Java Waters Research Articles

Genetic Diversity and Population Structure of Amphidromous Goby (Stiphodon semoni) in Western Part of Southern Java Waters

Graphical Abstract Research Highlight The genetic diversity of Stiphodon semoni is high. All populations have high haplotype diversity except for Cimaja. No genetic structure is observed within the populations of semoni. The population of semoni has undergone demographic expansion. Cibareno River has the potential to be a protected area. Abstract Fishing activities negatively impact fish populations, potentially causing a decline in fish stocks. Nevertheless, ensuring diversity and connectivity among populations can mitigate these adverse effects. To evaluate the connectivity of river mouths in the western part of Southern Java waters, we sequenced forty Stiphodon semoni individuals from five populations using mitochondrial cytochrome oxidase subunit 1 as molecular markers. The study revealed that S. semoni populations showed high diversity (0.821), with the population in Cimaja displaying the lowest diversity (0.464). Furthermore, the result of the analysis of molecular variance was a Fst value of 0.0630 with a p-value of 0.22. These results along with the result of the haplotype network indicated no significant genetic differences among these populations. This implies that the river mouths in the western part of Southern Java waters are interconnected. The distribution of mismatches showed a single peak, indicating that the populations have undergone demographic expansion. This information could be valuable for the conservation and management of S. semoni in the western part of the Southern Java waters.

Ichthyoplankton Biodiversity in the Indonesian Fisheries Management Area-573 in 2015

Abstract Studying ichthyoplankton is crucial for understanding the impact of fish larvae mortality on the recruitment of adult fish and fishing resources. Fish larvae samples were collected in the southern waters of Java using the Baruna Jaya IV research vessel in September - October 2015. Fish larvae were collected using bongo-net and oceanographic data were collected using Conductivity Temperature Depth (CTD) are Temperature and salinity and chlorophyll-a using Aqua MODIS satellite L3 at 36 stations. The results showed the range of fish larvae abundance was 0 - 2,074 ind/1000 m3 with an average of 174 ind/1000 m3. The fish eggs were found with an abundance of 0 - 1,601 eggs/1000 m3. and an average of 213 eggs/1000 m3. The composition of fish larvae recorded 22 families, there were 5 dominant families namely Scombridae (28.60%), Bregmacerotidae (22.96%), Carangidae (7.93%), Blennidae (7.52%), and Gobiidae (7.52%). The diversity of fish larvae was most prevalent at station 28 (SST 26.7 0C; SSS 34.4 PSU; and CHL-a 0.43 mg/m3) and station 36 (SST 27.4 0C; SSS 34.4 PSU) each found 9 families. The abundance of fish larvae was mostly found at stasion 11 had SST 23.50 0C; SSS 34.56 PSU; and CHL-a 0.33 mg/m3 with the dominance of the family Bregmacerotidae. Scombridae was mostly found at stasion 22 with sea surface temperature (SST) 26.52 0C; sea surface salinity (SSS) 34.28 PSU; and sea surface chlorophyll-a (CHL-a) 0.41 mg/m3 which is in the southern waters of Lombok.

Water mass exchange in triangle seas of the Java-Makassar-Flores (JMF): A modeling study

The ocean dynamics of the marginal seas in the Java-Makassar-Flores (JMF) Triangle seas facilitates the seasonal exchange of water masses between Java, Makassar, and Flores, which influences the occurrence of small pelagic fish. This research investigates seasonal fluctuations in sea currents, seawater temperature, salinity, and phytoplankton primary production (PPN and PPD) based on validated model output datasets from NEMO and PISCES from the INDESO simulation (2008–2015). The model demonstrated seasonal exchanges of the top 50 m of water masses in the area, where the eastward monsoon current transported freshwater (salinity<31 psμ) from the Java Sea to southern Makassar and Flores. This northwest monsoon produced a much fresher water in the southern region of Makassar and western region of Flores. During the southeast monsoon, the surface component of the Makassar throughflow, which transports saline water (salinity >34 PSU) into the Java Sea, pushes fresh Java waters westward. Seasonal salinity changes and PPN/PPD in the shelf region of southern Kalimantan correlated with substantial small pelagic fishing.

Essential Elements in Muscle Tissue of Rhizoprionodon acutus and Sphyrna lewini from West Java Waters

Essential Elements in Muscle Tissue of Rhizoprionodon acutus and Sphyrna lewini from West Java Waters

Dominant species of squid in the waters of Western Kalimantan and Northern Java identified by DNA barcoding method

Squid resources in Indonesia have high economic value, and their exploitation tended to increase due to declining fish resources in many waters. Previous research mentioned that 21 squid species were identified in Indonesian waters. However, many researchers argued that the identification of cephalopod morphology, especially squids, was challenging, and that is why supporting methods were needed, one of which was DNA analysis. The study aimed to determine the type and distribution of squid in the western waters of Kalimantan and northern Java using the DNA barcoding method on the COI gene. Squid samples were collected from six locations, consisting of Tanjung Pinang, Bangka Belitung (Babel), Kalimantan Barat (Kalbar), Muara Angke, Pekalongan, and Lamongan. The analysis results showed that Uroteuthis chinensis was present in all sampling locations except Tanjung Pinang, where Uroteuthis edulis and U. sibogae were found. The results of this study are very important in the management of squid resources because they can contribute to the sustainable management of marine resources and the maintenance of the sustainability of marine ecosystems.

Kinship relationship of Uroteuthis chinensis in the waters of western Kalimantan and northern Java based on morphometric characters and genetic structure

Uroteuthis chinensis was a squid species with a wide distribution and rapid reproduction. It was commonly found in the waters of western Kalimantan and northern Java, which were the highest squid fishing grounds in Indonesia. Exploitation of U. chinensis in these waters was intensive and increasing, which might have affected the sustainability of U. chinensis squid resources. Therefore, proper and responsible management was needed to maintain the sustainability of this squid resource. For exploitation to be sustainable and optimal, management based on stock units of the managed resources was required. Therefore, information was needed on the stock units of U. chinensis squid in the western waters of Kalimantan and northern Java. Currently, the Indonesian government has separated the management of these two interconnected waters. The method used was to analyze 12 morphometric characters and genetic structures with COI and Rhodopsin markers. Sampling locations included the Sungailiat and Pontianak, for the waters of western Kalimantan, Jakarta, Pekalongan, and Lamongan for the waters of northern Java. Morphometric data were analyzed using Principal Component Analysis (PCA) and Discriminant Analysis (DA) approaches. Genetic analysis (COI and Rhodopsin) included genetic diversity, AMOVA, and haplotype distribution. The results of the morphometric analysis showed that the 12 morphometric size characters in this study showed a close relationship between the five U. chinensis sample populations. Genetic variation between populations and FST values on COI and Rhodopsin showed very low values; P-values also showed results that were not significantly different between populations. The haplotype distribution of both COI and Rhodopsin showed almost the same composition in both observed waters. The results of these analyses suggested that U. chinensis species in both waters showed indications of connectivity and close kinship or could be regarded as a single stock. Therefore, collaborative management across fisheries management areas in both waters (western Kalimantan and northern Java) was required.

Influence of Anomalous Upwelling on the Water Mass of South Java during Two Positive Indian Ocean Dipole in 2015 and 2019

Upwelling is a phenomenon that often occurs in the ocean. Upwelling can be interpreted as the process of rising sea water masses from below the surface to the surface due to the vacancy of sea water masses at the surface. The upwelling phenomenon will cause many anomalies that have a direct impact on ocean dynamics, one of which is the dynamics that occur in the waters south of Java. The formation of the coastal upwelling phenomenon in the waters south of Java in 2015 and 2019 was the cause of the active Positive IOD in both years. By carrying out time series analysis and spatial data visualization processes as well as correlation methods to determine the relationship between parameters, this research aims to discuss and find out about the influence of coastal upwelling dynamics on the waters of southern Java in 2015 and 2019. The results obtained from this research show that the coastal upwelling phenomenon formed in 2015 and 2019 along the waters of southern Java resulted anomalies in dynamic patterns in the form of decreasing sea surface temperatures and increasing chlorophyll-a concentrations

DNA Barcoding of Anchovy in Tuban Regency as Database of Indonesian Marine Genetic Diversity

Anchovy is the main catch and the primary consumption of coastal communities in Indonesia, and its production shows an increase of more than 10% in 2021. Tuban district, in East Java, Indonesia is part of the WPP 712 (Wilayah Pengelolaan Perikanan or Fisheries Management Area) and highly produces anchovies’ fisheries. Anchovy has a small size, making it difficult to identify morphologically. This study aimed to genetically identify anchovy samples obtained from North Java (Tuban) waters. Molecular identification was conducted by utilizing Cytochrome Oxidase Subunit I (COI) gene using jg-HCO and jg-LCO primers. This study observed 12 individual samples with 623 base pair sequence length. Five species were obtained, namely four species of anchovies (Encrasicholina heteroloba, Encrasicholina punctifer, Stolephorus waitei, and Stolephorus insularis) and one species of sardines (Dussumieria elopsoides) with 99.84-100% similarity to NCBI sequences data. Anchovies typically have a streamlined body with a slightly compressed shape. Anchovies have cycloid scales, which are smooth-edged and relatively small, ranging from a few centimeters to around 20 centimeters in length. Some of the genus from the Anchovy group are Encrasicholina and Stolephorus. The phylogenetic tree reconstruction leads into four clades with a genetic distance between clades of 17,9-24,5 %. This research provides methods and data on the genetic diversity of anchovies taxa caught in Tuban, East Java. The findings are expected to support promoting new standards for healthier and more sustainable anchovy stocks in the country. Overall, this study contributes to providing valuable insights for fisheries management and conservation efforts in Indonesia.

Application of Sustainability Index of Tidal River Management (SITRM) in the Lower Ganges–Brahmaputra–Meghna Delta

The sustainability index (SI) is a relatively new concept for measuring the performance of water resource systems over long time periods. The purpose of its definition is to provide an indication of the integral behavior of the system with regard to possible undesired consequences if a misbalance in available and required waters occurs. Therefore, the tidal river management (TRM) approach has been implemented for the past three decades (from 1990 to 2020) within the polder system in Southwest Bangladesh to achieve water sustainability. TRM plan and watershed management plan (WMP) have commonalities as both are aimed at ensuring the sustainable use of watershed resources with the management of land, water, and the wider ecosystem of the watershed in an integrated way. The TRM plan focuses mostly on coastal regions, whereas the WMP focuses on both coastal and non-coastal regions. According to this, the aim of this study was to explore the application of the sustainability index of tidal river management (SITRM) in measuring the sustainability of tidal river management in the coastal area of the Lower Ganges–Brahmaputra–Meghna (GBM) delta. In order to quantify the sustainability of tidal river management, this research first provided the components and indicators of SITRM for the coastal region. The study follows a 5-point Likert scale for opinion survey of key informants and comprises households’ survey of farmers. In addition, it includes Landsat satellite images from Earth Explorer of the United States Geological Survey (USGS) and direct field observation to collect information regarding the indicators of SITRM. The study measures the index value of SITRM for identifying the water sustainability of Beel East Khukshia-TRM. The index value was 71.8 out of 100, showing good tidal river management for the Hari–Teka–Bhadra catchment. To achieve water sustainability and aid stakeholders and water managers in decision making, it may be possible to include the SITRM framework in tidal river management projects. In addition, the SITRM is more capable of facing drainage congestion, waterlogging, and climate change issues than watershed sustainability index (WSI), Canadian water sustainability index (CWSI), West Java water sustainability index (WJWSI), and water poverty index (WPI). Therefore, water professionals and policymakers can apply SITRM to assess the resilience of specific TRM schemes for greater sustainability in different coastal regions of the world.

Tidal Characteristics in Southern Waters of Java - Indonesia

Detailed information regarding tidal characteristics in Indonesian waters is not yet available evenly, including in the southern waters of Java. Tides are one of the most essential hydro-oceanographic parameters in water dynamics. Therefore, this study aims to analyze the characteristics of the tides in the southern waters of Java, starting from Banten Regency in West Java to Malang Regency in East Java. Tidal data with measurement intervals every one hour were collected from December 23, 2022, to January 20, 2023, from ten tide stations with details: 1 station each in Banten and Central Java, three stations each in West Java and East Java, as well as two stations in Yogyakarta. Data from each station is then processed using the Admiralty method to obtain tidal harmonic constant and Formzahl values. Based on the tidal harmonic constants' amplitude and the Formzahl values (F), the tidal type in the southern waters of Java is a mixed tide prevailing semi-diurnal (F ranged from 0.64 - 1.34). The tidal range in the southern waters of Java ranges from 178 - 332 cm. In more detail, Banten and Pelabuhan Ratu waters are classified as micro tides (the tidal range is 178 and 182 cm, respectively). At the same time, the rest are categorized as meso tides (tide range between 200 - 400 cm).Keywords: Tidal Type, Admiralty, Formzahl, Tidal Range, Indian Ocean

Integration of tuna fishery data collection in the Southern Waters of Java (FMA-573)

Fishing operational data is the key to making fisheries management policies. Without this data, policymakers could only speculate on current field conditions; hence their decisions are not solutions to issues and problems in fisheries management and are even difficult to implement. Currently, the government encourages data collection on fishing operations through three schemes, namely data collection on the results of fish unloading at fishing ports, independent data reported by fishermen (fishing logbook), and data on monitoring results on fishing vessels by observers on board. Integrating such data is one solution to obtain sufficient operational data for fishing in quantity and quality. This study uses data on tuna catches from the three data collection schemes to tuna longline in the Southern Waters of Java, FMA 573. This study aims to analyze the differences between the established fisheries data collection standards with the existing conditions and the parties’ involvement in data collection activities. The analysis results show differences in data collection activities in existing conditions with the existing standards, affecting the completeness and quality of the resulting data. The integration of the three data is complementary and significantly impacts the quality of fishery data produced.

Wave climate characteristics and effects of tropical cyclones on high wave occurrences in Indonesian waters: Strengthening sea transportation safety management

Tropical cyclones can cause bad weather and high waves that can endanger maritime activities, especially in the waters of Indonesia, which is a maritime country. Understanding ocean wave climate characteristics and the effect of Tropical Cyclones (TCs) on high wave occurrences is important, particularly to ensure the safety of fisheries activities in Indonesian seas. We aim to do so by focusing on Indonesia's 11 Fisheries Management Areas (IFMAs) using descriptive and inferential statistics. Wind and wave data were taken from the European Center for Medium-Range Weather Forecast (ECMWF), namely ECMWF Reanalysis v5 (ERA5) within the range of 42 years (1979–2020), whereas the TC data were from the International Best Track Archive for Climate Stewardship (IBTrACS). We found that significant wave heights (SWHs) in the inner seas are strongly related to monsoonal wind fields. The maximum SWH occurred in northern Indonesian seas during December–February (DJF), while occurring in southern and inner seas between June–August (JJA). The highest extreme SWH and probability of exceedance (PE) for SWH >2 m were found in IFMAs facing the open ocean, such as Malacca Strait, Western Sumatra waters, Southern Java waters, Natuna Sea, Sulawesi Sea, and Northern Papua waters. We found that TCs activity in adjacent Indonesian waters could increase anomalous SWH occurrences. Positive SWH anomalies ranged from 0.1 to 0.4 m and varied depending on TC location and season. TC that forms in the following areas increase the PE for SWH >2 m: (1) Bay of Bengal: Western Sumatra waters (March–May, MAM) around 20%; (2) Western Pacific Ocean: Northern Papua waters (DJF) around 5%; (3) Northeastern Indian Ocean: Western Sumatra waters (DJF) about 3%; and (4) Western and Northern Australian waters: Southern Java waters (DJF) about 20%. The results of this study can serve as an early assessment for investigating wave climate characteristics and identifying the areas in Indonesian waters that are most susceptible to the impact of TCs, particularly in IFMAs. These findings hold significant value for managers and policy authorities, such as the Ministry of Transportation and the Ministry of Marine Affairs and Fisheries of the Republic of Indonesia. They can utilize this information to develop measures aimed at reducing vulnerabilities among marine resource users, specifically fishers, and improving fishing vessel safety. Additionally, these findings can be utilized to enhance advance warnings and forecasts, enabling marine managers to implement strategies that minimize the impact of extreme events and increase resilience in the face of ocean and coastal disasters.

Analysis of the effect of ENSO and IOD on the productivity of yellowfin tuna (Thunnus albacares) in the South Indian Ocean, East Java, Indonesia

Abstract. Sambah AB, Noor’izzah A, Intyas CA, Widhiyanuriyawan D, Affandy DP, Wijaya A. 2023. Analysis of the effect of ENSO and IOD on the productivity of yellowfin tuna (Thunnus albacares) in the South Indian Ocean, East Java, Indonesia. Biodiversitas 24: 2689-2700. Yellowfin tuna (Thunnus albacares) is one of the fish that migrates through the Indian Ocean and is primarily caught in the south Java waters which are directly adjacent to the Indian Ocean. Fish abundance and migration are influenced by oceanographic factors, including climatic factors which affect annual and interannual variations, such as the Indian Ocean Dipole (IOD) and the El Nino Southern Oscillation (ENSO). This study aimed to determine the effect of climate anomalies on the productivity of yellowfin tuna in the Indian Ocean south of East Java, Indonesia. Data collection was carried out at Coastal Fishing Port of Pondokdadap East Java, involving 58 respondents consisting of fishermen with yellowfin tuna catches. The boundaries of the research area are at coordinates 110.9°-114.5° East Longitude and 8°-11° South Latitude. The data used in the analysis consisted of Sea Surface Temperature (SST) data, chlorophyll-a data, Nino 3.4 data, Dipole Mode Index (DMI) data, and yellowfin tuna catch data for the year 2017-2021. The results showed that of the fifteen GAM models, the combination of variables that most affected fish productivity was the distribution of chlorophyll-a and the ENSO phenomenon with values ??of AIC (1503.33) and DE (64.30%). Pearson correlation analysis showed that the IOD phenomenon was influenced by SST and chlorophyll-a, while SST and chlorophyll-a did not significantly influence the ENSO phenomenon. These results indicated that the phenomenon of climate anomalies and the oceanographic conditions in the waters indirectly affect fish productivity through the food chain process.

Reproductive biology of Indian mackerel, Rastrelliger kanagurta (Cuvier, 1816) in the southern waters of West Java (FMA 573)

Indian mackerel is a small pelagic fish with important economic value in Java Island. This study aims to analyze the reproductive characteristics and determine management recommendations for the Indian mackerel in the southern waters of West Java. Fish monthly sampling collection was conducted at three fish landing ports: PPI Ciwaru, PPN Palabuhanratu, and PPI Binuangeun from July to December 2022. A total of 1,038 fish samples, comprised of 582 males and 456 females, were examined. The sex ratio was unbalanced, with a value of 1:0.79. Gonadosomatic indexes ranged from 0.19-0.95 and 0.45-3.41 for males and females, respectively. The fish fecundity ranged from 27,027 to 87,837 eggs. The Indian mackerel is predicted to spawn every month, with a peak season in August, and performs a total spawner pattern. The Indian mackerel reached the size of the first maturity gonad at 198.5 mm and 197 mm for males and females, respectively. Management strategies for Indian mackerel in the southern waters of West Java include setting the catch size above the first mature gonad size (197 mm), the mesh size of gillnets above 1.5 inches, and limiting fishing activities during the spawning season (July, August, and September).

Reproductive aspects of the Japanese threadfin bream, Nemipterus japonicus (Bloch, 1791) in the Southern Java waters (FMA-RI 573)

This study describes the reproductive biology of the Japanese threadfin bream, Nemipterus japonicus (Bloch, 1791) captured from the Southern Java Waters (FMA-RI 573). Fish monthly sampling collection was conducted from July to December 2022 at three fish landing ports: PPI Ciwaru, PPN Palabuhanratu, and PPI Binuangeun. Overall, 951 individuals consisting of 469 males (49.32%) and 482 females (50.68%), with a size range of 92-300 mm and a weight range of 10–344 g were collected. The sex ratio is balanced (1:1.10), with fecundity ranging from 10,079 to 82,650 eggs. The length at first maturity is 146 mm for males and 141 mm for females. The Japanese threadfin bream is a total spawner. Spawning occurs throughout the sampling period, with a peak in October-November. The length-based spawning potential ratio (LBSPR) measures the sustainability of fish stocks, indicating that Japanese threadfin bream in southern Java is in an overexploited condition.

Potential Distribution of Skipjack Tuna Using MODIS Satellite Imagery in The Southern Waters of West Java - Banten

The West Java southern waters - Banten is among the skipjack tuna Katsiuwonus Pelamis distribution areas. It is well known that the skipjack tuna potential distribution is influenced by the environmental circumstances of the waters. This study was performed to establish the potential distribution of skipjack tuna in the West Java southern waters– Banten to support the potential management program of marine fishery resources. The data used consisted of skipjack tuna catch position, sea surface temperature, and chlorophyll-a concentrations from June 2019 to August 2019. Descriptive analysis and maximum entropy (maxent) model were applied to analyze skipjack tuna’s potential distribution. The results revealed that the potential area of skipjack tuna is scattered in parts of the southern waters of West Java - Banten, with a validation test of the model performance of 0.92 (excellent).

Evolution of Subsurface Temperatures in West Sumatra - Southern Java Waters During 2010–2014 Indian Ocean Dipole Events

The temperature anomaly formation in the West Sumatra and South Java Waters plays an important role in the formation of the Indian Ocean Dipole (IOD). There have not been many detailed studies on the evolution of temperature anomalies in the subsurface layers in the area during the IOD events. In this study, temperature data from the HYCOM were used to examine the evolution of temperature anomalies on the surface and subsurface in the event of negative IOD (nIOD) 2010 and positive IOD (pIOD) 2012). The analysis was done using a cross-section plot and a Hovmöller diagram. It has shown that in the negative IOD 2010, a positive temperature anomaly in the subsurface layer was started four months earlier than the surface layer and ended six months after the IOD event. In contrast to positive IOD 2012, a negative temperature anomaly formed in the surface layer seven months earlier, and then move to the deeper layer coincide with the onset of the positive IOD event. The negative anomaly in both layers was simultaneously over two months after the positive IOD event over. The La-Niña phase that coincides with the positive or negative IOD event, influences the process of forming temperature anomalies in the subsurface layer, which in this case supports (inhibits) the formation of positive (negative) temperature anomalies in negative (positive) IOD event. The temperature anomaly in the subsurface layer can be an alternative indicator in identifying and predicting IOD events.

Leading Condition Of Small Pelagic Resources Based On Data In The State Fisheries Management Area Of The Republic Of Indonesia (Wppnri) 712 And 573 Year 1990 - 2017 East Java Province For Sustainable Management

Pelagic fish resources have a very important role in regional economic development. The assumption that fish resources are common property so that everyone is free to catch (open access) is a problem with overfishing in East Java waters. The purpose of this study is to determine the superior commodity of small pelagic fish, the status of exploitation of superior fish resources and to compile a scenario of sustainable management of superior resources. The method in this research is quantitative descriptive method with data analysis used including Location Quotient (LQ), Schaefer (1954), Fox (1970), Walter Hilborn, and programming STELLA (System Thinking, Experimental Learning Laboratory with Animation). The research result of the superior species in the province in the south of East Java) is sardin, while the superior fish in the regency is s Rainbow runner. The status of fisheries at the level of superior fisheries exploitation in South East Java, the level of exploitation of ssrdin fish is 240% with the status of Depleted. Finally, the level of exploitation for s Rainbow runner fish is 689%, which means that they are included in depleted. The scenario of sustainable management of pelagic fisheries for the next 10 years, namely 2018 - 2027 for lemuru fish, the highest biomass reserves will be obtained in 2027, using a fixed effort allocation which has biomass reserves of 179% and the potential value of sustainable reserves of 8,438.48 tonnes. The results showed that the superior commodities of small pelagic fish in North East Java were mackerel fish. The superior fish commodity in the Regency / City is obtained by Finny scad fish. The level of exploitation for mackerel is 127% with the status of Over Exploited, and the level of exploitation for Finny scad is 131% with the status of Over Exploited. The scenario for the management of the superior mackerel commodity, the highest biomass reserve in 2027 is the allowable fishing effort allocation (fJTB) of 129%. Key Words: STELLA ,Superior commodity, Fishery status, Sustainable potential

The Effect of Local Forcing on Anomalously High Rainfall during Dry Season in Java, Indonesia

During the dry season (May to October) in Java, Indonesia, anomalously high rainfall is investigated using 37-year rainfall data from the Climate Hazards Group InfraRed Precipitation with Station data. The analysis focuses on the years having high rainfall during the dry season between 1982 and 2019. It is conducted using a combination of the presence and absence of La Niña, negative Indian Ocean Dipole Mode events, and other atmospheric/oceanic parameters, such as 2-m temperature, sea surface temperature, outgoing longwave radiation, 200 mb and 850 mb wind. The results show that the presence of both La Niña and negative Indian Ocean Dipole Mode events contributes around 39% to the high rainfall during the dry season, the presence of negative Indian Ocean Dipole Mode - 22%, the absence of both events - 22%, and the presence of La Niña - 17%. The dynamics of monsoon circulation anomaly (200 mb and 850 mb) in the southern Indian Ocean off the coast of Sumatra and Java also plays a role in the increased rainfall during the dry season in Java. This anomaly occurs due to a vortex in the southern equatorial Indian Ocean around 10⁰S, triggering the formation of double Inter-tropical Convergence Zones over the area north of the equator and the southern waters of Java. The increase in rainfall due to this local factor reaches a maximum and extends in June and October, which is associated with the strengthening of circulation anomalies in southern Java, both spatially and vertically (850 and 200 mb).

Eutrophication in a tropical estuary: Is it good or bad?

Coastal eutrophication is defined as the increase of rate of organic supply into an estuary. In the recent global discussion, eutrophication is seen as a negative situation, in fact, it has positive impacts such as increase in primary production which lead to the increase of fisheries production and hence, community income. This paper promotes a simple diagram called eutrophication-benefit curve which correlates between levels of eutrophication and its benefits to both ecological and economical aspects. In the beginning of eutrophication process, environment gets benefit from the increase of the nutritional state of the water which leads to the increase of primary production and fisheries production. This is obvious in the comparison between northern and southern coast waters of Java Island, showing a higher primary production and phytoplankton biomass and hence fisheries production in the northern coast waters of Java compared to those of the southern coast waters of Java. However, the rapid increase of eutrophication level of the northern coast waters of Java Island causes eutrophication negative effects such as oxygen depletion, algae bloom and disturbance of coral reef ecosystems. This paper shows the optimum level of eutrophication level that can give benefit to both ecological and social environment.