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Diet assimilation rate is crucial to the growth and survival of Holothuria scabra juveniles during culture. To understand the assimilation rate and efficiency we assess organic carbon assimilation, which is closely related to the growth and source of variations in diet. We conducted a two-factor experiment, i.e., juvenile origin (cultured and wild H. scabra juveniles), and diet treatment (one control with no additional diet, and three additional diets, i.e., rice bran, dried cow manure, and seagrass Enhalus acoroides extract). We monitored the amounts of each diet that the juveniles consumed and the fecal pellets they egested. The diet, sediment, body walls, and organic carbon content of the fecal pellets were measured using an elemental analyzer combined with an isotope ratio mass spectrometer. Exponential growth was seen in the juveniles fed with rice bran, which had a fecal pellet egestion of 0.12–0.21 gC/d. Stable isotope analysis showed that the contribution of the diet proportion to the growth of the sandfish did not exceed 30%. The range of the assimilation rate was 35.3–62.4 gC/d. The average assimilation efficiency of organic carbon was 43.6 ± 27.7% (max 57.9%). Considering the assimilation rate and efficiency, we suggest a feeding interval of once every two days or twice per week at a rate of 3–5% of the total H. scabra biomass for a juvenile culture system.

Nutrients are important compounds in waterbodies that regulate primary productivity and phytoplankton growth, the basis of food webs. Increased nutrient concentration has become a serious concern because it causes eutrophication and threatens the sustainability of ecosystems. Eutrophication is the process of nutrient enrichment in water bodies that affects their productivity and decreases water quality. Although information about nutrient distribution, limiting nutrients, and nutrient budgets is important for coastal water management, studies of wide-scale nutrient dynamics in Indonesian waters remain limited. To provide comprehensive data on nutrients, this review summarized the concentrations and compositions of nutrients in coastal waters, compared the limiting nutrients in various coastal waters based on the Redfield ratio, and described the factors affecting nutrient budgets using the database in ScienceDirect and Google Scholar. Curation was performed to summarize the nutrient dynamics in coastal waters. Results showed that nutrient concentration differed in each region due to many factors. Anthropogenic inputs greatly affected nutrients in tropical areas, such as Jakarta Bay (Indonesia). Understanding the quality and characteristics of water can help in managing waterbodies. This study provided knowledge related to nutrient dynamics in Indonesian waters and global biogeochemistry.

Deoxygenation is increasingly recognized as a significant environmental threat to the ocean following sea temperature rises due to global warming and climate change. Considering the cruciality of the deoxygenation impacts, it is important to assess the current status and predict the future possibility of ocean deoxygenation, for instance, within the Central Indo Pacific (CIP) regions represent climate-regulated marine areas. This study divided CIP into five regions then investigated the deoxygenation parameters (dissolved oxygen, temperature, salinity, and pH) collected from 1993 to 2021 sourced from in situ measurement and long-term hindcast data. The overall error statistics indicate a good accuracy of hindcast data and are comparable to the in situ values. The surface waters were identified to have the most fluctuated seasonal pattern of dissolved oxygen (DO) concentration compared to other water columns. However, DO fluctuation occurred in a different pattern in each region. The study shows ocean deoxygenation is accelerated in all five regions over decades. The strongest oxygen minimum zone (OMZ) is identified in the Bay of Bengal and the Arafura Sea with the lowest oxygen concentration less than 0.5 mmol/m

Particulate organic carbon (POC) is one of the essential variables in oceanic biogeochemical processes. Assessing the spatiotemporal variability of POC will help deepen our understanding of the carbon cycle. In this study we collected moderate-resolution imaging spectroradiometer (MODIS) Aqua satellite data for surface POC in Indonesian waters during the period 2002–21, together with in situ data from the south-western Sumatran waters (SSW), Sunda Strait, Sumba–Savu waters and the Halmahera Sea and surrounds. These data were analysed to gain an understanding of the spatial and temporal variations in POC. Generally, high POC concentrations in Indonesian waters were found at coastal and continental shelves connected to the estuaries of large rivers; we assume that the POC concentrations in these areas are affected by terrestrial input. Meanwhile, in Indonesian waters apart from these estuaries, marine-derived materials are the main components of POC. The seasonal pattern of POC in Indonesian waters generally shows highest levels during the south-east monsoon and lowest levels during the north-west monsoon. Trends in POC concentrations are positively correlated with chlorophyll-a and negatively correlated with sea surface temperature. This study suggests that the combination of natural physicochemical processes and anthropogenic perturbations has significant effects on spatial and temporal variations in POC in Indonesian waters.

In terms of downward transport, suspended particulate matter (SPM) from marine or terrigenous sources is an essential contributor to the carbon cycle. Within mesoscale environments such as seagrass ecosystems, SPM flux is an essential part of the total carbon budget that is transported within the ecosystem. By assessing the total SPM transport from water column to sediment, potential carbon burial can be estimated. However, SPM may decompose or reforming aggregate during transport, so estimating the vertical flux without knowing the decomposition rate will lead to over- or underestimation of the total carbon budget. Here this paper presents the potential decomposition rate of the SPM in seagrass ecosystems in an attempt to elucidate the carbon dynamics of SPM. SPM was collected from the seagrass ecosystems located at Sikka and Sorong in Indonesia. In situ experiments using SPM traps were conducted to assess the vertical downward flux and decomposition rate of SPM. The isotopic profile of SPM was measured together with organic carbon and total nitrogen content. The results show that SPM was transported to the bottom of the seagrass ecosystem at a rate of up to (129.45±53.79) mg/(m2·h) (according to carbon). Considering the whole period of inundation of seagrass meadows, SPM downward flux reached a maximum of 3 096 mg/(m2·d) (according to carbon). The decomposition rate was estimated at from 5.9 µg/(mg·d) (according to carbon) to 26.6 µg/(mg·d) (according to carbon). Considering the total downward flux of SPM in the study site, the maximum decomposed SPM was estimated 39.9 mg/(m2·d) (according to carbon) and 82.6 mg/(m2·d) (according to carbon) for study site at Sorong and Sikka, respectively. The decomposed SPM can be 0.6%–2.7% of the total SPM flux, indicating that it is a small proportion of the total flux. The seagrass ecosystems of Sorong and Sikka SPM show an autochthonous tendency with the primary composition of marine-end materials.

The western waters of North-Sumatera experience dynamic environmental changes during the onset monsoon of the Asian winter. Those changes certainly will affect the distribution of marine organisms, especially the plankton. Plankton is the foundation of the aquatic food chain and plays an important role as the entry gate of solar energy to the water trophic systems. This study aims to investigate the plankton community and its correlation with the environmental factors during the onset monsoon of the Asian winter. Plankton samples were collected, along with water samples and in-situ measurement for environmental parameters determination from western waters of North-Sumatera (95°E – 93°N) in November-December 2017. Plankton samples were taken by vertically hauling (500 m) using Modified Twin Plankton Net with 80 µm mesh size for phytoplankton and 300 µm for zooplankton. Temperature, salinity, and density of waters were measured using CTD SBE 911 – Plus. The nutrients, including orthophosphate, nitrate, and silicate, measured using autoanalyzer Skalar SAN++. Thirty genera of phytoplankton and 44 taxa groups of zooplankton were found. The phytoplankton community dominated by Thallassionema, while the zooplankton dominated by Calanoida. There was a difference in the composition of plankton communities between the north and south parts of the study area. It was probably influenced by different water masses between those two regions indicated by the dissimilarity of their water characteristics. Based on the analysis of the T-S diagram, it is likely that the north community influenced by Bengal Bay Water while the south community influenced by the Indian Equatorial Water.

Seagrass meadows provide critical ecosystem services for coastal areas, e.g., as nursery habitats for various fish species, help with water filtration of suspended sediment, and provide food for dugongs (Dugong dugon). Their role as “blue carbon” and their capacity to mitigate climate change, by means of Natural mechanism of Carbon Dioxide Removal (NCDR) from the atmosphere, has recently gained increased attention. However, available scientific methods such as guidelines and manuals to measure carbon stock and sequestration still rely heavily on field sampling activities and laboratory analyses. Despite their accuracy, neither of these methods are applicable for large-scale carbon inventories nor are they practical in areas with limited carbon-related data and laboratory resources. Thus, it is necessary to determine whether any of the seagrass-related variables (e.g., coverage, density and biomass) may be treated as a proxy that are both robust and practical to assess the capacity of seagrass to store and sequester carbon. We developed formulas, assessed their robustness, and used both the formulas and the proxy to estimate carbon stock and the sequestration potential of the seagrasses. Furthermore, this study aims to elucidate the carbon stock and sequestration potential capacity of the seagrass ecosystems in Indonesia. We used the data of seagrass- and carbon-related variables obtained from eleven study sites and developed several candidate formulas using the Robust Linear Mixed Models (rL MMs). We found that the best formulas are comprised of multiple seagrass-related variables that consistently include biomass and coverage. This suggests that a combination of biomass and coverage is the best proxy to estimate carbon stock; however, a single proxy of seagrass coverage is recommended for practical seagrass monitoring purposes by the local government. Estimations of carbon stock and sequestration subsequently follow the formulas in the present study. Here we estimated, using a single proxy of seagrass coverage, that the above- and below-ground carbon stock, and carbon sequestration capacity of seagrass ecosystems in Indonesia reached 80–314 ktC, 196–696 ktC, and 1.6–7.4 MtC/year, respectively.

Saat awal monsun Asia musim panas (onset summer of Asia monsoon) di bulan Juni-Juli-Agustus, perairan sekitar Pulau Simeulue, Aceh, terpengaruh oleh kejadian upwelling di Samudra Hindia. Hal ini diduga mempengaruhi siklus gas karbondioksida antara laut dan udara di perairan sekitar Pulau Simeulue, Aceh. Pada kegiatan survei Ekspedisi Widya Nusantara (EWIN) 2017 #coastal chapter yang dilaksanakan bersama Pusat Penelitian Oseanografi (P2O) LIPI bulan Juli 2017 didapat data temperatur, salinitas dan tekanan parsial gas CO2 (pCO2) di laut. Tujuan dari penelitian ini adalah untuk melihat interaksi laut-atmosfer dan menentukan serapan atau luaran karbon di sekitar Pulau Simeulue. Untuk data pendukung berupa kadar CO2 di udara didapat dari Stasiun Pemantau Atmosfer Global Bukit Kototabang, Sumatra Barat. Dengan melakukan perhitungan flux CO2 antara laut dan udara, didapatkan hasil bahwa perairan di wilayah barat pulau berperan sebagai penyerap karbon (sink) dengan nilai fluks -0,05 mol C/m2 hari hingga -0,25 mol C/m2 hari. Sementara itu pada wilayah timur pulau memiliki peran sebagai sumber karbon (source) dengan nilai fluks 0,05 mol C/m2 hari hingga 0,2 mol C/m2 hari. Nilai fluks positif berarti laut melepaskan karbon ke udara dan sebaliknya nilai negatif berarti laut menyerap karbon.

Trace metals are vital to primary productivity and play an essential role as main components in regulating oceanic biogeochemical cycles. Dissolved and particulate trace metals within the water column may vary due to primary production, temperature, and nutrient changes, factors that may also vary spatially and temporally. Furthermore, assessment of trace metals mainly relies on in situ observation, and so wide-area investigation of trace-metal concentration may be challenging and subject to technical constraints. A specific approach is therefore necessary that combines biogeochemical proxies, satellite data, and trace-metal linear correlation. This study aims to assess the potential spatio-temporal variability of sea surface cadmium (Cd) and copper (Cu) concentrations in Indonesian seas and surrounding areas. The correlations of Cd and Cu concentrations with primary production and nutrient data were used to convert hindcast satellite data into estimates of the metals’ concentrations. The potential variability of trace metals can be determined by overlaying both data. Indonesia’s Fisheries Management Areas (FMAs) were used for data clustering and analysis. The results show that Cd and Cu trace metals have similar distribution patterns throughout the year. However, dissolved Cu has a more diverse coverage area than dissolved Cd, including within the Halmahera, Seram, and Maluku Seas (FMAs 716 and 717), the Makassar Strait (FMA 717), and the Java–Sumatra upwelling area (FMA 573). Both Cd and Cu concentrations in the Java–Sumatra upwelling region follow the periodic upwelling pattern. Overall, both Cd and Cu show a declining trend in concentration from 2012 to 2019. It is estimated that dissolved Cd concentration declined from 1500–2000 pmol/kg in 2012 to 1000–1500 pmol/kg in 2019 for all locations. Dissolved Cu concentration decreased from 30–35 nmol/kg in 2012 to 25–30 nmol/kg in 2019. Estimated dissolved Cd and Cu follow the linear functions of silicate (SiO4), nitrate (NO3), and primary productivity. The fluctuation of anthropogenic activities and global warming are likely to indirectly impact the decline in metal concentrations by affecting nutrients and primary productivity.

Seagrass carbon emission is mainly due to the land-use change; therefore, conservation will be an approach required for carbon offset. A method for estimating carbon offset from conservation activities has been developed. This study aims to evaluate the carbon-offset potential of the seagrass ecosystem by applying this method to five provinces in Indonesia. North Maluku has the widest seagrass area, but only 5% of this is the conserved area. Meanwhile, Jakarta has the highest percentage of its conserved seagrass within the area. Emission reduction at the year 2020 ranged 0.03-1.02 tC/year (with leakage) or 0.05-2.04 tC/year (without leakage). The percentage of emission reduction among the five provinces ranged from 0.75% to 11.3%. About 9.03 tC/year emission from seagrass ecosystems in Jakarta will decrease by up to 8.01 tC/year. Further assessment shows a positive correlation between the percentage of the conserved area and the percentage of emission reduction.

Trace metals are vital to primary productivity and play an essential role as main components in regulating oceanic biogeochemical cycles. Dissolved and particulate trace metals within the water column may vary due to primary production, temperature, and nutrient changes, factors that may also vary spatially and temporally. Furthermore, assessment of trace metals mainly relies on in situ observation, and so wide-area investigation of trace-metal concentration may be challenging and subject to technical constraints. A specific approach is therefore necessary that combines biogeochemical proxies, satellite data, and trace-metal linear correlation. This study aims to assess the potential spatio-temporal variability of sea surface cadmium (Cd) and copper (Cu) concentrations in Indonesian seas and surrounding areas. The correlations of Cd and Cu concentrations with primary production and nutrient data were used to convert hindcast satellite data into estimates of the metals' concentrations. The potential variability of trace metals can be determined by overlaying both data. Indonesia's Fisheries Management Areas (FMAs) were used for data clustering and analysis. The results show that Cd and Cu trace metals have similar distribution patterns throughout the year. However, dissolved Cu has a more diverse coverage area than dissolved Cd, including within the Halmahera, Seram, and Maluku Seas (FMAs 716 and 717), the Makassar Strait (FMA 717), and the Java-Sumatra upwelling area (FMA 573). Both Cd and Cu concentrations in the Java-Sumatra upwelling region follow the periodic upwelling pattern. Overall, both Cd and Cu show a declining trend in concentration from 2012 to 2019. It is estimated that dissolved Cd concentration declined from 1500-2000 pmol/kg in 2012 to 1000-1500 pmol/kg in 2019 for all locations. Dissolved Cu concentration decreased from 30-35 nmol/kg in 2012 to 25-30 nmol/kg in 2019. Estimated dissolved Cd and Cu follow the linear functions of silicate (SiO

Oxygen plays an essential role in the biogeochemical process and ocean productivity, especially during the recent trend of climate change. Development of the oxygen loss condition, deoxygenation, receives less attention than ocean acidification and warming. Therefore, understanding deoxygenation is indispensable. The maritime continent waters of Southeast Asia (SEA) are well-known for marine biodiversity and unique geological features. The area is inevitably impacted by climate change and will suffer more due to less oxygen in seawater. Based on previous research, Bengal Bay has been affected by oxygen depletion and climate change, in which hypoxic rate conditions continuously increase. In the other SEA area, seasonal hypoxia occurs in coastal areas as an impact of eutrophication. This occurs in Sangga Besar River Estuary, Bolinao and Anda coastal waters, Manila Bay, Jakarta Bay, and Cambodian waters. Deoxygenation anticipation is an essential step as a response to the development of oxygen loss areas, and monitoring is proposed as a preliminary step before the oxygen loss worsens. This review focuses on observing oxygen depletion changes and hypoxia in the maritime continent area, including its potency, effect, and recommendations on how to monitor deoxygenation.

We investigate variation in sediment carbon stock at Mempawah and Bakau Besar in West Kalimantan by analyzing organic carbon content from sediment samples taken within 20 cm depth. Our results show that organic carbon stock of sediments in Bakau Besar is generally higher than in Mempawah that may be due to riverine input of organic carbon into the mangrove forests. The riverine input of organic carbon is influenced tides, in which we find that organic carbon loads are higher during high tide compared to low tide. In particular, we find high organic carbon contents at a station in Mempawah (Station 3; 6.46 ± 0.23 tons C/ha) and another station in Bakau Besar (Station 2; 14.93 ± 1.43 tons C/ha). These two stations have mangrove density of 13,519 individuals/ha and 9,928 individuals/ha, respectively. We conclude that high organic carbon is influenced by riverine input as well as a high density of mangrove and the dominant type of mangrove vegetation at the sites.

Suspended particulate matter (SPM) has been known as an important variable in the organic matter flow of coastal ecosystem. Half of burial carbon in seagrass meadows is contributed by allochthonous sources that compose the SPM such as phytoplankton, seagrass detritus, marine snow aggregates and terrestrially derived particles. Each composition of the SPM contributes different roles and is important to be identified, for instance, the exact contribution of seagrass detritus will be useful for determination of carbon export through the detritus form in seagrass meadows. Here, the SPM of seagrass meadows is studied in Bintan Island and the Selayar Archipelago. The aim of this research is to determine the source origin of the SPM using a stable isotope signature. In order to fulfill this aim, the objectives are defined as: (1) to specify the stable isotope signature (δ13C and δ15N) of the SPM, and (2) to determine the proportional distribution of the SPM’s prospectus sources. The result shows that the possibility of the source origin of the SPM includes a seagrass fraction (Enhalus acoroides and Thalassia hemprichii), terrestrial C4 plant, macroalgae, and terrestrial C3 plant. The SPM lies between the marine- and terrigenous-end members. However, it seems that the SPM is more to be terrigenous-end and allochthonous. According to a Bayesian mixing model, the terrestrial C4 has the highest contribution of the SPM at all sites except Barugaia and Pasi Island in Selayar (i.e., the highest contribution of the SPM is from the detritus of E. acoroides). The second contribution has been contributed by either seagrass detritus (E. acoroides or Th. hemprichii) or terrestrial C3 plant. The finding of this study indicates that there is a strong influence of the terrigenous sources in the SPM of the seagrass meadows.

Sea level changes play an important role as an indicator of climate change. However, without climate change, the sea level itself shows strong regional patterns, both in space and time, that could deviate significantly from global averages. The spatial variability of sea level changes in Indonesia can be divided based on its drivers, i.e., climatic and seasonal weather-driven and non-climatic and geological-driven. Seasonally, the sea level in Indonesia is generally high in northwest monsoon and low in southeast monsoon. Nevertheless, there is a possibility of extreme natural phenomenon influences that generate anomalies and a thermosteric process that also affects the sea level. On the non-climatic and geological theory, the uniqueness of the tectonic setting in Indonesia will create spatial variations in regional sea levels, as both static and dynamic changes in a long period of time. Land subsidence is also often regarded as a significant contributor to the rise of relative sea level in coastal environments. Combined with the rise in sea level, land subsidence will escalate coastal flooding risks, contribute to shoreline retreat, and be further aggravated by anthropogenic forces such as groundwater extraction and land development. This scientific review will summarize the spatial variation of sea level rise in Indonesia, examines the underlying drivers that control it, and provides an overview of the combined sea level rise and land subsidence as a significant threat in Indonesia.

The biogeochemical cycle of trace metals is very likely affected by the global change in the ocean, especially due to the increasing of sea surface temperature and acidity. Thus, assessing biogeochemical cycle of trace metals will beneficial in elucidating the potential impact of climate change as well as ocean acidification. The assessment of the biogeochemical cycle of trace metals can be performed by measuring trace metals fluxes crossing the sediment–water interface. The main challenge in this measurement is the difficulty of measuring metal concentrations at trace levels due to either physical factors or biological factors that can affect the total flux. Sediment porewater profile and in situ benthic incubation are the two most commonly used methods for measuring trace metals fluxes from sediment to the overlying water or vice versa. The coefficient of diffusion and gradient of concentration are the two most important values in the sediment porewater profile method, while the constant volume involved in the container during the experiment is an important part of the in situ benthic incubation method. The purpose of this review is to provide an overview of both measurement methods deeply and predict the challenges faced in its implementation in Indonesia.

The emission of greenhouse gases, including high CO2 and other materials, initiates global warming and climate change. Atmospheric CO2 that affects the carbonate system of seawater causes ocean acidification (OA). OA affects marine organisms directly, as well as humans economically and ecologically. Considering the high impact of OA and following the United Nations' Sustainable Development Goals, systematic research and monitoring of OA is necessary in Indonesia, whose seas play an important role in this emerging phenomenon. This review discusses the urgency of OA monitoring systems and suggests carbonate system monitoring, as well as carbon biogeochemistry. OA significantly affects marine production and alters ecosystem services, and it is likely to have an impact on habitats shifting from calcified to non-calcified and reducing benthic complexity. Its effect on calcifying organisms can also be found, i.e., coral calcification and/or dissolution of CaCO3 of calcifying organisms. Acidity (pH), as well as the carbonate system variables of seawater, fluctuate, especially with variations in space and time. Coastal ecosystems that are directly affected by terrestrial input will have carbonate system variables that fluctuate more. The annual rate of decreasing seawater pH, especially over an open and large spatial scale, may indicate OA. Therefore, a monitoring system must be implemented to obtain systematic and comprehensive information on OA. Here, we also introduce a biogeochemical monitoring initiative for OA in Lombok with the established protocols. Improvement of many aspects, including analysis instruments, analysis methods, sample treatment, and sampling frequency will provide new insight into further research and monitoring of OA.

Ongoing global changes such as increasing sea-surface temperatures, decreasing acidity levels, and expanding oxygen-minimum zone may impact on the biogeochemical cycles of trace metals in ocean systems. Each trace metal has unique characteristics and a distinctive distribution pattern controlled by chemical, biological, and physical processes that occur in ocean systems. The correlations of variability drivers in trace metals are interesting topics for investigation. Following up on ocean research in the coastal and estuary area, we specifically review the distribution of trace metals in seawater and suspended and surface sediment. The marginal seas usually feature significant terrestrial inputs accompanied by several active water-mass currents. The purpose of this review is to provide an overview of variability related to trace-metal distribution in coastal and estuary systems and to specifically describe the distribution, profile and drivers that affect trace metals variability.

Sea cucumbers are an essential fishery resource. Therefore, effective aquaculture methods should be developed to achieve their optimal production. Sea cucumbers are susceptible to various environmental factors, one of which is water quality. Monitoring water quality based on physical and chemical parameters should be useful to the rearing system in aquaculture. In practical use, farmers usually monitor only temperature, salinity, and pH, neglecting the essential role of chemical parameters. This review focuses on and urges the monitoring of physical and chemical parameters. We explored the water quality parameters that may be crucial to the sea cucumber rearing system, including temperature, salinity, pH, dissolved oxygen, ammonia, turbidity, particulate organic matter, total nitrogen, nitrate, nitrite, ammonium, silicate, and phosphate. Furthermore, this paper presents a practical way to monitor the aquaculture or rearing system of sea cucumbers. It is suggested that temperature and salinity are the crucial physical parameters, while the essential chemical parameters are phosphate, nitrate, and ammonia.

It has been widely known that the Indonesian Throughflow (ITF) is an important inter-ocean connection with unique and complex oceanographic and geographic conditions, as well as a strong relation to both regional and global ocean currents and climate systems. Many studies on characteristics, mechanisms, and impacts of the ITF have been conducted, mainly focusing on the ITF pathways, transport, water mass mixing processes, and their variability in connection with monsoons and climate systems. In this paper, we summarize some of the critical aspects related to ocean conditions within the Indonesian Seas and the Indonesian Throughflow, with the main focus on studies of marine biogeochemistry in a region affected by the ITF. Although the biogeochemical cycle is one of the key research topics that are needed to advance our ocean understanding, studies on marine biogeochemistry within the Indonesian Seas are quite limited due to less observed data compared to the physical parameters. Further studies on biogeochemistry and efforts to conduct in situ and remotely sensed observations in this region are strongly required. Here, we propose several biogeochemical observations correlated to the ITF.

The increase of anthropogenic carbon dioxide (CO2) since the industrial revolution era affects the global carbon cycle and triggers climate changes. Indonesia has ratified the Paris Agreement and declared the emission reduction for climate action (Sustainable Development Goal 13) up to 29% (independently) or 41% (with international support) in 2030 relative to the business as usual (BAU) scenario. The effort to achieve this target is implemented on Low Carbon Development Initiative (LCDI) starting in 2020. LCDI adopts marine and fisheries as one of the implementing sectors that focus on blue carbon. To implement the activities as part of the carbon emission reduction within the LCDI, we have to establish a calculation method that should be measurable, reportable, and verifiable (MRV). The present article introduces the MRV method for calculating the carbon emission reduction for the Conservation/Protection Seagrass Ecosystem’s climate change mitigation activity on Marine Protected Area (MPA). We present how to calculate the baseline emission (business as usual), emission leakage when implementing the activity, and emission reduction. A case study on seagrass meadows of Kepulauan Seribu MPA is presented for the trial of the introduced method and formula. Using the proposed method is reliable enough to estimate carbon emission reduction from seagrass conservation activity within the MPA. We can calculate the carbon emission will reduce 4.35 tC relative to the BAU on Kepulauan Seribu MPA by 2030.

The Indian Ocean is influenced by monsoon system s which alter the ocean’s physical and chemical properties. Specifically, the south western Sumatran waters in the eastern Indian Ocean are considered a dual current regulated zone i.e. affected by S outh E quatorial C ounter C urrent (SECC) and S outh Java C urrent (SJC). This area is considered as having an important role in the transfer of organic matter or the biological pump. However, the information about this area is minimal , especially in term s of organic matter and nutrient profile. This study will update the recent information about the area, including the profile of particulate organic matter (POM) , macro-nutrient s , total suspended solid s (TSS) , macromolecule-degrading bacteria, and soft bottom macrobenthic organisms sampled from 26 stations in both the SECC-regulated zone and the SJC-regulated zone. The physical profile is typical of tropical waters and both zone s have a distinct profile of organic matter and nutrient s . The particulate organic carbon (POC), particulate organic nitrogen (PON), and TSS of the SECC-regulated zone can be considered higher than those of the SJC-regulated zone. This region is categorized as mesotrophic waters, especially from the surface up to 100 m. The production of nutrients and organic matter in the water column in this area contribute significantly to the abundance of heterotrophic bacteria and benthic organisms.

The Southwestern Sumatran Waters of the Eastern Indian Ocean are known to be affected by the South Java Current and the South Equatorial Counter Current. Many studies have been carried out in relation to upwelling and the Indonesian Through Flow. However, there has been no systematic study into the properties of the particulate organic matter in the Southwestern Sumatran Waters. Therefore, the organic matter in these waters in terms of its origin is unknown. As part of the Widya Nusantara Expedition 2015 research cruise, this study aimed to examine the stable isotope ?13C signature of particulate organic matter (POM), especially with regards to the origins of the organic matter. The stable isotope ?13C is complemented by other variables such as chlorophyll-a, particulate organic carbon (POC), and nutrients (phosphate, silicate, ammonium and nitrate). The POC tends to be depth-dependent. The values of ?13C are ?23.56, ?24.30 and ?24.06‰ for 5, 100 and 300 m depths, respectively. We found that POM tended to be isotopically lighter with increasing POC and chl-a, especially in the surface water, potentially due to the preferential lighter carbon isotope for metabolism by the primary producer. The origin of POM in the Southwestern Sumatran waters is marine end-member in the surface (up to 100 m depth) and mixed compositions at the surface of twilight zone (100–300 m depth). The next layer, i.e. twilight zone (more than 300 m depth), is terrigenous end-member. The surface POM of SSW, as shown in 5 m depth, is not freshly produced and tends to be either autochthonous or allochthonous.

Particulate organic matter (POM) is formed by the organism’s fecal pellets, phytodetritus of sinking plankton, and marine snow aggregates. It is exported downward from the euphotic zone. This process is an essential factor in the biological pump of aquatic ecosystems. It has been known that the coastal and open sea POM properties are different due to the origin of the materials. For instance, the terrestrial organic matter will strongly affect the composition of POM in coastal water compared to the open sea. However, some studies indicated that the physical and chemical processes in the marine environment alter that general pattern. Since the Indonesian water has unique features, i.e. water mass from other waters (the South China Sea, Pacific, and the Indian Ocean), upwelling and the existence of Indonesian Through Flow (ITF), the POM properties will be greatly transformed. There are few studies about POM spatial distribution and its isotopic profile in the Indonesian marine waters. This study used stable isotope in term of profiling the POM, especially to elucidate its organic matter origin. The sampling sites represent the eastern Indonesian waters (RCO-IOCAS cruise tract). This study can enhance the POM properties of the Indonesian waters which have never been studied before. The preliminary result shows that POM within 1000 m depth is stratified as the marine-end member (up to 100m) and mixed composition (up to 300m). This finding indicates that the vertical profile of the water mass relates to the biological pump through the vertical flux of POM.

Variation of Air-Sea CO2 Fluxes in Bintan Island Coastal Water. Eastern part of Bintan coastal water plays a major role as CO2 sink. However, flux and partial pressure of CO2 (pCO2) dynamically follows spatio-temporal variability. Spatio-temporal variability of CO2 flux may shows the whole condition of Bintan Island coastal water, especially in correlation with the primary production. Systematic study on variability of CO2 flux from or to the watern column is essential to understand the whole conditions of Bintan Island coastal water. This study aims to understand the spatio-temporal variation of CO2 fluxes in Bintan Island coastal water, and the factors influencing it. This study was conducted in the eastern part of Bintan coastal water in April and August 2014. In addition, this study was also conducted in the southern and northern parts in April 2016. CO2 fluxes dynamics were calculated from pCO2 (surface water and atmosphere), temperature, salinity, and wind speed. The result showed that almost all parts of the Bintan coastal water were carbon sources during first transition season. The largest CO2 emission was observed in the northern part (4.02 ± 1.92 mmol/m2/d) followed by the southern part (2.28 ± 0.80 mmol/m2/d) and then the eastern part (0.46 ± 0.28 mmol/m2/d). The eastern part temporally turned into CO2 sink in the southwest monsoon season (-0.27 ± 0.10 mmol/m2/d). Temperature was the main factor causing spatial and temporal variability of air-sea CO2 fluxes in the Bintan coastal water. Spatially, the presence of seagrass and coral reef ecosystems causes the partial pressure of surface water CO2 in the eastern part of waters of Bintan is much lower compared to the waters of north and south Bintan, thus emitting less CO2 to the atmosphere

Indonesia was recently ranked second on the list of countries producing plastic waste. Plastic can be degraded by thermal oxidation either with ultraviolet radiation and by mechanical to a very small size the size will be smaller. Degraded plastic with small sizes (

Fine seagrass detritus together with fecal matter, clumps of aggregated phytoplankton, and colloidal organic matter, comprise macroscopic organic aggregates known as ‘marine snow’. Seagrass phytodetritus is considered to be an important component of the carbon budget, because of the loss of carbon as fine particulate organic matter. The purpose of this study is to determine and to estimate the vertical flux of marine snow as part of the carbon budget in the seagrass meadows of Bintan Island. Average organic carbon and nitrogen fluxes were 8945.6±2742.0 mg C m −2 day −1 and 737.7±222.5 mg N m −2 day −1 , respectively. Considering the submerged time (5747 h in a year) also the total area (2600 ha), the vertical carbon flux of marine snow aggregates can be estimated as 557.6 g C m −2 yr −1 and 176.7 g N m −2 yr −1 throughout the year. The total carbon budget that was exported downward can be estimated as 14.5 kton C yr −1 . This vertical export is nearly one and a half times of the seagrass’s NPP in Bintan Island. The vertical carbon flux contributes a maximum nearly quadruple the decomposition + export of seagrass meadows. This result suggests that the dynamics of the flux of marine snow aggregates may contribute valuable information. According to the stable isotope analysis, the marine snow aggregates in seagrass meadows can be categorized as: (1) autochthonous (composed mainly of fine seagrass detritus) and (2) allochthonous (composed by POM, fecal pellets, anthropogenic inputs, etc.).

Climate change can be mitigated simultaneously by two ways, maintaining the greenhouse gases below the carbon budget and conserving marine and terrestrial vegetation for carbon sequestration. Marine vegetation (e.g. mangrove and seagrass meadows) is less than 0.5% of the total marine area and narrower compared to terrestrial vegetation. However, marine vegetation has high net primary production (NPP) and contributes more than 50% of the global carbon burial in its substrate and biomass. Indonesia has 3,301,848 ha of mangrove area, the widest in South-East Asia. The seagrass meadows of Indonesia are 150,693 ha, the second widest seagrass area in the world. These two ecosystems are important for the global carbon cycle due to their high capacity for carbon sequestration. Considering this potential, it is necessary to promote a strategic scientific-based policy of conservation of marine vegetation areas for both local and national stakeholders. The policies consist of: 1) to implement the National/Local Action Plan for Reducing Greenhouse Gas Emissions (RAN/D GRK); 2) to manage the land use changes that contribute 67% of total national emissions; 3) to determine coastal ecosystem protection areas that are considering the province policy in the Plan for Zoning of Coastal Areas and Small Islands (RZWP3K); 4) to rehabilitate terrestrial vegetation, coastal ecosystems, and aquatic conservation areas (President Regulation no 61/2011); and 5) to strictly carry out the national policy for green open space (Government Regulation no 26/2008).

Gaetice depressus is one of the most dominant macrozoobenthos species in boulder shores of intertidal coastal ecosystems in Japan. As recorded in previous studies, this species is also considered as having high density and biomass. Consequently, it is thought to be one of the more important species in the organic matter flow of boulder shores, especially through the food web. In this study, some taxonomic problems related to G. depressus were tackled and the autoecology and ecological processes in the intertidal ecosystem of G. depressus, such as organic matter flow, were investigated. Furthermore, in order to clarify the taxonomy description, resolve inconsistencies in the scientific name, and learn about the life history, a literature review was conducted. Seasonal changes in density, morphology pattern and population structure were determined based on the data obtained in Ebisu Island, Japan. Then, the role of G. depressus was determined by estimating the intake and emittance fluxes of organic carbon and nitrogen through ingestion and egestion process in the boulder shores of Ebisu Island. A feeding rate experiment was also conducted in order to estimate the intake flux by using the catch-release-recapture method. Meanwhile, to estimate the emittance flux, a defecation rate experiment was conducted by catching some individuals of G. depressus, and then incubating them in the laboratory. The feeding rate measured by the speed of diet consumption of G. depressus was about 12.6 mg ind-1 h-1. Considering the average density, the intake flux through the feeding process could be estimated as 25.2 mgC m-2 h-1 and 2.6 mgN m-2 h-1. On the other hand, G. depressus egested fecal pellet at the rate of 5.4 mg ind-1 h-1. The average emittance flux through the fecal pellet egesting process is estimated at 5.6 mgC m-2 h-1 and 0.7 mgN m-2 h-1. Therefore, it can be estimated that about 25% of organic matter from diet is egested as fecal pellet, which means that about 75% of the intake flux of organic carbon and nitrogen is used for the total assimilation of G. depressus. Intake flux was also considered as affecting the high dynamism of primary producer consumption. The total population of G. depressus is estimated to consume about 18.4% of primary producer in average throughout the year. Therefore, the turnover time of primary producer by consumption of G. depressus was about five days.

Biogeokimia sebagai ilmu sistem merupakan bidang yang relatif baru di Indonesia, jadi proyeksi kedepan perlu dilakukan untuk riset di bidang kelautan. Tujuan dari kajian ini adalah untuk memilah tren penelitian di bidang biogeokimia sekaligus menentukan kesempatan penelitian biogeokimia kelautan di Indonesia di masa yang akan datang. Analisis bibliometrik dipergunakan dalam kajian ini dengan basis data sitasi publikasi ilmiah sebagai sumber data utama. Kata kunci 'marine biogeochemistry' dipakai untuk memilah basis data secara otomatis. Analisis lanjutan yang lebih detil dilakukan pada publikasi pada tahun 2011-2013. Selain itu, data mengenai tema penelitian oseanografi pada Pusat Penelitian Oseanografi dan Badan Penelitian dan Observasi Kelautan. Berdasarkan analisis tersebut, prediksi tema riset biogeokimia kelautan di Indonesia dapat dilakukan. Topik yang mungkin menjadi riset kedepan adalah: efek pemanasan global terhadap mangrove dan terumbu karang, efek pengasaman air laut terhadap produksi primer atau organisme bentik, pergeseran distribusi spesies, peran biogeokimia spesies tertentu pada transfer materi organik. Sebagai bidang ilmu yang relatif baru, biogeokimia dapat menjadi bagian esensial pada berbagai kajian komprehensif pada ilmu kelautan, khususnya pada tema yang signifikan seperti perubahan iklim global dan pengasaman air laut. Kata kunci : bibliometri, biogeokimia kelautan, tren, global, proyeksi Biogeochemistry as the science system is relatively new field in Indonesia, therefore , projection is needed for the future research in marine science. The objectives of this study are to specify the trends in biogeochemistry research topics and to determine the opportunities for marine biogeochemistry research in Indonesia. Bibliometric analysis was used with citation databases as the main data. The keyword ‘marine biogeochemistry’ was used to sort the database. We conducted the further analysis mostly in publications from 2011-2013. The data about research themes related to oceanography in Indonesia were collected from Research Center for Oceanography and Institute for Marine Research and Observation). On the basis of the analyses, we tried to predict the likely main themes in marine biogeochemistry in Indonesia in the future. The likely topics are: the effects of global warming on mangroves and coral reefs, the effects of ocean acidification on primary production or benthic organisms, shifts in species distribution, and the biogeochemical role of certain species in organic material transfer. It is suggested that the relatively new discipline of biogeochemistry must be an essential part of any comprehensive study of marine science, especially in significant areas such as global climate change and ocean acidification. Keywords : bibliometry, marine biogeochemistry, trend, global, projection

Carbon Stock Estimation in Seagrass Biomass on Semak Daun Island, Thousand Islands. Seagrass ecosystem has a vital role in protecting the coastal ecosystem. It can also sequester and store carbon as an organic material (blue carbon) for a long time. However, anthropogenic activities in coastal areas give environmental stress on the seagrass ecosystem. This research was conducted to assess the carbon stock of seagrass biomass in Semak Daun Island in order to evaluate the potential of the seagrass meadows in sequestering carbon. Sampling and observation were held in the seagrass ecosystem to obtain seagrass density, biomass, frequency of occurrence, water quality, and anthropogenic activity. Carbon stock was calculated by the loss of ignition (LOI) method, and combined with density to determine the total carbon stock in the whole area of seagrass meadows. Seagrass species in Semak Daun Island consist of Halophila ovalis, Thalassia hemprichii, Cymodocea rotundata, Syringodium isoetifolium, and Halodule uninervis. The coverage area of seagrass in Semak Daun Island was 9.1 ha with carbon stock value of 1.84 ton C or equivalent to 6.76 ton CO2. Fifty two percent of the carbon stock was originated from the below-ground biomass and 48% from the above-ground biomass.

Gaetice depressus , a varunid crab common on intertidal boulder shores, is a potential key organism for monitoring organic matter flow through the food web. In order to elucidate its biogeochemical role, the diet source and trophic position of this crab on the boulder shore of an island off the Izu Peninsula, Japan, were estimated using three approaches: foregut content examination, stable isotope signature (δ 13 C and δ 15 N) and pigment biomarkers. The results suggest that G. depressus utilizes green macroalgae ( Ulva sp., Ulvaria sp.) as its main diet source together with red macroalgae ( Gloiopeltis complanata, Gl. furcata ). This crab also utilizes periphytic and planktonic microau-totrophs (occasionally tissues of heterotrophs) when macroalgae prove insufficient due to seasonal change. Therefore, G. depressus can be considered to be an omnivore since it consumes both autotrophs and heterotrophs, although it obtains organic matter mostly from autotrophs. Key words: diet source, foregut content

Karbon dioksida (CO 2 ) merupakan salah satu komponen gas rumah kaca yang berkontribusi dalam pemanasan global. Sebanyak 40 Tera ton karbon dioksida tersimpan di laut yang berperan penting dalam siklus karbon. Laut menyerap CO 2 melalui fotosintesis oleh komunitas plankton dan vegetasi pesisir (lamun dan bakau). Proses ini digunakan sebagai salah satu konsep dalam mengurangi efek gas rumah kaca. Pulau Bintan memiliki area padang lamun yang cukup luas. Potensi padang lamun, terutama dalam penyerapan karbon dioksida dapat ditentukan dengan menghitung cadangan karbon. Penelitian ini dilakukan pada bulan April 2016 di pesisir pulau Bintan (Teluk Bakau dan Pengudang). Spesies lamun Enhalus acoroides dan Thalassia hemprichii secara khusus menjadi target penelitian karena merupakan spesies dominan di perairan pesisir Pulau Bintan. Penentuan potensi cadangan karbon dilakukan dengan melihat estimasi cadangan karbon di dalam sedimen dan di habitus lamun, yaitu bagian di atas substrat (AS) yang terdiri dari daun dan pelepah daun, dan bagian di bawah substrat (BS) yang terdiri dari akar dan rhizoma. Tujuan lain dari penelitian ini adalah untuk mengetahui perbandingan cadangan karbon bagian AS dengan BS, serta antara kedua spesies tersebut. Hasil penelitian menunjukkan nilai cadangan karbon di Stasiun Pengudang (68.398,47 g C/m 2 ) lebih tinggi dibandingkan Stasiun Teluk Bakau (57.763,47 g C/m 2 ).Nilai estimasi cadangan karbon Enhalus acoroides secara umum lebih tinggi daripada Thalassia hemprichii baik di Stasiun Teluk Bakau maupun di Stasiun Pengudang. Sebaliknya, sedimen di Pengudang memiliki nilai cadangan karbon yang lebih tinggi dibandingkan di Teluk Bakau