mangrove ecosystem services on the Lima Puluh Pesisir coast is $7,604,079,047.78.

Management strategies for mangrove ecosystems 3.2.1. Concept of mangrove ecosystem management
The results of the ANP analysis for issue priorities are presented in table 4. It is evident that the primary concern in managing the coastal ecosystem in Batu Bara Regency is land conversion of mangrove areas.The second priority is the lack of synergy among sectors in mangrove ecosystem management policies.The third priority is coastal erosion, and the last is community perception.

Priority solutions for mangrove ecosystem management
The results of the ANP revealing the primary solutions for managing the mangrove ecosystem on the coast of Batu Bara Regency are presented in table 5.The highest-priority solution is the rehabilitation and conservation of the mangrove ecosystem.Following closely, the second priority is the development of eco-tourism.The third priority is focused on outreach and assistance, while the fourth priority involves mangrove management and supervision, with active community engagement.Within the ecological dimension, the leading solution also revolves around the rehabilitation and conservation of the mangrove ecosystem.Rehabilitation, in this context, refers to activities designed to transform a damaged ecosystem into a more balanced and functional alternative.These rehabilitation efforts aim to restore the health of damaged mangroves, thereby enabling the mangrove ecosystem to operate effectively.
Table 6 shows Kendall's coefficient determined using response data from seven respondents to two types of questionnaires, namely the issue and solution priorities questionnaires, totaling 32 items.The Kendall's coefficient value obtained is 0.709.This indicates a moderate to strong level of agreement among respondents in prioritizing issues and solutions for mangrove ecosystem management.

Discussion
The analysis of the elasticity of ecosystem services in this study revealed consistent values of 1 for all types of services.This indicates that changes in the mangrove ecosystem's area will result in a constant change in the ecosystem service.In terms of provisioning services, fish played the most significant role.Regarding the carbon sequestration capacity of mangroves, their ability has declined over the years.For instance, in the case of Lima Puluh Pesisir District (the largest among the study locations), the total carbon sequestration was 96 tons in 2013, decreasing to only 20 tons in 2022.Meanwhile, in oxygen provision, the mangrove ecosystem service also exhibited a decrease.For example, in the case of Tanjung Tiram District, it went from 2.09 ×10 −3 m 3 in 2013 to 1.38 ×10 −3 m 3 .Concerning the economic value of the mangrove ecosystem, the region contributing the most significant economic value was Tanjung Tiram District.In this case, it was not related to coastal length but rather the abundance of fish commodities in the area.The mangrove ecosystem provides ecological benefits as a supplier of nutrients, a spawning and feeding ground for various aquatic species, a protector of coastlines from erosion, a nursery area for many fish and crustacean species, a barrier against seawater intrusion and strong winds, and a wave buffer.Additionally, it offers economic benefits as a source of various wood products, ecosystem services, and provides a habitat for mangrove nursery areas.
The ANP analysis results show that each aspect of the issues has its own priority.In the ecological aspect, the top priority issue is coastal erosion.Coastal erosion can occur naturally due to wave action and can also result from human activities such as mangrove forest clearance, coral harvesting, port construction, and expansion of shrimp farming areas toward the sea (Nugroho et al 2020).The imbalance in coastal sediment balance is primarily a result of sand mining activities by communities along the coastal areas (Sofyan 2014).The main issue that arises in the economic context is land conversion of mangroves.One form of mangrove land conversion involves cutting down its trees and redirecting the area for other potential uses, which may have wide-ranging impacts.While mangrove land conversion can increase community income and job opportunities, it also carries the risk of reducing the mangrove area, leading to ecosystem damage (Rusdianti and Sunito 2012).Further studies by Rahman et al (2020) indicate that mangrove land conversion can result in a reduction in the extent and density of mangrove ecosystems, ultimately affecting the overall structure and status of the mangrove ecosystem.
One contributing factor to mangrove ecosystem damage is the transformation of mangrove land into shrimp farming areas.
The priority issue in the institutional aspect is that the cross-sector policies for mangrove management are still not synergistic.The primary issue in the institutional aspect related to mangrove management is the lack of synergy among various relevant sectors in policy development.Although mangrove management involves sectors such as environment, fisheries, marine affairs, forestry, and agriculture, it is often observed that the objectives and policy measures taken by each sector are not fully aligned.The impact of this issue can be seen in the form of conflicting interests, policy overlaps, and a lack of effectiveness in mangrove conservation and management as a whole.Therefore, it is essential to strive for better coordination among these sectors, prioritize open communication, and design integrated management plans to achieve holistic and sustainable mangrove protection goals.The priority issue in the ecological aspect is coastal erosion.Coastal erosion occurs when natural or human activities result in the removal and release of soil materials from the shore into the sea or water bodies.This erosion is often caused by mangrove deforestation and coastal development, which reduce the natural protection provided by mangrove forests.Without this protection, waves, currents, and winds can damage and carry away coastal soil, endangering coastal ecosystems and human infrastructure.Mangroves play a crucial role in maintaining coastal stability with their strong roots and the food chains within this ecosystem.However, the degradation of the mangrove ecosystem due to human activities such as illegal logging, land reclamation, and pollution can reduce its effectiveness in controlling coastal erosion.Without healthy mangroves, coastal communities become more vulnerable to the adverse effects of coastal erosion, including land loss, homes, and public facilities.Additionally, the marine environment can also be affected, as the sediments carried by seawater can harm coral reefs and other marine life.
Within the social dimension, a key issue that comes to the forefront is the perception of the community.Perception, in a broad sense, is often defined as the manner in which a community or an individual perceives an object, whether it be a physical entity or a social construct (Setiawan 2017).The community's perception of the mangrove ecosystem holds paramount importance as it is closely linked to their attitudes and interactions with mangroves.Communities, being daily users who engage directly with the ecosystem, are expected to possess a solid understanding of the mangrove ecosystem.Consequently, the well-being of the mangrove ecosystem and its ability to provide optimal benefits to the community are contingent on this understanding.A positive perception plays a pivotal role in determining the sustainability of the mangrove ecosystem.
Efforts to rehabilitate the coast can be carried out by restoring the coastal zone's function as a green belt to maintain shoreline stability.The mangrove green belt is crucial for the sustainability of life, especially in coastal areas.The green belt serves several functions, including: (1) a source of primary productivity in the waters, (2) a shelter for organisms, (3) a stabilizer of sediment deposition areas, and (4) a buffer against wind, waves, currents, and pollutants from both land and sea.In other words, the coastal green belt boundary is the part of the mangrove forest that is preserved, bordering the coast or riverbank with its unique natural characteristics that can have vital, physical, and chemical functions for the waters (Soemarno 1986).The optimum and minimum width of the green belt, considering the level of inundation and the average green belt class, ranges from 510 m to 3555 m.The establishment of the green belt should take into account ecological, economic, and social aspects (Zen et al 2012).
The best defense to protect an area from erosion processes is mangrove forests (Bengen 2001).Research by Handayani et al (2020) suggests that mangrove rehabilitation along the coast needs to be continuously carried out to increase the coverage and extent of the mangrove ecosystem, given that the availability of regulation services related to coastal erosion control tends to be in a deficit balance.Coastal mangrove rehabilitation needs to be combined with coastal structures.This is because the oceanographic conditions in the waters of Sayung are relatively strong.Coastal structures or wave breakers, besides reducing currents and waves and trapping sediments, also protect newly planted mangroves from wave impacts.Mangroves that successfully grow and develop will trap mud or fine sediments, expanding the mangrove land and accelerating the formation of soil or sediment deposits.Modeling shows that the current velocity in the waters is quite strong, significant wave heights are relatively high, with a relatively fast period.This is what causes the erosion rate in the waters to increase every year.Effective prevention involves building detached structures like seawalls or revetments or a combination of both to prevent more extensive erosion.Pasaribu et al (2021) added that the existing coastal structures with the highest ability to capture transported sediments in the waters are breakwaters and coastal belts.
In the formulation of a rehabilitation plan, a comprehensive strategy encompassing physical, biological, and social aspects must be employed.The physical approach entails the construction of physical structures aimed at mitigating the impact of strong oceanographic factors.As prior research has highlighted, for enhancing the sustainability of mangrove ecosystem management along the coast, it is imperative to consider oceanographic conditions and implement measures for coastal erosion control within the ecological dimension Chow (2018).The biological approach involves the planting of mangroves as a natural coastal protective barrier.The social approach revolves around increasing community involvement in initiatives related to coastal erosion control and mangrove ecosystem management.This approach is in line with the findings of Surayya et al (2020), who emphasize that the central concept applicable to mangrove ecosystem management and preservation is the safeguarding and restoration of mangrove forests.One effective strategy for preserving the mangrove ecosystem is to designate it as a conservation area or a green belt along the coast.Additionally, Gracia et al (2018) added that utilizing the mangrove ecosystem is one of the strategies for coastal protection based on an adaptive and sustainable ecosystem approach to address coastal erosion.
The top economic solution entails the promotion of mangrove ecotourism.Ecotourism is a concept that leverages natural resources for tourism development while emphasizing conservation (Yulianda 2020).It represents an alternative program that can enhance the well-being of local communities as a proactive measure against potential harm to the mangrove ecosystem (Wardhani 2011).Furthermore, ecotourism initiatives contribute to the dissemination of knowledge and the preservation of biodiversity.Given the essence and principles of ecotourism, its advancement should result in economic and social advantages for the local populace, all the while upholding sustainability.Therefore, according to Wardhani (2011), the feasibility of marketing, technical, financial, environmental, and social aspects in developing mangrove areas for ecotourism should be clearly identified before implementation.
The priority solution in the social aspect is outreach and assistance.Solutions in the social aspect related to mangrove management can be realized through extensive outreach and assistance efforts.Outreach and assistance aim to raise awareness, knowledge, and the involvement of the local community in mangrove conservation and management efforts.Outreach involves providing accurate and easily understandable information to the community about the benefits of the mangrove ecosystem, the negative impacts of activities that harm mangroves, and the importance of each individual's role in preserving them.With effective outreach, communities can better understand the close relationship between their well-being and mangrove sustainability, leading to a collective awareness of taking actions that support its preservation.Assistance involves direct efforts to help communities implement sustainable practices in mangrove management.This can include training in proper mangrove planting techniques, waste management, avoiding overfishing in mangrove areas, and more.With ongoing assistance, communities can feel supported and guided in their role as key actors in preserving the mangrove ecosystem.Outreach and assistance complement each other, where outreach provides the necessary knowledge foundation, while assistance activates communities to apply that knowledge in their daily practices.Furthermore, community involvement in the development of management plans and decision-making is also crucial, as it fosters a sense of ownership and greater responsibility for mangrove sustainability in their environment.
The priority solution in the institutional aspect is the agreement on inter-sectoral policies in mangrove management.Focused on the relevance of generating monitoring for evaluating management, the emphasis shifts towards enhancing address verification measures.Resilient monitoring systems is important in assessing the effectiveness of these measures in the context of the economic importance of ecosystem services for the local economy and challenges related to climate change.To promote collaboration and mitigate potential conflicts, a collaborative forum is essential, involving representatives from diverse sectors such as environment, fisheries, marine, forestry, agriculture, and other stakeholders.This forum works to formulate policies that mutually support one another and consider the equilibrium of the mangrove ecosystem and its benefits across various sectors.The development of inter-sectoral policy agreements requires intensive dialogue, scientific data gathering, and impact analyses to integrate diverse perspectives and prevent conflicts of interest.The implementation of mechanisms for regular monitoring and evaluation is crucial for consistent and effective execution of these agreements.Government, policy institutions, and non-governmental organizations play a pivotal role in facilitating policy formulation and oversight among sectors.

Conclusion
This study's results demonstrate that mangrove ecosystems play a significant role in supporting the regional economy.In this research, the total economic value for each district is shown to be $7, 604,079,047.78; $19,074,724,642.00; and $33,377,586,547.82for Lima Puluh Pesisir, Talawi, and Tanjung Tiram Districts, respectively.These findings clearly indicate that the Tanjung Tiram District has the highest total economic value compared to other areas, even though its coastline length ranks second after the Lima Puluh Pesisir District.This is because the mangrove area in Tanjung Tiram can generate the largest provisioning services.The results of the ANP analysis provide recommendations for effectively managing the mangrove ecosystem in Batu Bara Regency.Priority strategies should focus on: (1) mangrove area rehabilitation and conservation, (2) ecotourism development, (3) outreach and assistance, and (4) mangrove management and supervision involving local communities.These strategies will play a crucial role in preserving and sustaining the valuable mangrove ecosystems in the region while benefiting both the environment and local communities.
of mangrove ecosystem services.ΔS: Change in mangrove stock or area.ΔN: Change in the value of mangrove ecosystem services.NA: Initial value of mangrove ecosystem services.SA: Initial area of mangrove.

Figure 5 .
Figure 5. Value of the mangrove ecosystem as a carbon sequestration and total carbon generated (Exchange rate: 1.00 US$ = Rp.15,221.45).

Figure 6 .
Figure 6.Value of the mangrove ecosystem as an oxygen provider and total oxygen provided (Exchange rate: 1.00 US$ = Rp.15,221.45).

Table 1 .
Economic value of the mangrove ecosystem as shelter.

Table 2 .
Value of the mangrove ecosystem as a tourist attraction of beach in 2022.

Table 3 .
Total economic value of mangrove ecosystem services.

Table 4 .
ANP results on issue priorities.

Table 5 .
ANP results on solution priorities.