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Mangrove menyediakan berbagai jasa ekosistem, salah satunya adalah sebagai penyerap dan penyimpan karbon biru. Perhitungan jumlah simpanan dan serapan karbon di hutan mangrove menjadi penting karena hutan mangrove di Indonesia memiliki simpanan karbon biru tertinggi di dunia. Informasi potensi karbon biru mangrove dapat diperoleh dari kegiatan monitoring mangrove yang dilakukan secara berkala. Dengan lokasi penelitian di Dumai, Riau, studi ini mengestimasi karbon yang disimpan dan diserap oleh pohon mangrove di tepi sungai dan dalam hutan. Struktur komunitas diketahui dengan menghitung Shannon-Wiener Index , sementara biomasa dan potensi simpanan karbon mangrove dihitung dengan persamaan alometrik khusus berdasarkan jenis. Jenis mangrove yang ditemukan di lokasi penelitian antara lain Rhizophora apiculata , Avicennia marina , Xylocarpus granatum , Bruguiera gymnorrhiza , Sonneratia alba , Lumnitzera racemosa, dan Nypa frutican, dimana Stasiun Tepi Sungai didominasi oleh Xylocarpus granatum (kisaran O 1.36-23.25 cm), sementara Rhizophora apiculata mendominasi stasiun di dalam hutan dengan kisaran O 1.27-23.25 cm. Laju pertumbuhan mangrove cukup beragam dan Avicennia marina memiliki laju tercepat. Hasil menunjukan bahwa dengan estimasi rata-rata biomasa mangrove sekitar 596.56 Mg ha -1 hutan mangrove di Dumai, Riau berpotensi menyimpan karbon sebesar 285.24 Mg C ha -1 . Karbon yang tersimpan di Stasiun Dalam Hutan lebih besar (332.9 Mg C ha -1 ) dibandingkan dengan di Stasiun Tepi Sungai (237.58 Mg C ha -1 ). Apabila satu hektar hutan mangrove di Dumai, Riau, rusak atau hilang, maka potensi karbon yang dilepaskan sebesar 1046.83 Mg CO 2 ha -1 , yaitu setara dengan jumlah CO 2 yang terlepas dari pembakaran 524.82 ton batu bara. Mangroves provide various ecosystem services, one of which is as a carbon sink and storage. The assessment of mangrove carbon stock and sequestration becomes a global concern especially for Indonesia’s mangrove forests that store most of mangrove blue carbon in the world. Blue carbon potentialsl in mangroves can be estimated by assessing mangroves through periodic monitoring. Here, the study was undertaken in mangrove forests in Dumai, Riau and aimed to assess the carbon stored and sequestered in mangroves located riverside and inside the forests. The forest structure was examined with the Shannon-Wiener Index, while biomass and potential carbon storage of mangroves calculated by specific allometric equations based on the species. The species found in the study site were Rhizophora apiculata, Avicennia marina, Xylocarpus granatum, Bruguiera gymnorrhiza, Sonneratia alba, Lumnitzera racemosa, and Nypa frutican. The riverside station was dominated by Xylocarpus granatum (ranging O 1.36-23.25 cm), while Rhizophora apiculata dominated the station inside the forest (ranging O o1.27-23.25 cm). The rates of mangrove growth varied among the species, with Avicennia marina as the greatest. Our result showed that the mean of mangrove biomass in the study site was 596.56 Mg ha -1 with carbon stock potential of 285.24 Mg C ha -1 . Mangroves inside the forests stored more carbon (332.9 Mg C ha- 1 ) than ones in the riverside (237.58 Mg C ha- 1 ). We estimated that the destruction of one hectare of mangrove forest in the study site can potentially release 1046.83 CO 2 , which is equivalent to CO 2 released from 524.82 tonnes of burned coals.

There has been a growing interest in restoring mangroves to reduce and offset carbon (C) emissions, but it is still unknown whether restored mangroves provide ‘blue carbon’ services similar to natu...

Mangrove restoration projects are now widely established, aiming to regain the carbon benefit of the mangrove ecosystem that is essential for climate change mitigation. This study aimed to investigate mangrove litter as the source of carbon in restored mangrove forests in Perancak Estuary, Bali, Indonesia, which previously experienced substantial mangrove loss due to shrimp aquaculture development. We assessed the production and decomposition of mangrove litter and associated macrozoobenthic biodiversity in restored forests with plantation age ≥14 years and intact mangrove forests as the reference. The monthly production of three groups of mangrove litter (leaf, reproductive, and wood) was assessed over 12 months. A leaf litter decomposition experiment was performed to inspect the interspecific and disturbance history variation in organic matter formation among four major mangrove species: Rhizophora apiculata, Bruguiera gymnorhiza, Avicennia marina, and Sonneratia alba. Our results showed that annual litterfall production from restored and intact mangroves in Perancak Estuary were 13.96 and 10.18 Mg ha−1 year−1, which is equivalent to approximately 6282 and 4581 kg C ha−1 year−1 of annual litterfall carbon sink, respectively. Although restored mangroves had significantly higher plant litterfall production than intact mangroves, no significant difference was detected in leaf litter decomposition and macrozoobenthic biodiversity between these forest types.

The geomorphology of mangrove ecosystems is strongly influenced by hydrodynamic factors. Mangrove growth is conditional on water and sediment budgets at the coastal interface. This basic ecological principle has been ignored in many mangrove restoration or rehabilitation programs, leading to failures in the design of successful and cost-effective ecosystem restoration and rehabilitation. This chapter highlights how restoring tidal flows can adequately supply sediments to the mangrove system and stimulate its recovery in abandoned aquaculture ponds, where hydrology was previously constrained by pond walls. Tidal flows transport sediments that accumulate in the pond, causing an increase in soil surface elevation; a key factor in both helping minerogenic mangroves maintain their elevation in the face of sea level rise and improving the local blue carbon balance through carbon accumulation. In a number of cases, tidal flow also facilitates the dispersal of mangrove propagules over the site, contributing to subsequent mangrove development. As restoring the hydrological regime is most likely to have positive contributions to the early development of mangroves in abandoned ponds, it should be considered as a “nature-inspired” alternative to plantation programs. Our work suggests that such “passive” mangrove restoration strategies are to be preferred as they provide better opportunities for blue carbon abatement and increase resilience of coasts to rising sea levels and biodiversity loss.

Globally, carbon‐rich mangrove forests are deforested and degraded due to land‐use and land‐cover change (LULCC). The impact of mangrove deforestation on carbon emissions has been reported on a global scale; however, uncertainty remains at subnational scales due to geographical variability and field data limitations. We present an assessment of blue carbon storage at five mangrove sites across West Papua Province, Indonesia, a region that supports 10% of the world's mangrove area. The sites are representative of contrasting hydrogeomorphic settings and also capture change over a 25‐years LULCC chronosequence. Field‐based assessments were conducted across 255 plots covering undisturbed and LULCC‐affected mangroves (0‐, 5‐, 10‐, 15‐ and 25‐year‐old post‐harvest or regenerating forests as well as 15‐year‐old aquaculture ponds). Undisturbed mangroves stored total ecosystem carbon stocks of 182–2,730 (mean ± SD: 1,087 ± 584) Mg C/ha, with the large variation driven by hydrogeomorphic settings. The highest carbon stocks were found in estuarine interior (EI) mangroves, followed by open coast interior, open coast fringe and EI forests. Forest harvesting did not significantly affect soil carbon stocks, despite an elevated dead wood density relative to undisturbed forests, but it did remove nearly all live biomass. Aquaculture conversion removed 60% of soil carbon stock and 85% of live biomass carbon stock, relative to reference sites. By contrast, mangroves left to regenerate for more than 25 years reached the same level of biomass carbon compared to undisturbed forests, with annual biomass accumulation rates of 3.6 ± 1.1 Mg C ha−1 year−1. This study shows that hydrogeomorphic setting controls natural dynamics of mangrove blue carbon stocks, while long‐term land‐use changes affect carbon loss and gain to a substantial degree. Therefore, current land‐based climate policies must incorporate landscape and land‐use characteristics, and their related carbon management consequences, for more effective emissions reduction targets and restoration outcomes., We present blue carbon (C) assessment from 255 plots covering undisturbed and land‐use change‐affected mangroves (0‐, 5‐, 10‐, 15‐ and 25‐year‐old post‐harvest as well as 15‐year‐old aquaculture ponds) across West Papua Province, Indonesia. Undisturbed mangroves stored total ecosystem C‐stocks of 182–2,730 (1,087 ± 584) Mg C/ha, with variation driven by hydrogeomorphic settings. Forest harvesting did not significantly affect soil C‐stocks, despite increased dead wood density, but it removed nearly all live biomass. Aquaculture conversion removed 60% of soil and 85% of live biomass C‐stocks. Mangroves left to regenerate for 25 years reached the same level of biomass carbon compared to undisturbed forests.

There have been efforts to restore and rehabilitate mangrove forests to compensate for their loss or degradation. Approaches for monitoring these efforts are increasingly developed, including assessment of the dynamic changes in restored mangroves using the biophysical tree parameter called Leaf Area Index (LAI). This study aimed to (1) apply a semi-empirical approach to estimate LAI using WorldView-2 imagery, (2) compare the LAI distributions of three different mangrove forest types (natural, mixed, and planted) at the mangrove restoration site in Perancak Estuary, Bali, Indonesia, and (3) evaluate the applicability of LAI as an indicator for monitoring mangrove growth in restoration areas. To achieve these objectives, a high-spatial-resolution WorldView-2 image data (2 m pixel size) and Normalized Difference Vegetation Index (NDVI) were used. A semi-empirical approach was used to correlate field LAI and NDVI values at the corresponding location. The results showed that the best regression function between the two variables was the third-order polynomial (R2 = 0.98). Overall, the estimated LAI values ranged from 0 to 9.56 (mean = 1.87, σ = 0.95, max. Accuracy = 97.6%) and differed between the three mangrove forest types. The comparison revealed that high LAI was associated with planted mangrove forest type where Rhizophora sp. dominated. It indicates that LAI is a useful indicator for assessing mangrove biophysical conditions and, as such, can be used for monitoring mangrove restoration activities and outcomes.

Forest Reference Emission Level (FREL) is one of four required elements for developing countries in implementing REDD+ activities, and serves as a benchmark in assessing REDD+ performance. This study assessed the emission level from mangrove deforestation in Mahakam Delta - East Kalimantan, aiming to enhance the baseline for subnational FREL document. Over the observation period of 1980-2001, conversion of mangrove forest into aquaculture ponds has resulted in a massive mangrove loss, with an estimation of 3,183 hectare/year, or equivalent to the release of 0.46 Tg CO2e/year. If soil pool was also included in the calculation, mangrove deforestation in Mahakam Delta between 1980 and 2001 emitted 2.9 TgCO2e/year. The CO2 emission from aquaculture ponds may couple with mangrove deforestation, which released 52 Gg CO2 /year from the pond floor. After 2001, the rate of mangrove deforestation decreased, allowing mangrove forests to recover with the expansion rate of 1,546 hectare/ year during 2001-2011 or equivalent to the carbon sequestration or removal of 0.67-4.7 TgCO2e/year. The results of the study suggest the way to improve the existing FREL by raising the importance of mangrove as “blue” carbon, with reference of the 2013 IPCC Guideline: Wetland Supplement.

Tropical estuaries may release large amounts of carbon dioxide to the atmosphere, but remain understudied relative to temperate systems. Here, we investigate hydrological drivers of pCO2 along ~22 km of an aquatic continuum from the mountain river to the coastal ocean, including highly modified aquaculture and urban zones (Perancak Estuary, Ijo Gading River, Bali, Indonesia). We report seasonal spatial surveys (n = 8) and stationary time series observations (n = 4 days) during a rain event. Overall, pCO2 ranged from 330 μatm to 12,126 μatm, with the lowest values observed near the estuary mouth and in the river upstream of the urban zone, and the highest values in the upper estuary where radon (222Rn, a natural groundwater tracer) revealed elevated groundwater discharge. Average atmospheric CO2 fluxes in the upper estuary (107.3 mmol m−2 d−1) were ~5-fold greater than in the lower estuary (19.1 mmol m−2 d−1), while the river was a minor atmospheric CO2 sink (−0.2 mmol m−2 d−1). Overall, the estuary was a source of CO2 to the atmosphere with area-weighted emissions of ~67 mmol m−2 d−1. Seasonal spatial surveys revealed strong correlations between antecedent rainfall and pCO2 and 222Rn in the estuary, implying pCO2 responds to delayed groundwater discharge. A detailed 4-day time series covering an episodic flooding event revealed sharp transitions in CO2 drivers, including dilution by rainfall followed by inputs of CO2-enriched groundwater. Groundwater discharge, as traced by radon, explained most of pCO2 variability in dry and wet conditions. Overall, we highlight the importance of seasonal and episodic rainfall and how delayed groundwater seepage may drive CO2 distribution in a highly modified tropical estuary.

Many drivers of mangrove forest loss operate over large scales and are most effectively addressed by policy interventions. However, conflicting or unclear policy objectives exist at multiple tiers of government, resulting in contradictory management decisions. To address this, we considered four approaches that are being used increasingly or could be deployed in Southeast Asia to ensure sustainable livelihoods and biodiversity conservation. First, a stronger incorporation of mangroves into marine protected areas (that currently focus largely on reefs and fisheries) could resolve some policy conflicts and ensure that mangroves do not fall through a policy gap. Second, examples of community and government comanagement exist, but achieving comanagement at scale will be important in reconciling stakeholders and addressing conflicting policy objectives. Third, private-sector initiatives could protect mangroves through existing and novel mechanisms in degraded areas and areas under future threat. Finally, payments for ecosystem services (PES) hold great promise for mangrove conservation, with carbon PES schemes (known as blue carbon) attracting attention. Although barriers remain to the implementation of PES, the potential to implement them at multiple scales exists. Closing the gap between mangrove conservation policies and action is crucial to the improved protection and management of this imperiled coastal ecosystem and to the livelihoods that depend on them.

Global warming is the important issues because is caused by the concentration increase of greenhouse gasses in the atmosphere. Mangrove ecosystem has a function to reduce climate change through carbon sequestration. Estimates of biomass can be done through an approach from the value of vegetation biomass. Allometric equations method is used for calculating biomass values. Remote sensing technology is used for mapping mangrove ecosystems to determine the spatial distribution of mangrove biomass that is WorldView-2 (WV-2) image. Transformation of the vegetation index are Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI) are used to estimate of mangrove forest biomass. The aim of this study is to determine the most accurate vegetation index in estimating the mangrove above-ground biomass (AGB) value. The field biomass data was obtained from mangrove tree diameter at breast height (DBH) measurement. Using the allometric equation, the field AGB can be calculated. A regression analysis between field biomass and WV-2 image pixel value was performed to build regression function to estimate the mangrove AGB. The results of this study show that the SAVI provided higher accuracy for mangrove AGB estimation with R2 of 0.4125 and resulting the AGB value between 1124.81 to 4499.25 kg/m.

In terms of climate change mitigation, mangroves serve as carbon sinks and the loss of mangrove forests can result in significant release of stored carbon. As the country in the world with the largest cover of mangrove forest, Indonesia has global significance in climate change mitigation. About 22% of mangrove forests in Indonesia are preserved in conservation areas and provide 0.82-1.09 PgC hectare of carbon storage. Greater potential for climate change mitigation can be achieved by increasing mangrove conservation areas that keep mangrove forests from their conversion to other land uses. Our finding confirms the importance of mangrove conservation in storing and sequestering carbon. Furthermore, as mangrove forests are associated with a diversity of ecosystem services with multiple beneficiaries, the carbon benefits will enhance the value of mangrove forest in terms of ecological, social, and economic benefits. However, prioritizing carbon benefits through the implementation of mangrove conservation as part of climate change mitigation may be conflicting with socioeconomic issues. Thus, legal frameworks and the participation of stakeholders, especially local communities, are needed to ensure that there is a net reduction in mangrove loss. This article is categorized under: Climate, Ecology, and Conservation > Conservation Strategies

International audience; Revegetation of abandoned aquaculture regions should be a priority for any integrated coastal zone management (ICZM). This paper examines the potential of a matchless time series of 20 very high spatial resolution (VHSR) optical satellite images acquired for mapping trends in the evolution of mangrove forests from 2001 to 2015 in an estuary fragmented into aquaculture ponds. Evolution of mangrove extent was quantified through robust multitemporal analysis based on supervised image classification. Results indicated that mangroves are expanding inside and outside ponds and over pond dykes. However, the yearly expansion rate of vegetation cover greatly varied between replanted ponds. Ground truthing showed that only Rhizophora species had been planted, whereas natural mangroves consist of Avicennia and Sonneratia species. In addition, the dense Rhizophora plantations present very low regeneration capabilities compared with natural mangroves. Time series of VHSR images provide comprehensive and intuitive level of information for the support of ICZM.

Hutan mangrove di kawasan Estuari Perancak, Jembrana awalnya memiliki area yang sangat luas. Namun seiring dengan perkembangan penduduk, dan peningkatan kebutuhan masyarakat, mulailah pengubahan lahan hutan mangrove menjadi tambak yang mengambil hampir lebih dari 50% lahan asli mangrove . Dengan perkembangan zaman, terdapat teknologi penginderaan jauh yang dapat mengawasi persebaran mangrove alami dan yang ditanami menggunakan indeks vegetasi. Indeks vegetasi yang dapat digunakan antara lain NDVI, EVI2, dan SAVI. Dalam penelitian ini, indeks vegetasi tersebut dimasukkan dalam citra satelit ALOS AVNIR-2 untuk mengetahui rentan nilai indeks vegetasi mangrove alami dan yang ditanami di Estuari Perancak, Jembrana-Bali. Lokasi penelitian penelitian ini berada di Estuari Perancak, Jembrana, tepatnya di desa Budeng dan desa Perancak. Estuari Perancak secara geografis terletak antara 8 o 22’ 30” LS sampai 8 o 24’ 18” LS dan 114 o 36’ 18” BT sampai 114 o 38’ 31,2” BT. Metode analisa indeks vegetasi yang digunakan pada penelitian ini adalah NDVI (Normalized Difference Vegetation Index), EVI2 (Enhanced Vegetation Index-2), dan SAVI (Soil Adjusted Vegetation Index). Hasil penelitian ini menunjukkan bahwa citra ALOS AVNIR-2 mampu digunakan dalam menghasilkan data indeks vegetasi dengan algoritma NDVI, EVI2, dan SAVI. Indeks Vegetasi EVI2 menghasilkan keakurasian hubungan yang lebih baik dibandingkan metode NDVI dan SAVI dimana koefisien determinasinya adalah 0,001. Sedangkan yang memiliki keakurasian hubungan yang lebih baik terhadap EVI2 adalah SAVI, dimana koefisien determinannya sebesar 0,987. Total luas area mangrove di Estuari Perancak adalah 114,19 Ha, dengan pembagian mangrove alami seluas 69,04 Ha dan mangrove ditanami seluas 45,15 Ha.

International audience; Mapping zonations of mangrove species (ZMS) is important when assessing the functioning of such specific ecosystems. However, the reproducibility of remote sensing methods for discriminating and mapping mangrove habitats is often overstated due to the lack of temporal observations. Here, we investigated the potential use of temporal series of high-resolution multispectral satellite images to discriminate and map four typical Asian ZMS. This study was based on the analysis of eight images acquired between 2001 and 2014 over the mangrove area of Nusa Lembongan, Bali, Indonesia. Variations between years in the top-of-atmosphere reflectance signatures were examined as functions of the acquisition angles. We also applied maximum likelihood supervised classification to all of the images and determined the variability in the classification errors. We found that the distinction between spectral signatures of ZMS characterized by a close canopy was fairly independent of the season and sensor characteristics. By contrast, the variability in the multispectral signatures of ZMS with open canopies and associated classification errors could be attributed to variability in ground surface scattering. In both cases, sun-viewing geometry could alter the separability between ZMS classes in near-nadir viewing or frontward sun-viewing configurations, thereby explaining why the overall accuracy of ZMS classification might vary from 65% to 80%. Thus, multitemporal analysis is an important stage in the development of robust methods for ZMS mapping. It must be supported by physical-based research aiming to quantify the influences of canopy structure, species composition, ground surface properties, and viewing geometry parameters on ZMS multispectral signatures.

Mangrove is unique vegetation that lives in tidal areas around the tropical and subtropical coasts. It has important physical, biological, and chemical roles for balancing the ecosystem, as well as serving as carbon pool. Therefore, monitoring the mangrove condition is very important step prior to any management and conservation actions in this area. This study aims to map and monitor the condition of restored mangroves in Perancak Estuary, Jembrana, Bali, Indonesia from 2001 to 2015. We used IKONOS-2, WorldView-2 and WorldView-3 image data to map the extent and canopy cover density of mangroves using visual delineation and semi-empirical modelling through Enhanced Vegetation Index (EVI) as a proxy. The results show that there was a significant increase in mangrove extent from 78.08 hectares in 2001 to 122.54 hectares in 2015. In term of mangrove canopy density, the percentage of high and very-high canopy density classes has increased from 32% in 2001 to 57% in 2015. On the other hand, there were slight changes in low and medium canopy density classes during the observation period. Overall, the result figures from both area extent and canopy density indicates the successful implementation of mangrove restoration effort in Perancak Estuary during the last 14 years.

Large quantities of mud from the LUSI (Lumpur Sidoarjo) volcano in northeastern Java have been channeled to the sea causing high rates of sediment delivery to the mouth of the Porong River, which has a cover of natural and planted mangroves. This study investigated how the high rates of sediment delivery affected vertical accretion, surface elevation change and the growth of Avicennia sp., the dominant mangrove species in the region. During our observations in 2010-2011 (4-5years after the initial volcanic eruption), very high rates of sedimentation in the forests at the mouth of the river gave rise to high vertical accretion of over 10cmy(-1). The high sedimentation rates not only resulted in reduced growth of Avicennia sp. mangrove trees at the two study sites at the Porong River mouth, but also gave rise to high soil surface elevation gains.

There is a need to document how fast mangrove coasts are changing. Within the framework of the INDESO project, we are implementing methods for monitoring changes in Indonesian mangroves over the past decade. The Perancak river estuary, Jembrana, Bali was selected as a pilot site to analyze the impact of aquaculture and plantation practices in a 7 km² mangrove area. During the 80's, most of the mangrove forest was converted to shrimp ponds. However many of shrimp ponds have been abandoned since the 90's and covered by mangroves through plantation programs. We based our analysis on a temporal series of VHR satellite images acquired from 2001 to 2014 aiming to assess the vegetation change over 13 years in the study site. We mapped and quantified the trends of evolution in mangroves in terms of surface extents, forest types and forest structure (young, adult, mature). Our results showed that the Perancak estuary is undergoing the greening, i.e. increasing extent and continuous growing of mangroves. With this approach, we proved that both sustainable and unsustainable coastal zone management practices such as mangrove deforestation, plantation or protection, can be identified and mapped from VHR satellite images.

Sustainable management of mangroves depends on our ability to maintain ecosystem functions. It requires a careful monitoring of several forest characteristics such as the species composition. Very high resolution multispectral satellite images provide pivotal information at the individual tree scale that may support identification and mapping of species of mangrove trees emerging at the canopy level. In this study, we showed that fine scale spectral responses of four common Asian mangroves species were and remained distinct over one decade and, independently of both the satellite sensors and the angular configurations of image acquisitions. We began an important radiative transfer modeling work to interpretation such promising observations.

Many drivers of mangrove forest loss operate over large scales and are most effectively addressed by policy interventions. However, conflicting or unclear policy objectives exist at multiple tiers of government, resulting in contradictory management decisions. To address this, we considered four approaches that are being used increasingly or could be deployed in Southeast Asia to ensure sustainable livelihoods and biodiversity conservation. First, a stronger incorporation of mangroves into marine protected areas (that currently focus largely on reefs and fisheries) could resolve some policy conflicts and ensure that mangroves do not fall through a policy gap. Second, examples of community and government comanagement exist, but achieving comanagement at scale will be important in reconciling stakeholders and addressing conflicting policy objectives. Third, private-sector initiatives could protect mangroves through existing and novel mechanisms in degraded areas and areas under future threat. Finally, payments for ecosystem services (PES) hold great promise for mangrove conservation, with carbon PES schemes (known as blue carbon) attracting attention. Although barriers remain to the implementation of PES, the potential to implement them at multiple scales exists. Closing the gap between mangrove conservation policies and action is crucial to the improved protection and management of this imperiled coastal ecosystem and to the livelihoods that depend on them.

Sea-level rise can threaten the long-term sustainability of coastal communities and valuable ecosystems such as coral reefs, salt marshes and mangroves. Mangrove forests have the capacity to keep pace with sea-level rise and to avoid inundation through vertical accretion of sediments, which allows them to maintain wetland soil elevations suitable for plant growth. The Indo-Pacific region holds most of the world's mangrove forests, but sediment delivery in this region is declining, owing to anthropogenic activities such as damming of rivers. This decline is of particular concern because the Indo-Pacific region is expected to have variable, but high, rates of future sea-level rise. Here we analyse recent trends in mangrove surface elevation changes across the Indo-Pacific region using data from a network of surface elevation table instruments. We find that sediment availability can enable mangrove forests to maintain rates of soil-surface elevation gain that match or exceed that of sea-level rise, but for 69 per cent of our study sites the current rate of sea-level rise exceeded the soil surface elevation gain. We also present a model based on our field data, which suggests that mangrove forests at sites with low tidal range and low sediment supply could be submerged as early as 2070.

Mangroves, the woody halophytes that grow along tropical and subtropical coasts, are key ecosystems that provide important ecosystem services including nursery grounds for fisheries species, habitat for fauna, provision of coastal protection and carbon storage. The distribution and development of mangrove forests reflect their physiological responses to variation in both their biophysical environment and to geomorphological conditions on the coasts. Mangrove forests are under high levels of pressure from human activities in the coastal zone, particularly due to aquaculture, due to changes in sediment delivery to coasts and also due to sea level rise and other factors associated with climate change. Mangrove responses to variation in sediment supply and sea level change as well as to human use of the coastal zone will determine the fate of forests and their capacity to provide ecosystem services. This thesis explores the response of mangroves to human interventions on the coast of Indonesia, with a focus on the effects of altered geomorphological processes and mangrove conversion to aquaculture ponds and the study of restoration after aquaculture on mangrove adaptation to sea level rise and the provision of carbon sequestration services. In the first chapter, I present an assessment of the impact of excessive sediment supply to mangrove forests in Porong, East Java. The next chapter describes carbon emissions associated with conversion of mangrove to shrimp ponds in Perancak, Bali (published as Sidik and Lovelock 2013). The study of mangrove ecosystems after restoration is presented in chapters 4 and 5. I provide an estimation of adaptive response to sea level rise and provision of carbon sequestration services of restored mangrove forests and natural mangrove forests as the natural reference. My research was undertaken in two different mangrove ecosystems in Java and Bali, Indonesia. Indonesia has the world’s largest mangrove coverage of the total global mangrove area, however Indonesian mangroves are facing a high degree of disturbances, for example high sedimentation and mangrove conversion to aquaculture ponds. In Chapter 2, my study revealed that extremely high sediment supply in Porong, due to sediment derived from the LUSI mud volcano, has influenced wetland formation, shown by a strong positive relationship between increase in surface elevation change, measured with rod surface elevation tables, and vertical accretion. Surface elevation gain far exceeded that of local sea level rise and enables mangrove forests to keep pace with sea level rise as well as extending the habitat seaward. On the other hand, high sediment supply had adverse effects on the growth of Avicennia sp. trees. However, field observations found that the mangroves were able to withstand sedimentation rates that exceed tolerances published in the literature. My study on the implication of clearing of mangrove forests for aquaculture (Chapter 3) showed that CO2 released from working shrimp ponds is comparable to other land use conversions in the this region. CO2 released from the wall of working shrimp ponds was higher than from the floors of ponds, demonstrating that the type of habitat modification influences CO2 emissions after disturbance of mangrove forests. In response to extensive mangrove loss, there is new interest in restoring mangrove forests that aims at restoring their ecosystem functions. However, the capacity of restored forests in abandoned aquaculture ponds to rebound to their original state is poorly understood. A study of sediment surface elevation processes in restored and natural mangrove forests in Perancak, Bali (Chapter 4) indicated that surface elevation in restored forests increased at similar rate to that in natural forests. Restored and natural forests were keeping pace with sea level rise as their rates of surface elevation increase were higher than rates of current and projected sea level rise. Surface elevation in both restored and natural forests increased over the time with a strong seasonal pattern, indicating the importance of different processes in the wet and dry season in maintaining surface elevation trajectories. In addition, mangrove root production contributed to surface elevation change with root production tending to be higher in restored forests than in the natural forests, suggesting that restored mangroves undergo strong vegetative growth belowground. In Chapter 5, where I studied the restoration of productivity of carbon sequestration services, revealed the recovery in net primary productivity (NPP) and the carbon sequestration capacity in restored forests. NPP in restored forests was similar to adjacent natural forests and NPP in both sites was relatively high in comparison with values reported in the literature. The total ecosystem carbon stocks in Perancak were low compared to other values reported in the literature for mangrove forests in the tropics. Restored forests had lower carbon stocks but similar rates of carbon sequestration compared to natural forests. The source of carbon in mangrove sediments, as indicated by natural stable isotopes of carbon was dominated by mangrove material. Overall, my study supports the view that mangrove forests are highly productive ecosystems that have a strong capacity to withstand and recover from disturbances and environmental change. Management actions that increase primary productivity of mangrove forests will contribute to the capacity of these forests to keep pace with sea level rise and will have a positive impact on provision of mangrove carbon sequestration. The results of my study provide valuable information to support valuation of ecosystem services provided by mangrove forests and to improve coastal restoration and management plans for sustaining mangrove forests in Indonesia in the future.

International audience; We conducted a literature review to determine the state of the art of hydro- and sediment dynamics modeling studies. We start with a brief overview about mangrove ecosystems while showing various aspects of hydro- and sediment dynamics without claiming exhaustiveness. Since mangrove structures are commonly mimicked using cylindrical stems, papers presenting flow and sedimentation patterns around cylinders are also included in this chapter. We report a significant gap of knowledge of hydrodynamics and sediment transport around mangrove structures at small spatial scales of root systems or trees, single roots or seedlings, and surface texture. To date, most studies are based on field measurements investigating sediment transport around mangrove structures, followed by investigations using flume experiments or numerical simulations. However, Computational Fluid Dynamics appears to be a method with great potential to quantify small-scale dynamics around mangrove structures and could lead to a better understanding of these ecosystems and their processes.

International audience; Coastal instability is not tantamount to vulnerability of mangroves everywhere but rather brings out their exceptional ecological adaptability to cope with morphosedimentary processes. This adaptability has, however, not yet been sufficiently assessed regarding its ability to provide early warning of severe risks induced by marine erosional processes for settlements built backshore of the mangroves. Here we show, using a 68-year (1950–2017) archive of aerial photographs and satellite images, how the monitoring of the fluctuations of mangrove shorelines over the last seven decades may support predictions of coastal vulnerability to erosion in French Guiana. For this example, a coastal vulnerability index of the inhabited shoreline, expressed in years, was developed from the archive of mangrove shorelines and based on estimates of annual erosion rates for each kilometer. This simple mangrove-based early-warning approach is discussed with regards to enhanced observational and modeling considerations of oceanic forcing and sediment processes and oceanic forcing typical of ocean-facing mangrove coasts.

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