Muddy Sand Research Articles

Textural Characteristics and Depositional Environment of Ngrayong Sandstone (Middle Miocene) from Rembang Area, Northeast Java, Indonesia

Granulometric analysis of Ngrayong sandstone samples from Rembang area of NE Java (Indonesia) has been carried out to examine the textural characteristics and elucidate depositional environment. The result data from the grain size analysis indicates that the Ngrayong sediments are classified as sand or muddy sands. They are very fine- to medium-grained (phi values: 1.67 to 3.35), moderately- to well-sorted (standard deviation: 0.19 to 0.57), strongly fine-skewed to strongly coarse-skewed (skewness values: 4.82 to −5.97), and very platykurtic to very leptokurtic (kurtosis values: 0.36 to 2.41). Sandstone samples show unimodal grain size distribution. The sediments are interpreted to be transported in all three modes-traction, saltation and suspension, however, suspension and rolling are the major processes during transportation. Discriminant functions indicate diversity in the depositional environment for the sandstones. However, shallow marine is regarded as the dominant depositional environment. The preponderance of fine-grained sediments and lack of coarse sands suggest low to moderate energy conditions during deposition of Ngrayong sediments.

Analysis on Effective UAS Survey Conditions for Classification of Coastal Sediments

This study aims to introduce effective unmanned aerial system (UAS) survey conditions for coastal sediment classification, including muddy sand, sand, gravel, and shells in a tidal flat area. UAS images with resolutions ranging from 2 to 60 mm are used as an implication of survey altitudes. The UAS images are used for sediment classification using random forest (RF) and support vector machine (SVM) methods. The results showed that RF is more effective in sediment classification while the general accuracy pattern was similar. The accuracy decreased with lower spatial resolutions. Notably, there is a significant drop of accuracy with a resolution coarser than 40 mm. Considering the training data selection, classification accuracy, and survey efficiency, it is suggested that 40 mm UAS images would provide optimal condition with acceptable accuracy for coastal sediment classification using RF model. To gain higher accuracy, a lower flight altitude is required, which will elongate the survey time significantly. Given the fact that this study is the first approach to test various UAS survey conditions for coastal sediment classifications in a field condition; the methodology and findings of this study can serve as a guideline framework for future coastal UAS sediment mapping.

Suitability analysis of mangrove conversation areas in Mundu District, Cirebon Regency using Geographic Information Systems (GIS)

This study aims to analyze the suitability of mangrove conservation areas in the Mundu District, Cirebon Regency. In this study, we used Sentinel-2A satellite data obtained from ESA Copernicus’s web to analyze the normalized difference vegetation index (NDVI) of mangrove that will be used as a mangrove health indicator and several oceanographic characteristics to assess the suitability of mangrove conservation areas based on weighing-scores systems. All data were then analyzed using image processing combined with geographic information systems (GIS) tools available in the open-access QGIS software. Results show that the health of the mangrove based on vegetation index was in the range of 0.3–0.6. Mangroves in Mundu Region have consisted of two species, Avicennia marina, and Rhizophora apiculata. The substrate in this area is dominated by muddy sand with a pH value of 8 and an average salinity of 32 PSU. The tidal type in Mundu region has mixed semi-diurnal characteristics with an average tidal height of 1.22 m. Based on those parameters and NDVI analysis, the suitability rank for mangrove conservation areas can be classified as suitable with a total score in the ranges of 101-200.

Perbandingan Morfometrik dan Meristik Lamun Cymodoceae serrulata di Perairan Sanur dan Tanjung Benoa, Bali

Cymodoceae serrulata is a type of seagrass that has a slender and round-toothed shape on the tips of leaves that can live in a variety of substrates ranging from rocking to muddy sand. Morphometrics and meristic can describe the environmental conditions of living seagrasses which can be seen from leaf morphology, stem morphology, rhizoma morphology and root morphology. Morfometrics is a measurement to determine the quantitative morphology of an organism while meristic is a calculation of the number of parts of an organism. This research was conducted in January-April 2019 using a purposive sampling method at 8 observation stations in the waters of Sanur and Tanjung Benoa. Data were analyzed by sturges criteria and principal componen analysis. Based on the results of the study, leaf length ranged from 13.4-246.6 mm, leaf width ranged from 3-18.5 mm, stem length ranged from 1-130.3 mm, root length ranged from 10.1-134.1 mm, rhizoma length ranged from 10.1-78.8 mm, rhizoma diameter ranged from 1.2-3.73 mm, the diameter of the leaf stalk ranged from 1.11-3.63 mm and the number of leaves ranged from 2-5 strands. The principal component analysis showed that texture of the substrate (sand, dust, and clay) that most influences the morphometric-meristic seagrass Cymodoceae serrulata is the texture of dust and clay texture. Where the dust texture affects morphometrics-meristik such as the length of the leaf, leaf width, stem length, rhizoma length, root length and number of leaves. While of the stem diameter and rhizoma diameter and root length are influenced by clay texture.

The potential of the spiny lobster fishery in Aceh waters: A short review

The western-southern and northern coastal waters of Aceh are the potential fishing areas of spiny lobster, which faces the Indian Ocean and the Andaman Sea. Fishing gears that are widely used are lobster gill nets and hand-picking with compressors. In Indonesia, seven species of spiny lobsters are caught in these waters, including Panulirus homarus, P. penicillatus, P. versicolor, P. ornatus, P. polyphagus, P. longipes longipes, and P. longipes femoristiga. The habitat for spiny lobsters is spread from coral reefs, rock, sand, and muddy sand. Panulirus homarus is the most frequently caught species in these waters, followed by P. penicillatus and P. longipes. Panulirus homarus is mainly caught during the dry season (southwest wind) and high waves (May to July), where other lobster species experience a significant decrease in the catch. The stock of spiny lobster in Fisheries Management Area (FMA) 572 (including Aceh coastal waters) has been in an overfishing condition since 2008. Maximum sustainable yield (MSY) of spiny lobster in Aceh coastal waters part of Malacca Strait (FMA 571) is 188.60 tons.yr−1 with a total allowable catch (TAC) of 151.10 tons. yr−1. Furthermore, the MSY for Aceh coastal waters part of Indian Ocean is 292.09 tons.yr−1 with a TAC of 233.92 tons.yr−1. Spiny lobster fishing in Aceh coastal waters must ensure its use in the future, both ecologically, socially, and economically.

Facies Analysis and Sedimentary Architecture of Hybrid Event Beds in Submarine Lobes: Insights from the Crocker Fan, NW Borneo, Malaysia

Hybrid event beds represent the combined effect of multiple geological processes, which result in complex depositional geometries and distinct facies distribution in marine environments. Previous work on hybrid event beds highlights the classification, origin, and types of hybrid facies. However, in the present study, we discuss the development of hybrid event beds in submarine lobes with an emphasis on the analysis of proximal to distal, frontal to lateral relationships and evolution during lobe progradation. Detailed geological fieldwork was carried out in the classical deep-marine Late Paleogene Crocker Fan to understand the relationship between the character of hybrid bed facies and lobe architecture. The results indicate that hybrid facies of massive or structureless sandstone with mud clasts, clean to muddy sand, and chaotic muddy sand with oversized sand patch alternations (H1–H3) are well developed in proximal to medial lobes, while distal lobes mainly contain parallel to cross-laminated clean to muddy hybrid facies (H3–H5). Furthermore, lateral lobes have less vertical thickness of hybrid beds than frontal lobes. The development of hybrid beds takes place in the lower part of the thickening upward sequence of lobe progradation, while lobe retrogradation contains hybrid facies intervals in the upper part of stratigraphy. Hence, the development of hybrid beds in submarine lobe systems has a significant impact on the characterization of heterogeneities in deep-marine petroleum reservoirs at sub-seismic levels.

Diversifikasi Produk Olahan Buah Mangrove Dau (Bruguiera Gymnoorhiza) Untuk Cake Gulmerda Dan Sirup Dau Di Desa Maitara Utara Kota Tidore Kepulauan

Mangrove forests are biological resources found in coastal areas that have ecological and economic functions. Bruguiera gymnorrhiza is a type of mangrove that grows in the middle and back zones with a muddy sand substrate. The fruit can be used as a local food source, especially in coastal areas that have the potential of mangrove forests, but of course must pay attention to the sustainability of the mangrove ecosystem. This PKM aims to apply the technology of processing the Bruguiera gymnorrhiza mangrove fruit for gulmerda cake and syrup which has a high selling value. The methods used in the Community Partnership Program (PKM) activities are lectures, practice, hedonic testing and mentoring. The results of PKM have increased public knowledge in utilizing raw materials that are around their environment to be processed into products that have a selling value, motivating people to be more independent and confident in developing businesses to improve community welfare, organoleptic testing, Cake gulmerda products are products that have higher score. The formation of the entrepreneurial group "Let's Feel Creative" in the context of the sustainability of training activities.Keywords: Diversification, processed mangrove fruit, gulmerda cake, Dau syrup, North Maitara

FIRST REPORT: EXISTENCE OF ALPHEID SHRIMP (Alpheus lobidens De Haan 1849) IN MANGROVE ECOSYSTEM OF KUALA LANGSA, ACEH, INDONESIA

AbstractThe existence of alpheid shrimp species in Indonesia is not too much found in the latest scientific publications. Alpheid shrimp species can be used as an indicator to assess the quality of the environment in mangrove areas. The discovery of shrimp species from the Alpheid group adds to the list of biodiversity in the mangrove area of Kuala Langsa. Biodiversity of a high number of species in this group of shrimp is usually found in mangrove areas with muddy sand beaches. This is because, this type of shrimp has a habit of living in muddy areas. The living zone of this type of shrimp is almost the same location as the type of crab that is wrapped like the Scylla serrata group. Mangrove area kuala langsa although it has mangrove biodiversity that is relatively high. Kuala Langsa mangrove forests are dominated by the Rhizoporaceae group, which is a type of vegetation that is effective as a sediment trap from the direction of the river estuary while holding abrasion from the direction of the sea. In the current year there is also a condition of decrease in the number of large trees. This is caused by the harvest of mangrove wood to produce charcoal for fuel purposes. This condition will slowly make the function of the ecosystem decrease. Where the role of ecosystems provide living niches for aquatic organisms is decreasing. Land clearing of certain areas of the mangrove area for physical infrastructure purposes such as the construction of restaurants, settlements, roads, small aircraft runways, reduces the ability of the region to maintain the function of its ecosystem. The next thing is the ecological pressure for aquatic biota that has living niches in mangrove areas.Keyword: alpheid shrimp, alpheus, mangrove, ecosystem, kuala langsa, aceh

An annotated and illustrated checklist of the porcelain crabs of Panama (Decapoda: Anomura).

The present study is the first exhaustive checklist of porcelain crabs (Porcellanidae) distributed on the Pacific and Atlantic (Caribbean) coasts of Panama, based on literature records and material collected between 2006 and 2019. The Panamanian porcellanid fauna is currently composed of a total of 76 species, with 26 species reported from the Caribbean coast, 45 species reported from the Pacific coast, and five species reported from both sides of the Central American Isthmus (Isthmus of Panama). In other words, the Caribbean and Pacific coasts of Panama each harbour, respectively, 31 and 50 species of porcellanid crabs. However, this total includes two problematic porcellanid records from Panama, viz. Clastotoechus nodosus (Streets, 1872) and Petrolisthes brachycarpus Sivertsen, 1933, as well as a putatively undecribed taxon reported as Pachycheles sp. The following four species are recorded for the first time from Panama, viz. Euceramus panatelus Glassell, 1938, Pachycheles riisei (Stimpson, 1859) [also being new for Mexico], Petrolisthes dissimulatus Gore, 1983 and P. tonsorius Haig, 1960. In addition, Minyocerus kirki Glassell, 1938 is newly recorded from Colombia, extending its previously known distributional range significantly southwards. Most species are illustrated in colour, several for the first time, based on material from Panama or other localities. At least 20 further species (16 in the Atlantic, 5 in the Pacific, and 1 in both oceans) are suspected to occur in Panamanian waters, based on their records from the neighbouring Costa Rica and/or Colombia, or their wide distribution in the Caribbean Sea or the tropical eastern Pacific. The presence of several cryptic or pseudocryptic species (at least some of them presumably undescribed), especially in the taxonomically challenging Petrolisthes galathinus (Bosc, 1802) species complex, or the eventual species splitting within some taxa currently seen as transisthmian, will likely further increase the total number of species present in Panama. The porcellanid fauna of Panama is also ecologically remarkably diversified. Most Panamanian porcelain crabs are free-living under rocks, in crevices of rocks, dead coral heads, coralline algae, coral rubble etc., or on mud, among mangrove roots. Euceramus panatelus lives in possibly self-dug burrows in soft mud or muddy sand, whereas its congener E. transversilineatus (Lockington, 1878) may occasionally be found in association with holothuroids. At least 15 further porcellanid species occurring in Panama live in permanent or facultative associations with a variety of other marine organisms, including sponges, cnidarians (octocorals), echinoderms (sea urchins, sea stars, sea cucumbers), polychaetes (parchment worms) and other decapod crustaceans (hermit crabs), making them one of the most attractive groups for studies of symbiosis-related behaviour and evolution.

Near-field changes in the seabed and associated macrobenthic communities due to marine aggregate extraction on tidal sandbanks: A spatially explicit bio-physical approach considering geological context and extraction regimes

Based on data from Multibeam Echosounders (MBES) and Van Veen grab samples, near-field effects of marine aggregate extraction by trailing suction hopper dredgers in the Belgian part of the North Sea were assessed on a decadal scale. The combined approach allowed to investigate and compare seabed and macrobenthic community characteristics for three extraction areas with similar ecological settings, but with a different geological context and each subjected to a different extraction regime. MBES measurements detected slight alterations of the seabed for areas exposed to a continuous, low extraction regime (monthly average volume = 17 to 83 × 103 m3). However, no significant changes in sediment composition nor the macrobenthic community could be attributed to this low extraction regime. High and continuous extraction in the most intensely extracted area (monthly average volume = 164 × 10³ m³) increased surface heterogeneity and created a local depression, hereby exposing clay and gravel from the underlying geological layer. In this area, the highest environmental impact was observed, as the physical changes in the seabed triggered a shift towards a more heterogeneous, transitional macrobenthic community including opportunistic species and species typically associated with muddy sands. Together with the species already present, this resulted in a local increase in macrobenthos density, species richness and biomass. A high but periodic extraction without screening activity on the most offshore located extraction area (monthly average volume = 230 × 10³ m³, averaged for those months where extraction took place) led to a redistribution of the medium to fine sand fraction and a winnowing of coarse sediment and shell fragments. The decreased median grain size induced a shift in the macrobenthic community from a typical medium to coarse sand Hesionura elongata community towards medium to fine sand representatives of the Nephtys cirrosa community, although the overall macrobenthic density and biomass in this extraction area remained stable. Based on these results, we conclude that extraction regime and local geological context are important factors driving the near-field environmental impact of marine aggregate extraction on tidal sandbanks.

Sedimentology of a coastal shelf sector characterised by multiple bedload boundaries: Plettenberg Bay, inner Agulhas Bank, South Africa

The study deals with a large sand body (spit-bar) attached to the eastern tip of the Robberg Peninsula, Plettenberg Bay, South Africa. To date, the bar has prograded about 8 km beyond the tip of the peninsula. The bar top is predominantly composed of medium sand, the upper slope of fine sand, and the lower slope of fine muddy sand. Stratigraphically, the sedimentology thus documents an upward coarsening, calcareous quartz-arenitic depositional sequence. The spit-bar as a whole forms the eastern end of a sediment compartment that is clearly distinguishable from neighbouring compartments on the basis of its geomorphology, the textural characteristics of the sediment, and the distribution of sediment thicknesses. Aeolian overpass across the peninsula appears to have formed a fan-like sand deposit in its rear, which is perched upon the upper shoreface of the bay as suggested by the bathymetry to the north of the peninsula. It forms an integral part of the sediment body defining the spit-bar. The estimated volume of sand stored in the spit-bar amounts to 5.815 km3, of which 0.22 km3 is contributed by the aeolian overpass sand. The sediment sources of the spit-bar are located up to 100 km to the west, where a number of small rivers supply limited amounts of sediment to the sea and numerous coastal aeolianite ridges in the Wilderness embayment have been subject to erosion after becoming drowned in the course of the postglacial sea-level rise since about 12 ky BP. By contrast, the sediment volume in the adjacent compartment B to the north (Plettenberg Bay), which has been supplied by local rivers, amounts to only 0.127 km3. In a geological context, large sand bodies such as the Robberg spit-bar are excellent exploration models for hydrocarbons (oil and gas).

Habitat utilization and secondary production of the sharp-nosed sand goby Favonigobius gymnauchen around intertidal areas

The sharp-nosed sand goby Favonigobius gymnauchen is one of the most dominant fish species around tidal flats and sandy beaches in Japan and plays an important role in the food web. To clarify the habitat utilization and secondary production of F. gymnauchen in these waters, we investigated the density, size compositions, feeding, and prey availability in sandy beaches, a muddy sand estuary, and a seagrass bed in Hiroshima Bay, central Seto Inland Sea, Japan. The density of F. gymnauchen was the highest in the estuarine habitat and the lowest in the sandy beaches. They mainly consumed copepods, gammarids, and polychaetes. The body sizes of F. gymnauchen were larger in the estuarine habitat than in the seagrass bed, although prey availability was higher in the seagrass bed than in the estuary. Secondary production of F. gymnauchen was the highest (> 1 g wet weight m−2 year−1) in the estuarine habitat. The growth rate in the estuarine habitat was estimated to be 0.2 mm d−1. In a laboratory experiment in which fish were exposed to various salinity conditions and fed excess food, the feeding and growth of F. gymnauchen were not significantly different at salinities of 5, 15, and 30, and the maximum growth of juveniles at nearly 25 °C was estimated to be 0.2 mm d−1. These results indicate that F. gymnauchen grows at nearly maximum rates in estuarine habitats despite their high density, thereby resulting in the high secondary production of this species.

Substratum preferences of juvenile Red belly Tilapia (Coptodon zilli, Gervais, 1848)

Substratum preferences of the young of Alien fish species known as Red belly Tilapia locally known Bultee (Coptodon zilli, Gervais, 1848) [1] with 30–40 mm TL were studied in the laboratory. The work tested the hypothesis that fishes vary in habitat preference and that they make use of the differences in substrates’ types within the water body in nature. Substratum preference for juvenile of C.zilli was calculated by the calculations of individuals noticed inside precise habitat kinds.The fish species demonstrated significant changes in their substrate choices. Muddy sand appears to be usually more appropriate settlement ground for juvenile of this fish. Pebble, Gravel, Sand and Mud were less favorable. Plastic floor was unfavorable and the fish would generally settle in the other substrates preference to it. This work proposed that the particle size of the substrate influences settlement preference of the fish.

Spatial distribution of sea cucumber and their management effort in seagrass ecosystems in Buntal Island, Western Seram Regency

Sea cucumbers belong in the Echinoderms and some of them have a high economic value. The demand for sea cucumber as an export commodity encourages multispecies hunting with various sizes. The objective of this research was to determine the ecological parameters and spatial distribution of sea cucumber. Sampling was conducted in Buntal Island waters from March to June 2017, using the belt transect method. The results showed that there were 12 species of sea cucumbers, of which the Holothuria atra has the highest potential value, density, and frequency of presence compared to Opheodesoma grisea from the 4 stations area. The species diversity index (H’) is in the medium category, the compatibility index (E) is in the stable community, the species dominance value (D) is low. The Morisita index value shows a uniform, random, and group distribution. The sea cucumber is found to distribute in almost all substrates i.e. sand, muddy sand, and sandy mud associated with seagrass. Three management strategies were proposed namely conservation and protection efforts, restrictions on the number and size of sea cucumber caught in a certain period, and improve the understanding and community knowledge of sustainability of the marine natural resources.

Inversion of the sediment sound velocity in the Northern South China Sea

Acoustic models are effective methods for inverting the geo-acoustic properties of seafloor sediments. To investigate the main sediment types in the northern South China Sea, 221 sediment core samples containing three sediment types (clayey silt, silty clay, muddy sand) were collected, and the geo-acoustic properties of the sediments were measured and analyzed. The results show that the same sediment type, shows different acoustic properties for different sedimentary environments. To verify the applications of different acoustic models, three acoustic models (the BS, EDFM and VGS model) were used to invert the sound velocities. It was observed that when porosity is less than about 0.75, the predicted velocity values from the three models are close to the measured values. As the porosity increases, the variation trend of VGS model is more in line with the measured data, while the BS and EDFM model has a relatively large error with the measured data.It seems that the VGS model, which incorporates the properties of both fluids and elastic solids, has a relatively broader scope of application. while the BS and EDFM models are susceptible to the porosity and particle size of the sediment.

Characteristics of Underwater Topography, Geomorphology and Sediment Source in Qinzhou Bay

Human activities for exploitation and utilization of coastal zones have transformed coastline morphology and severely changed regional flow fields, underwater topography, and sediment distribution in the sea. In this study, single-beam bathymetry coupled with sediment sampling and analysis was carried out to ascertain submarine topography, geomorphology and sediment distribution patterns, and explore sediment provenance in Qinzhou Bay, China. The results show the following: (1) the underwater topography in Qinzhou Bay is complex and variable, with water depths in the range of 0–20 m. It can be divided into four underwater topographic zones (the central (outer Qinzhou Bay), eastern (Sanniang Bay), western (east of Fangcheng Port), and southern (outside of the bay) parts); (2) based on geomorphological features, the study area comprises four major submarine geomorphological units (i.e., tide-dominated delta, tidal sand ridge group, tidal scour troughs, and underwater slope) and two intertidal geomorphological units (i.e., tidal flat and abrasion platforms); (3) sandy sediments are widely present in Qinzhou Bay, accounting for 70% of the total sediments. From the mouth of the Maowei Sea to the central and northern part of Qinzhou Bay, the sediments gradually become coarser, shifting from sandy mud to muddy sand, and then to fine sand and medium–coarse sand, especially inside the trench. The detrital minerals contained in the sediments mainly consist of quartz, feldspar, ilmenite, leucosphenite, tourmaline, and detrital minerals, whereas the clay minerals are dominated by kaolinite, followed by illite and smectite. The sediment provenance is mainly terrigenous input from near-source river. With sea reclamation and dam construction, outer Qinzhou Bay has experienced enormous morphological variation of its coastline. Human activities for exploitation and utilization of coastal zones have transformed coastline morphology and severely changed regional flow fields, underwater topography, and sediment distribution in the sea. Together with the channel effect where the velocity of ebb tide is greater than that of flood tide, the underwater topography is characterized by increased scale and height difference of troughs and ridges as well as enhanced offshore deposition.

Meristics and morphometrikcs characters of Scylla serrata in Youtefa and Kalimaro, Papua mangrove ecosystem

Observations of the meristic and morphometric characteristics of S.serrata will be carried out in Youtefa Bay, Jayapura, and Kalimaro, Merauke. The research objective was to determine the morphometric and meristic characteristics and their relationship with the mangrove ecosystem. Homogeneity test results showed homogenous results with a correlation (r) 0.80 and (r) 0.85. The results obtained were 96.05% which was not significantly different in meristic and morphometric characteristics. The substrate fraction of Kalimaro is dominated by clay (26.53%) and fine sand (16.84%) which means that the type of substrate is sandy loam, while Youtefa is dominated by coarse sand (27.00%) clay (15.45%), or muddy sand type. For the C-organic deposits on Youtefa (4.92%) and Kalimaro (9.58%) substrates in the good category, but the correlation results showed Kalimaro (r) 95% while Youtefa (r) -95% with a confidence interval (p> 0.05) is directly proportional to the abundance of Kalimaro (39 individuals/m2) and Youtefa (11 individuals/m2). Mangrove density in Youtefa (4,800-7,800 individuals/ha) is dominated by Rhizophora 73.1% and Kalimaro (2,600-3,700 individuals/ha) is dominated by Avicennia 75%. Mangrove ecosystem has a close relationship on meristic and morphometric characteristics compared to Youtefa Bay.

Recurrence of intraplate earthquakes inferred from tsunami deposits during the past 7300 years in Beppu Bay, southwest Japan

We studied onshore sediment cores obtained from a coastal marsh on the south coast of Beppu Bay, northern Kyushu Island, Japan, to ascertain whether prehistoric intraplate earthquakes in the bay had generated tsunamis, and to establish a chronology and recurrence intervals for these earthquakes. The latter had been inferred from investigations on shallow offshore faults, but the timing of the fault movements has large uncertainties. We identified five sand layers in the up to 8.8 m long sedimentary sequence, which is mainly composed of non-marine organic-rich mud and marine organic-poor mud. Most sand layers, 1–20 cm thick, exhibit sharp upper and lower contacts with the surrounding muds, implying that they were deposited by sudden events. The sand layers are geochemically distinct, with peaks in Si, K, Ca, Ti, Mn, Fe, and Sr, and diatom assemblages dominated by brackish–marine and marine species. This suggests that the sand came from the sea bottom and/or shore rather than from the freshwater marsh. Based on radiocarbon age modeling, the depositional ages of these sand layers are: 3270–3450 cal yr BP, 4250–4510 cal yr BP, 4970–5280 cal yr BP, 5750–6750 cal yr BP, and 6430–7070 cal yr BP. The oldest deposit is inferred to record a tsunami associated with the 7.3 ka caldera-forming eruption of the Kikai volcano, southern Japan. Thus, we exclude it from the calculation of the recurrence interval of tsunamigenic intraplate earthquakes in the bay. Recurrence is approximately 460–1850 years, including the 1596 CE Keicho Bungo earthquake and a fault rupture 1700–2200 years ago, which have been reported in studies on ruptures of shallow offshore strike-slip and normal faults. Brackish–marine and marine species dominate the fossil diatom assemblages in the upper muddy sand layer (younger than 2750–2870 cal yr BP) above the non-marine organic-rich mud, implying that the muddy sand was deposited in an inner bay or tidal flat environment. The facies change from non-marine to marine sediments after 2750–2870 cal yr BP cannot be explained by a change in the regional sea level because the latter has fallen in the last 6000 years. Therefore, the most likely interpretation for this environmental change is a local coseismic subsidence of the marsh, probably attributed to a rupture of the active fault located south of the marsh. This study is the first to report on recurrent tsunamigenic intraplate earthquakes based on research of onshore tsunami deposits, and suggests that investigating tsunami deposits can contribute to an assessment of tsunami risks for intraplate earthquakes elsewhere.

Environmental Factors for Holothuria scabra Sea Cucumber Cultivation

Sea cucumber cultivation is an alternative to anticipate the continuity of production due to overfishing. Maintenance environmental factors are important factors to consider in sea cucumber cultivation. A suitable location really supports the success of sea cucumber cultivation. This study aims to identify the main habitat and indicators in determining a suitable location for cultivation of Holothuria scabra. The study was located in the intertidal zone of the Watuar village seagrass ecosystem during May 2020 to October 2020. The results showed that the location of the Watuar village seagrass beds was suitable to be developed as a sea cucumber cultivation location with three main indicators, namely 35 cm depth (at low tide) and 195 cm (at the highest tide), the condition of the seagrass vegetation is moderate and is the natural habitat of H. scabra with the dominance of the seagrass Enhalus acoroides, Cymodocea rotundata, Cymodocea serrulata, Thalassia hemprecchii with moderate density and the bottom substrate is muddy sand with particle size 100 µm of 96.7%.

Ecobiology of horseshoe crab in Brebes, Northern Coast of Java: Preliminary study

Horseshoe crabs are known as living fossils and three species are found in Indonesia where all of them are being protected. The research aimed to assess ecology, species composition, and biological aspects in Brebes estuary. The research was conducted in August and October 2017 in Brebes Estuary. Samples were caught using local fishermen and experimental gears. Parameters of water quality were observed insitu and substrate was analyzed in the laboratory. The horseshoe crabs were measured morphologically, their stomach and eggs were taken to be analyzed in the laboratory. Total specimens of horseshoe crabs were 33 individuals (Tachypleusgigas=8; Carsinoscorpius rotundicauda=25). T. gigas has 16.3-22.6 cm of prosomal width and 216.1-717.0 gram of weight. C. rotundicauda has 11.2-14.5 cm of prosomal width and 96.0-275.5 gram of weight. Stations with a muddy sand substrate (silt >50%) have the highest number of captured horseshoe crabs. Food habits of T. gigas are macrophytes and detritus while C. rotundicauda are macrophytes, molluscs, annelids, and coral. Niche breadth of C. rotundicauda were wider than T. gigas. High niche overlap value between T. gigas and C. rotundicauda indicates high competition in utilizing food sources. The fecundity of C. rotundicauda was higher than T. gigas but the egg diameter of C. rotundicauda smaller than T. gigas.