Nearshore circulation plays an essential role in driving coastal processes that could intensify during extreme wind events. In tropical regions, like Indonesia, the probability of extreme winds increases under the influence of monsoonal seasons. Using the Delft3D-FLOW numerical model, this study investigates the response of nearshore currents to extreme wind forcing in Bangka Regency, a coastal area in the eastern part of Bangka Island, Indonesia. Two seasonal wind scenarios, representing west and east monsoon periods, are simulated under both existing and extreme wind conditions. Model validation against field-observed water level data shows good agreement (Willmott Score (WS) = 0.99, Root Mean Square (RMSE) = 0.07 m). Meanwhile, the comparison between modelled currents and the HYCOM datasets results in moderate WS values of 0.34–0.50 and RMSE values of 0.02–0.06 m for north–south, east–west, and current magnitude components, indicating the model’s reliability in capturing general hydrodynamic within the study area. Results reveal that tidal forcing is the dominant driver throughout the year, with the monsoonal seasons shifting the circulation patterns. Currents (average of 0.1–0.2 m/s, maximum of 0.5 m/s) predominantly flow towards the southeast during the west season and shift direction toward the northwest during the east season. Extreme wind events amplify the average current velocities twice as much as during monsoonal periods, with comparable predominant current directions. Currents are higher around headlands and shallow regions, whereas the velocities inside the embayment remain calm even during the extremes, highlighting the role of local geomorphology in modulating wind-induced flows, thus protecting the shoreline. These findings highlight the vulnerability of the East Bangka nearshore systems, or regions with similar settings, to climate-induced wind extremes, which may lead to various ecological hazards.

Enhalus acoroides is a well-known ecosystem engineer in the Indo-Pacific region. In this context, it plays a significant role in the protection of the coastline from coastal erosion and the maintenance of environmental conditions. This study investigates the physical characteristics of Enhalus acoroides and emphasizes their roles in shoreline stabilization and seawater filtration. A field survey was conducted in Prawean Beach, Jepara, Indonesia, using a transect quadrant to estimate the seagrass cover, supported by spatial analysis and a literature review. The results show considerable variation in leaf length, ranging from 30 to 114 cm, while leaf width remains relatively stable, ranging from 1.5 to 2 cm. Seagrass density ranges from 0 to 168 ind/m2, exhibiting strong spatial heterogeneity. The physical characteristics of Enhalus acoroides could reduce the wave energy by approximately 30% compared to smaller seagrass species. Additionally, the meadows play an important role in regulating sediment transport and facilitating the deposition of heavy metal within the substrate. Overall, these findings confirm that Enhalus acoroides functions as an effective natural coastal protector. Its integration into hybrid engineering approaches offers promising potential for coastal nourishment and sustainable shoreline management. Therefore, conserving seagrass habitat represents a crucial nature-based solution for enhancing coastal resilience and mitigating pollution.

Quantifying the combined effects of tidal forcing and seasonal variability on coastal water quality is crucial for managing semi-enclosed tropical embayments. This study investigated the spatiotemporal dynamics of water quality in Bungus Bay, Indonesia, during flood and ebb tides in the dry (June) and wet (December) seasons of 2020. A total of 11 physicochemical and nutrient parameters were analyzed using Pearson correlation, hierarchical clustering, principal component analysis (PCA), Coastal Water Quality Index (CWQI), and trophic state assessment. Clear tidal modulation was observed. Flood tides were characterized by higher salinity, lower nutrient concentrations, and predominantly good water quality (CWQI > 70). In contrast, ebb tides showed elevated nitrate, ammonia, phosphate, and total suspended sediment (TSS), with CWQI declining below 50 (poor water quality) at several inner-bay stations, particularly during the December survey. PCA revealed stronger nutrient structuring during the wet season, with nutrient-related variables dominating the first principal component and explaining more than 60

Seagrass ecosystems provide vital services but face increasing threats from human activities. Marine protected areas (MPAs) aim to mitigate these threats, but inadequate funding and management hinder effective conservation. Seagrass-associated tourism presents an opportunity to fund conservation efforts, enhance MPA implementation, and improve local livelihoods. This study explores stakeholder perceptions of seagrass benefits, tourism feasibility, and threats on Bintan Island, Indonesia, using quantitative (349 household surveys) and qualitative (focus group discussion with 15 participants) methods. Our findings show strong stakeholder support for seagrass-associated tourism, but challenges such as ongoing anthropogenic threats and governance shifts in MPA management remain to be addressed. For successful seagrass-based tourism and better conservation, ongoing engagement with local communities and stakeholders is crucial. This approach not only secures conservation funding but also fosters local ownership and stewardship. The study emphasizes understanding stakeholder perceptions to develop a sustainable tourism sector and ensure more effective, inclusive management strategies.

Located on the northern coast of Java Island, the coastal area of Cirebon is an area with rapid population growth and extensively developed as settlement areas, industrial estates, fisheries, agriculture, and public service infrastructures. Coastal dynamics issues have been occurring in the coastal area of Cirebon, which is characterized by significant changes in shoreline position. Moreover, some critical infrastructures are not functioning properly and may cause high maintenance costs and economic loss to the related stakeholders. This study aims to provide a greater understanding of the coastal dynamics along the 73.16 km of Cirebon shoreline through remote sensing and GIS methods supported by hydrodynamic analysis. This study applied coastal characterization, coastal structure identifications, and coastal processes assessments, including erosion and accretion analysis, hydrodynamic and tidal analysis, and inundation projection. The study indicates that some areas have been subject to significant erosion and accretion during the last two decades, with the total lengths of the eroded and accreted shoreline being -21.9 km (35.6%) and +39.6 km (64.4%), respectively. Furthermore, the coastal structures significantly influence the coastline's dynamic and mitigate the negative impacts of coastal floods. Jetty access channels in the west area have caused partial coastal erosion, while the breakwaters in the east area accelerated sedimentation processes and improved the growth of mangroves simultaneously. This study also simulated the potentially inundated areas by 2050 in four scenarios based on projected sea level rise, land subsidence, and extreme wave events. Policies to prevent such potential hazards are needed to avoid negative impacts on the living quality and vital economic sectors. This study provides insight into coastal characterization, potential coastal hazards, and their driving processes in time and space scale for coastal adaptation planning policies and sustainable coastal hazard management and mitigation.& COPY; 2023 Elsevier B.V. All rights reserved.

Water availability and management for water security on small islands are critical. The purpose of this research is to uncover the water resources issue at a small island community level as well as discourse on the potential threats and sustainable management for water security. Tunda Island, located in the Java Sea, is one of 81 small islands in Banten Province, Indonesia. Data were collected through focus group discussions, open interviews with key persons, direct field observations, and secondary data gathering. Moreover, we analyzed time series climate data, particularly rainfall and population growth projections, based on data from official Indonesian government sites. The monthly mean precipitation is ranging from a low of 48 mm/month in August to a high of 292 mm/month in January. A “surplus of water” occurs from November to May, while months with a “deficit of water” occur from June to October. The majority of the community is unaware of the water security issue due to a lack of information and knowledge in the community. Some threats to the sustainability of water resources would be caused by two factors, both anthropogenical and natural: rising water demand, diminishing groundwater reserves due to population growth and tourism activities on the island, drought, sea level rise, and seawater intrusion as climate-related impacts due to increasing population growth and tourism activities on the island and drought, sea level rise and seawater intrusion as climate-related impacts. Developing community knowledge and awareness of water security is the main issue that should be handled first, coinciding with sustainable management practices that consider water use efficiency, the use of alternative water sources (e.g., rainwater harvesting), and protecting and restoring coastal ecosystems, especially for the future tourist destination.

Indonesia has significant potential for the implementation of seagrass-associated tourism due to its high seagrass species diversity, large spatial-extent of seagrass meadows and abundant charismatic seagrass-associated species. Seagrass-associated tourism will not only increase the livelihoods of local communities but also have positive impacts on biodiversity within seagrass ecosystems. However, there are specific challenges that need to be addressed as a priority in order to promote sustainable seagrass tourism. These challenges include: (1) lack of awareness among the local communities about the potential of seagrass-associated tourism, (2) potential adverse impacts of tourism activities on natural seagrass ecosystems, (3) lack of standardized parameters for assessing the suitability of sites for seagrass tourism, and (4) lack of safety information for seagrass-associated tourism activities. To overcome these challenges, we propose a number of recommendations that will serve as a basis for promoting seagrass ecosystems as a new nature-based tourism destination in Indonesia.

Seagrass canopies are important components of the world’s coastal environments providing critical ecological services. Nearshore hydrodynamics, i.e., waves and currents, are essential in controlling the ecological processes across coastal environments. Seagrass meadows can impose more complex hydrodynamics processes by attenuating sea-swell waves and decreasing the impact of nearshore mean water level rise due to wave setup and Infragravity (IG) waves. Consequently, the seagrasses dissipate waves and reduce flows allowing sediments to settle and accrete the shorelines. However, despite their significant roles, knowledge of hydrodynamics in the Indonesian seagrass ecosystems is relatively limited compared to other coastal ecosystems such as sandy beaches, mangroves, and coral reefs. This review highlights the dynamics of waves and currents, and their interaction with sediment transport and ecological processes, including biogeochemical and dispersal processes on the seagrass ecosystem contributing to the existing seagrass research in Indonesia. The associated literature is collected from scientific databases such as Scopus and Google Scholar that range between 1965 and 2021. The result showed that most of the research on hydrodynamic in seagrass ecosystems was carried out in temperate zones. Until recently, there have been limited publications discussing the interaction between the Indonesian (tropical) seagrass ecosystem and hydrodynamics parameters, even though the region has abundant seagrass species. Moreover, Indonesia is strongly influenced by various atmospheric-oceanic forcing, including the Asian monsoon affecting the dynamic of the coastal area with seagrass ecosystems. At a canopy scale, the correlation between the nearshore (tropical) hydrodynamics and ecological processes in the system is yet to be explored. Considering the potential benefit of seagrasses to coastal ecosystems, developing future research in hydrodynamics across the ecosystem is critical to overcoming the knowledge gaps in Indonesia. The knowledge gained could support the Indonesian seagrass ecosystem services and their resilience to potential hazards and climate change.

Seagrasses provide diverse ecosystem services that support communities, yet, they are among the most threatened marine habitats. Efforts to conserve and sustainably manage seagrasses are increasing, particularly amidst the era of climate change, in which they play a critical role. However, these activities often received less attention or were slow in gaining momentum partly due to a lack of societal recognition of seagrasses and their importance. Thus, in this study, we collected community perceptions of seagrass ecosystem services and threats from 391 respondents in Karimunjawa National Park (KNP), a nationally declared protected area in Indonesia. We aim to provide insights on people's recognition of seagrasses from a local scale with strict protection measures. Overall, respondents showed varying perceptions of seagrass ecosystem services, with provisioning services more highly perceived than regulating services. The perceived level of threats was inconclusive, though, reclamation along shorelines received higher rates (leaning toward most damaging) than other threats such as natural disasters and illegal fishing activities. Sociodemographic attributes of respondents were found to influence their perceptions, with occupation as the most pronounced driving factor. The variations observed in seagrass perceptions suggest that there is a need to strengthen and/or enhance seagrass awareness and education campaigns, which is in line with the increasing demand that public perceptions matter for the conservation and sustainable management of seagrass ecosystems. We presented here the use and insights of community perceptions for seagrass blue carbon conservation in KNP, and consequently in Indonesia, where seagrass meadows are considered globally important carbon sinks.

ABSTRACT Tides and currents are essential factors that affect activities in estuary waters. The observation of tides and currents at the estuary of the Porong River is very important to support the development of Lusi Island, Sidoarjo Regency, East Java. The observation results in the form of tidal and current characteristics can be used to support the development of Lusi Island. Currently Lusi Island has been used as ecotourism to improve the economy of the people around the coast. This study aims to determine the characteristics of the tides and current velocity to support the development of Lusi Island. Analysis of the observed data was carried out to get an overview of the hydrodynamic characteristic at the study site. The results showed that the tidal range was 2.053 m and the average current speed was 0.25 m/s with a minimum current speed of 0 m/s and a maximum current speed of 0.86 m/s. The results of tidal analysis can be used as a elevation reference to construct buildings on Lusi Island, while the direction and speed of the currents can be used as initial information by the ship's captain as well as consideration for the location of the pier. The comparison model of tidal results obtained by the model that is closest to the measurement results is the Naotide model. The results of the most accurate model can be used to predict the height of the sea tides around Porong estuary. ABTSRAK Pasang surut dan arus merupakan faktor penting yang mempengaruhi aktifitas di suatu perairan muara. Observasi pasang surut dan arus di muara Sungai Porong sangat penting dilakukan untuk mendukung pengembangan Pulau Lusi, Kabupaten Sidoarjo, Jawa Timur. Hasil observasi berupa karakteristik pasang surut dan arus dapat dimanfaatkan untuk mendukung pengembangan Pulau Lusi. Saat ini Pulau Lusi sudah dimanfaatkan sebagai ekowisata guna meningkatkan ekonomi masyarakat sekitar pesisir. Penelitian ini bertujuan untuk mengetahui karakteristik pasang surut dan kecepatan arus yang dapat dimanfaatkan untuk mendukung pengembangan Pulau Lusi. Analisa data hasil observasi dilakukan untuk mendapatkan gambaran karakteristik hidrodinamika di lokasi penelitian. Hasil penelitian menunjukkan tunggang pasang surut sebesar 2,053 m dan kecepatan arus rata-rata 0,25 m/detik dengan kecepatan arus minimum 0 m/detik serta kecepatan arus maksimum 0,86 m/detik. Hasil analisa pasang surut dapat dimanfaatkan sebagai referensi pada perencanaan elevasi bangunan di Pulau Lusi, sedangkan arah dan kecepatan arus dapat dimanfaatkan sebagai informasi awal oleh nahkoda kapal serta pertimbangan penempatan dermaga yang akan dibangun. Hasil perbandingan model pasang surut diperoleh hasil model yang paling mendekati hasil pengukuran adalah model Naotide. Hasil model yang paling akurat dapat dimanfaatkan untuk prediksi elevasi pasang surut di sekitar muara Porong.

The global operational oceanography services provide freely accessible wave data. This research aims to use ERAS and CMEMS reanalysis to study the characteristics of the height, period, and direction of waves in the Java Sea. Such wave information plays an important role in coastal protection, shipping safety, and fishing activities on the northern coast of Java. The datasets are analyzed from 1993-2019 to obtain the extreme wave height, variability in wave height and direction, also wave propagation. An extreme wave height of 1.6 meters was obtained at the 95th percentile, and an extreme wave height of more than 3 meters was obtained during the 100-year statistical return period. The height and direction of the waves follow the seasonal wind variability. Wave mainly comes from the west during the northeast monsoon and in the reverse direction during the southeast monsoon. Swell propagation is detected from the two-dimensional spectrum. The primary swell comes from the South China Sea, but the Indian Ocean swell also enters the sea off West Java through the Sunda Strait.

Seagrasses offer diverse ecosystem services, yet, they are among the most threatened ecosystems. When degraded or destroyed, their services are lost or reduced in the process, affecting, for instance, local communities directly dependent on their livelihood provision. The Intergovernmental Panel on Climate Change (IPCC) reported that climate change is projected to worsen over time; thus, there is an urgent need for mitigation strategies in practice and also in the longer term. This work aims to provide an alternative perspective of seagrass restoration as a nature based solution (NbS) on a global scale, yet, giving an emphasis on tropical regions such as Indonesia. We focused on seagrass restorations which are not yet well established in comparison with other restoration programs (e.g., mangroves) despite their critical roles. We present in this work how restoring seagrass meadows fits the global standard of NbS published by the International Union for Conservation of Nature (IUCN). The results of this study can serve as a basis for promoting seagrass restorations as NbS against climate change particularly in countries with a wide extent of seagrass coverage.

ABSTRAK Kajian pasang surut dan arus sangat diperlukan untuk mendukung rencana pengembangan pelabuhan terintegrasi di muara Satui, Kalimantan Selatan yang saat ini sudah aktif beroperasi untuk alur lintas berbagai komoditas ekonomi penting. Pada kajian ini, karakteristik pasang surut dan kecepatan arus diperoleh dari observasi lapangan dengan alat pencatat arus yang dipasang di muara Satui dan data sekunder yang dikumpulkan dari beberapa sumber. Hasil kajian menunjukkan tunggang pasang surut sebesar 1,86 meter, dengan kecepatan arus berkisar ~0-0,47 m/detik (rata–rata kecepatan arus 0,12 cm/detik) yang dipengaruhi oleh debit air dari sungai Satui. Hasil kajian menunjukkan pasang surut dan arus di sekitar perairan muara Satui sesuai untuk kepentingan pelabuhan. Kata kunci: Pasang Surut, Arus, Muara Satui, Pelabuhan ABSTRACT The study of tide and ocean currents is very useful to support the plan to develop an integrated port area at Satui estuary, South Kalimantan which currently is being operated for transporting high value commodities. In this study, the characteristic of tides and currents was obtained from a field measuring campaign with a current profiler installed in Satui estuary and secondary data from various resources. The study showed the tide range was 1.86 m, with current velocity ranging ~0-0.47 m/s (average of 0.12 m/s) that was influenced by the flow of Satui river. The result exhibited the tides and currents within Satui eastuary was suitable for ports Keywords: Tides, Current, Muara Satui, Harbor

Rencana pengembangan suatu kawasan estuari untuk pelabuhan perlu memperhitungkan kondisi awal lingkungan karena daerah pelabuhan sangat rentan terhadap cemaran lingkungan akibat beragam aktivitas yang dilakukan. Studi ini bertujuan untuk mengetahui kualitas lingkungan perairan Muara Satui, Tanah Bumbu, Kalimantan Selatan yang potensial untuk dikembangkan sebagai kawasan kegiatan pelabuhan terpadu. Kualitas fisika, kimia dan biologi air hasil pengamatan dibandingkan dengan standar baku mutu air laut yang ditetapkan oleh Kementrian Lingkungan Hidup Indonesia. Selanjutnya, hasil pengamatan dianalisa lebih lanjut dengan Indeks Kualitas Air (IKA) untuk mengetahui gambaran umum kualitas perairan. Hasil analisa menunjukkan perairan muara Satui mempunyai kualitas perairan yang sangat bagus dengan parameter fisika (seperti salinitas 14 ppt, suhu 28°C), kimia (seperti DO 4,9 mg/l, dan BOD 5,41 mg/l), dan biologi (yaitu plankton dengan Indeks Dominansi Simpson 0,20-0,27) masih dalam kisaran standar baku mutu air laut untuk pelabuhan. Dari nilai IKA dengan kisaran 0,001 sampai 6,5 untuk berbagai parameter yang dianalisa, dapat disimpulkan bahwa perairan masih dalam kondisi yang sangat bagus. Hal tersebut mengindikasikan perairan tersebut layak untuk dijadikan kawasan pengembangan pelabuhan.

The estuary of Porong River Sidoarjo receives heavy pressure from a mud volcano eruption that is diverted into the Porong river to prevent wider destruction on the populated area. Due to massive mud discharge, over sedimentation on the estuary of Porong River potentially modifies the pattern of nearshore circulation. This paper investigated the patterns of nearshore circulation within the Porong estuary through observations and numerical models to understand the dynamics of coastal circulation under various seasons. The result showed the influence of astronomic water level variations (range of 2.1 m) and river discharge (average of 33 m/s) to the circulation patterns within the estuary. Further analysis showed the monsoonal variations did not significantly alter the nearshore patterns.

Pengetahuan karakteristik gelombang diperlukan dalam rangka mitigasi dan management pesisir. Kepulauan seribu merupakan kepulauan yang terletak diperairan laut Jawa dimana sebagian besar merupakan wilayah adminstrasi Provinsi DKI Jakarta. Sumberdaya laut yang beraneka ragam dan jumlah penduduk hampir 30 ribu orang menjadikan kegiatan kelautan dan Perikanan di Kepulauan Seribu memiliki nilai ekonomis penting bagi provinsi tersebut. Studi ini mengkaji karakteristik gelombang dan potensi gelombang ekstrim pada perairan di sekitar Kepulauan Seribu berdasar data gelombang tahun 2010-2020 ERA 5 serta mendiskusikan pemanfaatannya untuk bidang kelautan dan perikanan. Hasil analisa menunjukkan perairan kepulauan seribu tergolong tenang dengan tinggi gelombang signifkan rata-rata di lokasi penelitian sebesar 0,5 m dengan periode pendek berkisar 5 detik yang dominan dari arah Barat. Analisa Gumbel menunjukkan dalam jangka waktu yang panjang, terdapat kemungkinan gelombang besar lebih dari 2 meter. Prediksi gelombang ekstrim diperlukan untuk kepentingan mitigasi bencana pesisir seperti rob serta sebagai input dalam perhitungan bangunan pantai di Kepulauan Seribu. Disamping itu, desain dan penempatan kegiatan budidaya sangat membutuhkan informasi tersebut

The non-hydrostatic wave-flow model SWASH was used to investigate the hydrodynamic processes at a reef fringed pocket beach in southwestern Australia (Gnarabup Beach). Gnarabup Beach is a ~1.5 km long beach with highly variable bathymetry that is bounded by rocky headlands. The site is also exposed to large waves from the Southern Ocean. The model performance was evaluated using observations collected during a field program measuring waves, currents and water levels between June and July 2017. Modeled sea-swell wave heights (periods 5–25 s), infragravity wave heights (periods 25–600 s), and wave-induced setup exhibited moderate to good agreement with the observations throughout the model domain. The mean currents, which were highly-spatially variable across the study site, were less accurately predicted at most sites. Model agreement with the observations tended to be the worst in the areas with the most uncertain bathymetry (i.e., areas where high resolution survey data was not available). The nearshore sea-swell wave heights, infragravity wave heights and setup were strongly modulated by the offshore waves. The headlands and offshore reefs also had a strong impact on the hydrodynamics within the lagoon (bordered by the reefs) by dissipating much of the offshore sea-swell wave energy and modifying the pattern of the nearshore flows (magnitude and direction). Wave breaking on the reef platforms drove strong onshore directed mean currents over the reefs, resulting in off-shore flow through channels between the reefs and headlands where water exchanges from the lagoon to ocean. Our results demonstrate that the SWASH model is able to produce realistic predictions of the hydrodynamic processes within bathymetrically-complex nearshore systems.