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Soil salinity plays an essential role in the growth of mangroves. Mangroves usually grow in intertidal zones. However, in Karimunjawa National Park (KNP), Indonesia, mangroves are also found in supratidal zones. Thus, this study aims to determine why mangroves can grow in this supratidal zone, even during the dry season. We analyze seasonal changes in groundwater flow and salinity dynamics using the hydraulic head, shallow groundwater salinity, and electrical resistivity imaging (ERI) data. The result shows that variation in groundwater salinity is caused by seawater intrusion, which is generated by a hydraulic gradient due to the sea level being higher than the water table in KNP. Rainfall and evapotranspiration, which change seasonally, likely affect the water table fluctuation and salt concentration. ERI images indicate this seawater intrusion in the top sediment up to the bedrock boundary. However, the resistivity difference in the wet and dry seasons shows that remarkable resistivity change occurs at the deeper layer (50–60 m below ground level (BGL)), likely due to freshwater recharge from rainwater on the land side. Groundwater in the KNP is shallow and saline; thus, mangroves in this zone, e.g., Ceriops tagal and Lumnitzera racemosa, can grow because their roots can reach this groundwater. These mangrove species can still grow in this zone even though the shallow groundwater is very saline (46–50 ppt). However, this condition might cause these mangroves to grow stunted. Thus, freshwater availability is crucial for mangrove growth in this supratidal zone to dilute this high groundwater salinity.

Mangroves, a coastal wetland ecosystem with complex above-ground root systems, are known to modulate flow and sediment transport and promote sedimentation – processes that could drive the long-term geomorphic evolution of mangrove forests. However, insights on how and to what extent mangrove forests impact the sedimentary processes and evolution of landscapes and their adjacent areas are limited. This study aims to address these challenges by using a hydrodynamic-sediment transport model and contribute to understanding the effective restoration and management of mangrove forests under the impact of climate change effects such as sea-level rise. A new model was developed to represent the impacts of species-specific three-dimensional root structures (e.g., “prop roots” of Rhizophora species and “pencil roots” of Avicennia and Sonneratia species) on flow and sediment transport and implemented in a hydrodynamic-sediment transport model. This model was applied to a restored estuarine mangrove forest in the Philippines influenced by tidal and fluvial processes. The results show the significant impacts of mangroves on the sedimentation of fluvially-transported sediments in the mangrove forest and nearby areas, which contributed to the areal expansion of the mangrove forest. In addition, due to the increased hydraulic resistance of the mangrove forest following restoration, significant amounts of river flow and sediment discharge are diverted to the other tributary, decreasing the sediment supply downstream of the mangrove forest, a phenomenon that could possibly explain the trend in sediment loss in the area. These results suggest the significance of mangrove forests in driving landscape evolution, not only within the mangrove forest itself but also in adjacent areas, highlighting the importance of considering these areas as a connected system for the management and restoration of mangrove forests.

Among the many ecosystem services provided by mangroves, the sequestration of large amounts of organic carbon (OC) in marine ecosystems (also known as “blue carbon”) has given these unique ecological environments enormous global attention. While there are many studies on the blue carbon potential of intact mangroves (i.e., naturally growing), there have been very few studies on restored mangroves (i.e., planted). This study aims to address this knowledge gap by examining the sediment development process during the early colonization (rehabilitation) of mangroves in an OC-poor estuary in Panay Island, Philippines. Based on source apportionment of multiple end-members in the sedimentary organic matter, the contribution of mangrove plant material was higher at the older sites compared to the younger sites or bare sediments where there is a higher contribution of riverine input. A clear increasing gradient according to mangrove development was observed for bulk OC (0.06–3.4 µmol g−1), porewater OC (292–2150 µmol L−1), sedimentary OC stocks (3.13–77.4 Mg C ha−1), and OC loading per surface area (7–223 µmol m−2). The estimated carbon accumulation rates (6–33 mol m−2 yr−1) based on chronosequence are within the global ranges and show an increasing pattern with the age of mangroves. Hence, the sediments of relatively young mangrove forests appear to be a significant potential C sink, and short-term chronosequence-based observations can efficiently define the importance of mangrove restoration programs as a potential carbon sequestration pathway.

In mangrove forests, soil salinity is one of the most significant environmental factors determining mangrove forest distribution and productivity as it limits plant water uptake and carbon gain. However, salinity control on mangrove productivity through plant hydraulics has not been investigated by existing mangrove models. Thus, we present a new individual-based model linked with plant hydraulics to incorporate physiological characterization of mangrove growth under salt stress. Plant hydraulics was associated with mangroves nutrient uptake and biomass allocation apart from water flux and carbon gain. The developed model was performed for two-coexisting species of Rhizophora stylosa and Bruguiera gymnorrhiza in a subtropical mangrove forest in Japan. The model predicted that the productivity of both species was affected by soil salinity through downregulation of stomatal conductance, while B. gymnorrhiza trees grow faster and suppress the growth of R. stylosa trees by shading that resulted in a B. gymnorrhiza-dominated forest under low soil salinity conditions (B. gymnorrhiza compared to R. stylosa, leading to an increase in biomass of R. stylosa despite the enhanced salt stress (> 30 ‰). These predicted patterns in forest structures across soil salinity gradient remarkably agreed with field data, highlighting the control of salinity on productivity and tree competition as factors that shape the mangrove forest structures. The model reproducibility of forest structures was also supported by the predicted self-thinning processes, which likewise agreed with field data. In addition, the mangroves morphological adjustment to increasing soil salinity – by decreasing transpiration and increasing hydraulic conductance – was reasonably predicted. Aside from the soil salinity, seasonal dynamics in atmospheric variables (solar radiation and temperature) was highlighted as factors influencing mangrove productivity in a subtropical region. The physiological principle-based improved model has the potential to be extended to other mangrove forests in various environmental settings, thus contributing to a better understanding of mangrove dynamics under future global climate change.

In hydrodynamic models, vegetation is commonly approximated as an array of vertical cylinders to represent its impacts on flow and sediment transport. However, this simple approximation may not be valid in the case of Rhizophora mangroves that have complicated three-dimensional root structures. Here, we present a new model to represent the impacts of Rhizophora mangroves on flow and sediment transport in hydrodynamic models. The model explicitly accounts for the effects of the three-dimensional root structures on flow and turbulence, as well as the effects of two different length scales of vegetation-generated turbulence characterized by stem diameter and root diameter. The model employs an empirical model for the Rhizophora root structures that can be applied using basic vegetation parameters (mean stem diameter and tree density), without rigorous measurements of the root structures. We showed that compared to the conventional approximation using an array of cylinders, the new model significantly improves the predictability of velocity, turbulent kinetic energy, and bed shear stress measured in a model and a real Rhizophora mangrove forest. The model further suggested the high efficiency of the three-dimensional root structures of Rhizophora mangroves on sedimentation, which allows a relatively high sediment supply to the forest but effectively regulates sediment erosion through reduced bed shear stress, compared to cylinder arrays that exhibit equivalent sediment supply or sediment retention. The presented model could be a fundamental tool to advance our understanding of the sedimentary processes in Rhizophora mangrove forests which are linked to mangroves’ vulnerability and ecosystem service.

The lack of long–term observational data has limited research on sea–air CO2 exchange variabilities in the Tropical Maritime Continent (TMC). To address the issue, we utilized a three–dimensional high–resolution physical–biogeochemical ocean numerical model and applied it to simulate sea–air CO2 exchange in the region over the last decade (2010–2019). Some key features like atmospheric CO2 source signature and high sea surface pCO2 environment inside the TMC were captured by the model. Within the TMC, model results indicated strong CO2 degassing along the south of Java associated with the seasonal cycle of the upwelling system. Abundant supply of inorganic carbon during upwelling season and strong wind speed results in CO2 degassing that could reach as high as 30 gC m–2 year–1 around the area. In addition to the region acting as a full–year atmospheric CO2 source, the TMC also exhibited interannual modulation in both sea–air CO2 flux and sea surface pCO2 which can be related to the El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Large–scale anomalous strong CO2 degassing and high sea surface pCO2 from 2015 to 2016 in response to the 2015/2016 El Niño evolution was observed and dominated by modulation within the TMC. It is further found that modulation of CO2 degassing related to IOD were confined along the west of south of Java with a higher magnitude compared with anomalies related to ENSO which shows larger spatial scale but lower in the magnitude. Study conducted here may provide insight about possible variabilities of sea–air CO2 exchange in the area that still poorly represented in many global–scale modelling and reconstruction efforts.

The physical, chemical, and biological dynamics under changing atmospheric conditions of Laguna Lake, Philippines were analyzed from intensive observations. Diel measurements were conducted for 48 continuous hours for both dry and wet tropical seasons in addition to fine resolution long-term monitoring. Results revealed significant vertical and diel variations of lake variables in spite of a shallow water depth (2.5 m) caused by the intense surface heating from solar irradiance (~800 W m−2) and accentuated by the lake's high turbidity (16–32 ftu). Late afternoon land-lake breeze (~5–7 m s−1) regularly breaks daytime thermal stratification, and convective cooling at night maintains isothermal condition until dawn of the next day. The stratified condition demonstrated a wind-driven, density-induced 2-layer current pattern with a windward moving epilimnion (~4 folds faster) and a compensating hypolimnetic flow in the general lake circulation direction. Laguna Lake was observed to have a dominating diel cycle but also undergoes significant seasonal limnological variations brought primarily by climate, hydrology, and its interaction with the adjacent sea. Significantly correlated variations of pH, chlorophyll-a and DO in the dry season were indicative of the higher biological activity associated with the intrusion of polluted waters from Metro Manila. The non-occurrence of thermal over-turn was observed to be regularly followed by bottom hypoxic conditions (2–4 mg L−1), indicative of the eutrophic condition of the lake and the importance of diel wind-induced mixing in the bottom supply of DO. Laguna Lake was found to be predominantly net heterotrophic (GPP:R

Many marine species have a pelagic larval phase that undergo dispersal among habitats. Studies on marine larval dispersal have revealed a large variation in the spatial scale of dispersal, and accumulated evidence has shown that seascape patchiness is the major determinant for variation in self-recruitment. However, few studies have investigated the influence of geographic settings on marine larval dispersal. Bays or lagoons generally enhance the retention of larvae, while larvae are more likely to be flushed by strong currents in open coasts. To examine associations between larval dispersal, geographic setting, and hydrodynamics, we compared fin-scale dispersal patterns, self-recruitment, and local retention of two anemonefishes (Amphiprion frenatus and A. perideraion) between a semi-enclosed bay and an open coast in the Philippines combining genetic parentage analysis and biophysical dispersal modelling. Contrary to our expectations, parentage analysis revealed lower estimates of self-recruitment in the semi-closed bay (0–2%) than in the open coast (14–15%). The result was consistent with dispersal simulations predicting lower local retention and self-recruitment in the former (0.4% and 19%) than in the latter (2.9% and 38%). Dispersal modelling also showed that cross-shore currents toward offshore were much stronger around the semi-closed bay and were negatively correlated with local retention and self-recruitment. These results suggest that stronger cross-shore currents around the semi-closed bay transport anemonefish larvae to the offshore and mainly contributed to the lower self-recruitment. Our results highlight difficulty in predicting self-recruitment from geographic setting alone and importance of hydrodynamics on it.

Advancement in Remote Sensing allows rapid mangrove mapping without the need for data-intensive methodologies, complex classifiers, and skill-dependent classification techniques. This study proposes a new index, the Mangrove Vegetation Index (MVI), to rapidly and accurately map mangroves extent from remotely-sensed imageries. The MVI utilizes three Sentinel-2 bands green, Near Infrared (NIR) and Shortwave Infrared (SWIR) in the form |NIR-Green|/|SWIR-Green| to discriminate the distinct greenness and moisture of mangroves from terrestrial vegetation and other land cover. Spectral band analysis shows that the |NIR-Green| part of MVI captures the differences of greenness between mangrove forests and terrestrial vegetation. The |SWIR-Green| part of the index expresses the distinct moisture of mangroves without the need for additional intertidal data and water indices. The MVI value increases with the increasing probability of a pixel being classified as mangroves. Eleven mangrove forests in the Philippines and one mangrove park in Japan were then mapped using MVI. Accuracy assessment was done using field inventory data and high-resolution drone orthophotos. MVI have successfully separated the mangroves from other cover especially terrestrial vegetation, with an overall index accuracy of 92%. The MVI was applied to Landsat 8 images using the equivalent bands to test the universality of the index. Comparable MVI mangrove maps were produced between Sentinel-2 and Landsat images, with an optimal minimum threshold of 4.5 and 4.6, respectively. MVI can effectively highlight the greenness and moisture information in mangroves as reflected by its moderate to high correlation value (r = 0.63 and 0.84, α = 0.05) with the Sentinel-derived chlorophyll-a (Ca) and canopy water (Cw) biophysical products. This study developed and implemented two automated platforms: an offline IDL-based ‘MVI Mapper’ and an online Google Earth Engine-based MVI mapping interface. The MVI implemented in Google Earth Engine was used in generating the latest mangrove extent map of the Philippines. Additionally, the application of MVI were tested to four additional mangrove forests in Southeast Asia: Thailand, Vietnam, Indonesia and Cambodia; and to selected mangroves forests in South America, Africa and Australia.

Among many ecosystem services, macro-climate regulation via the storage of large amounts of organic carbon (OC) in marine sediments (also known as ‘blue carbon’) has given mangroves enormous global attention due to their role in climate change mitigation. While there are many studies on blue carbon potential of intact mangroves (i.e. naturally growing), there have been very few on restored mangroves (i.e. planted). This study aims to address this knowledge gap by examining sediment development process during early colonization (rehabilitation) of mangroves in an OC-poor estuary in the Panay Island, Philippines. Based on endmember source apportionment in sedimentary organic matter, the contribution of mangrove plant material was higher at the older sites compared to the younger settings or bare sediment where there is more contribution of riverine input. A clear increasing gradient according to mangrove development was observed for bulk OC (0.06 to 3.4 µmol g−1), porewater OC (292 to 2150 µmol L−1), sedimentary OC stock (3.13 to 77.4 Mg C ha−1) and OC loading per surface area (7 to 223 µmol m−2). The estimate of carbon accumulation rates (6 to 33 mol m−2 yr−1) based on chrono-sequence are within the global ranges and show an increasing pattern with mangrove age. Although a differential yet systematic pattern of increasing OC sink based on short-term chrono-sequence can define the role of a mangrove rehabilitation program, there is a need for long-term monitoring to verify the consistently elevated OC with mangrove growth.

Blue carbon ecosystems in the Karimunjawa Islands may play a vital role in absorbing and storing the releasing carbon from the Java Sea. The present study investigated mangrove above-ground biomass (AGB) and carbon stock in the Karimunjawa-Kemujan Islands, the largest mangrove area in the Karimunjawa Islands. Taking the aerial photos from an Unmanned Aerial Vehicle combined with Global Navigation Satellite System (GNSS) measurements, we generated Digital Surface Model (DSM) and Digital Terrain Model (DTM) with high accuracy. We calculated mangrove canopy height by subtracting DSM from DTM and then converted it into Lorey’s height. The highest mangrove canopy is located along the coastline facing the sea, ranging from 8 m to 15 m. Stunted mangroves 1 m to 8 m in height are detected mainly in the inner areas. AGBs were calculated using an allometric equation destined for the Southeast and East Asia region. Above-ground carbon biomass is half of AGB. The AGB and carbon biomass of mangroves in the Karimunjawa-Kemujan Islands range from 8 Mg/ha to 328 Mg/ha, and from 4 MgC/ha to 164 MgC/ha, respectively. With a total area of 238.98 ha, the potential above-ground carbon stored in the study area is estimated as 16,555.46 Mg.

Ecosystem services (ES) are benefits nature provides to humans; these services change in space and time and are largely dependent on context. Coastal habitat that provides key ES are blue carbon habitat, namely seagrass and mangroves. One important ES they provide is the provisioning of seafood, which benefits coastal populations with livelihoods and food security. What is the value to society of seagrass and mangrove provisioning ES? What is the spatial reach and variability of these provisioning ES? We employed a social-ecological approach that draws from the vulnerability literature for social, ecological, and economic criteria to map ES provision in ten communities on Busuanga Island, Palawan Province, Philippines. Second, we assess the spatial dynamics of ES provision for small-scale fisheries in seagrass and mangroves, in relation to local beneficiaries. Using a mixed-methods approach with ecological assessments of seagrass beds, spatial analysis, landing surveys, household and key informant interviews, we overlaid biophysical variables on social data, mapping sensitivities and adaptive capacities to compare communities’ vulnerabilities. Spatial analysis revealed healthy blue carbon ecosystems in ten local communities (barangays), as measured by proportion of coastline covered, low patchiness and high continuity along the coastline, and the presence of adjacent habitat. We found seagrass ecosystems were more vulnerable than mangroves. Rural barangays had less exposure and lower sensitivity to blue carbon loss than urban barangays. Blue carbon fisheries are highly sensitive fisheries, due to their catch composition and low catch per unit effort, with mangrove fisheries having a slightly lower sensitivity than seagrass fisheries due to greater catch per unit effort. Diversified livelihoods and the presence of NGOs and People’s Organizations (POs) increased adaptive capacity. We aim to highlight a coastal human community’s relationship with blue carbon resources, using context-specific vulnerability criteria. Our site-specific vulnerability assessment may be adapted for use in other coastal communities within the coral triangle. This work suggests opportunities for conservation interventions to manage local communities’ sensitivities and adaptive capacity around the use of blue carbon resources.

Seagrasses are marine flowering plants which are part of a highly productive coastal ecosystem and play key roles in the coastal processes. Unfortunately, they are declining in area coverage globally, and seagrass losses can be attributed to climate change such as sea-level rise, increase in sea surface temperature, and decrease in salinity, as well as human-related activities. The objective of this research is to assess the historical changes in the seagrass habitat and environment of Busuanga, Philippines using time series data available in the Google Earth Engine (GEE) platform. These include satellite data such as MODIS, Landsat 5, 7, and 8, and SeaWIFS. Reanalysis data such as HYCOM was also utilized in this research. Results from HYCOM data show that there has been a 0.0098 °C increase in the sea surface temperature per decade in Busuanga while MODIS data indicates an increase of 0.0045 °C per decade. Moreover, HYCOM data also shows an overall average of 0.76 mm in sea surface elevation anomaly and a decreasing trend in salinity values at 0.0026 psu per decade. Chlorophyll-a concentration has a minimal increase based on results from MODIS and SeaWIFS. Aside from changes in water parameters, changes in the land also affect seagrasses. Forest loss may cause increased siltation in the coastal ecosystem which can lead to seagrass loss. Based on the results of Landsat satellite image processing, there has been forest cover loss in Busuanga with the highest loss occurring in 2013 when super typhoon Yolanda ravaged the island. Lastly, results from the linear spectral unmixing of 778 Landsat images from 1987–2000 show that the average percent cover of seagrasses in Busuanga were declining through the years.

This paper demonstrates the effects of terrigenous sediment load reduction by watershed managements on coastal turbidity in Banate Bay, Iloilo located in central Philippines, using field observations and numerical simulations. Measurements of the total suspended solid and particulate organic carbon indicated that the bulk component of the coastal turbidity comprised terrigenous mineral particles rather than phytoplankton at the rise of the river after heavy rain. The suspended sediment concentration and underwater light intensity were simulated by an atmosphere-watershed-coastal ocean model to investigate the contribution of the terrigenous sediment load to the coastal turbidity in rainy season. The coastal sediment simulation indicated that the turbidity in Banate Bay is highly impacted by terrigenous sediment inputs from distant watersheds, which are transported to the bay by coastal currents. In contrast, the contributions of sediment loads from the adjacent watersheds to the bay turbidity were limited. The simulation also indicated that the majority of the bay is not inhabitable for seagrasses due to limited light availability caused by the high turbidity. Scenario analysis of the sediment load reduction demonstrated that significant reduction of turbidity and improvement of light penetration are conditionally expected only when the remediation is implemented with cooperative management of a series of neighboring watersheds because of the significant contributions of sediment loads from multiple basins.

The predominantly agricultural coastal watershed located in tropical–subtropical Island has served as a pathway for nonpoint source (NPS) pollution loading into the downstream coastal ecosystems. The present study aims to assess watershed hydrology and water quality by applying a watershed model to long–term high–resolution monitoring data, and to evaluate the reduction of nonpoint–source pollution by implementing best management practices (BMPs) in a small agricultural watershed located in southwestern Japan. The Soil Water and Assessment Tool (SWAT) was coupled to a groundwater model (MODFLOW) and applied to simulate stream flow, sediment, and nutrients discharges. The results revealed that the model successfully predicted hourly stream flow, sediment, and nutrients concentrations in the study watershed and that the model could be further used to evaluate BMP scenarios. This is the first attempt to quantify the impacts of multiple agricultural mitigation measures on long-term water quality for sediment, nitrate, and phosphate at an hourly resolution. From the model results, the land cover conversion and mulching scenarios achieved a significant reduction in sediment, followed by the cover crop, alternative tillage, and filter strip scenarios. Moreover, conversion of all summer sugarcane to pasture farmland and fertilizer control scenarios gave the superior reduction in nitrate load, while other scenarios were minimally effective. On the other hand, most of the scenarios significantly achieved the reduction of phosphate load. The results further indicated that the BMPs recommended in this study are appropriately combined scenarios, which achieved the significant reduction in all NPS loads. Although this study revealed some effective mitigation measures to improve the water quality in the study watershed, actual implementation of correct ones may be practically challenging unless other environmental and economic risks (e.g. the increase of other pollutants and reduction in agricultural productivity) are also taken into considerations.

Because scour is one of the main reasons for bridge failure, this study focuses on accurately predicting the maximum scour depth around different vertical and inclined piers. Scouring is an issue o...

Mangroves, which are vulnerable to natural threats and human activities on small islands in the tropics, play an essential role as carbon sinks, helping to mitigate climate change. In this study, we discussed the effect of natural factors on mangrove sustainability by analyzing the impact of rainfall, land surface temperature (LST), and tidal inundation on the greenness of mangroves in Karimunjawa National Park (KNP), Indonesia. We used Sentinel-2 image data to obtain the normalized difference vegetation index (NDVI) and normalized difference moisture index (NDMI) during the dry season to determine the effect of inundation on mangrove greenness and soil moisture. The tidal inundation area was calculated using topographic data from the KNP and tidal observations from the area adjacent to it. Unmanned autonomous vehicles and topographic data were used to estimate mangrove canopy height. We also calculated mangrove greenness phenology and compared it to rainfall from satellite data from 2019–2021. Results show that the intertidal area is dominated by taller mangroves and has higher NDVI and NDMI values than non-intertidal areas. We also observed that mangroves in intertidal areas are mostly evergreen, and optimum greenness in KNP occurs from February to October, with maximum greenness in July. Cross-correlation analysis suggests that high rainfall affects NDVI, with peak greenness occurring three months after high rainfall. The LST and NDVI cross-correlation showed no time lag. This suggests that LST was not the main factor controlling mangrove greenness, suggesting tides and rainfall influence mangrove greenness. The mangroves are also vulnerable to climate variability and change, which limits rainfall. However, sea-level rise due to climate change might positively impact mangrove greenness.

Several ecological and biogeochemical processes in mangroves are influenced by crab activities through bioturbation, leaf litter consumption, or fecal deposition. Bioturbation might be influenced by crab burrow dynamics or surrounding abiotic and biotic factors or both. Therefore, it is necessary to examine burrow dynamics under different abiotic and biotic conditions. This study was conducted in the estuarine mangroves of Fukido River in the northern part of Ishigaki Island, Japan. Two transects consisting of five and seven 14-m diameter circular plots were established perpendicular to the mangrove/ocean interface. Spatial and seasonal burrow dynamics data were collected from five randomly chosen quadrates within each plot. Burrow density, renewed burrows per day, and collapsed burrows per day significantly varied spatially and seasonally. Burrow density strongly depended on sediment bulk density. Numbers of renewed and collapsed burrows per day were the same (R2 = 0.86) though they significantly differed among the four seasons with being lowest in the winter season. This suggests that temperature, precipitation and crabs occurrence might control seasonal burrow dynamics. Proportion of collapsed burrows were strongly and significantly correlated to sediment bulk density, salinity and sediment temperature, which suggests that sediment properties provide structural support for burrows maintenance. On the other hand, vegetation cover and sediment characteristics influence the proportion of renewed burrows. Burrow depth was significantly controlled by sediment particle size, which suggests that crabs do not create deeper burrow if sediments contain higher amount of coarse sand. Entrance diameter was correlated to percentage organic matter, salinity, fine sand and distance from the river that means seaward sites are occupied by smaller and shallow burrows. Our results suggest that the burrow dynamics depend on abiotic and biotic factors and are useful for understanding spatial and seasonal variations for estimating bioturbation effects on mangroves biogeochemical cycle.

Mangrove forests protect the coasts from natural disasters such as storm surges and tsunamis. These ecosystems also deposit sediments—a key process in carbon sequestration and adapting to rising sea level. These services provided by mangroves are related to their drag effect that significantly attenuates flow and waves, and enhances sedimentation. The drag force exerted by mangroves is due to the complex structures of their above-ground roots. A key parameter for the quantitative assessment of drag force is the projected area of vegetation. In this chapter, we focus on the above-ground root system (prop roots) of Rhizophora—the most dominant genus in the Asia-Pacific region and likely to exhibit the highest drag among mangrove species—in exploring the projected area of vegetation. We describe the methods of field measurement and an empirical model for the projected area of the Rhizophora prop root system. The results show the allometric relationships between the prop root projected area and tree size, and how the allometric relationships vary depending on the sites. The developed model shows its great ability as well as some limitations in accurately predicting the projected area of prop roots. We then discuss the environmental factors that may affect the allometric relationship, and prospects in developing the universal model, which can predict the prop root projected area in any type of environment. We also discuss perspectives in the measurement and modeling of other types of mangrove above-ground root system such as pneumatophores of Avicennia and Sonneratia species.

Using monitoring data from 1998 to 2017, we examined the spatiotemporal pattern of disturbances that occurred in Sekisei Lagoon, surrounded by Iriomote and Ishigaki islands in Okinawa, Japan. Outbreaks of crown- of-thorns starfish ( Acanthaster cf. solaris ), coral bleaching, typhoon damage, snail predation, and occurrences of growth anomalies, black band disease, and white syndrome were investigated using generalized linear models. Likelihood ratio test indicated that the type of coral assemblage, topographic features, and geographic range of research sites affected the occurrence of each disturbance. The sites dominated by Acropora spp. and the sites located in Sekisei Lagoon suffered recurrent and multiple disturbances. The impacts of disturbances on coral cover were evaluated using generalized additive models. Model averaging using Akaike information criteria revealed that a loss of coral cover occurred even when only a few A. cf. solaris were present, when the bleaching rate was sufficiently high, or when typhoon damage was severe. Our study describes spatiotemporal patterns of disturbances over a 20-yr period and reveals their relative impacts on coral cover. Our findings may be useful in predicting the responses of coral communities to future climate change scenarios.