Beaches In Japan Research Articles

Distribution of microplastics on sandy beaches in western and southern Japan and their fate in the oceans

The Japanese archipelago is surrounded by the Sea of Japan, the Sea of Okhotsk, the Pacific Ocean, and the East China Sea. The oceans are known to be contaminated by waste artifacts (marine litter). To investigate how these artifacts contaminate sandy beaches in Japan and their fate in the oceans, we sampled sand from 19 sandy beaches ranging from the western area of the main island of Japan (Honshu), which faces the Sea of Japan, to the westernmost island in the Japanese archipelago (Yonaguni Island), which faces the East China Sea. Almost all beaches were contaminated by marine litter. The maximum density by number of pieces was 604,600 per m3 in a 2-cm depth of sand on Yonaguni Island. Polystyrene foam was the most common artifact, and plastic fragments were second. The densities of artifacts by number and weight, and the type of artifacts, varied by location. A statistically significant positive relationship between the weights of artifacts and natural objects was observed, suggesting that they experience similar fates in the oceans. The major axis of the polystyrene foam in the Yonaguni area differed significantly from those in the Shimane, Tsushima, and Okinawa areas. The major axis in the Tsushima area significantly differed from those in all other studied areas. This study found the geological difference in the distribution and the major axis of polystyrene foams. These differences may be relevant to environmental physical factors (wind, rain, and waves), chemical alterations by ultraviolet rays, exposed time, the gyre, and local currents.

Artificial neural network based model to predict mega cusp characteristics in Hasaki, Japan

Cusps, characterized by a series of horns and embayments, are notable coastal features observed along shorelines in various areas. When the horn-to-horn distances of cusps are substantial, they are referred to as mega cusps. There is a scarcity of measured morphological data for mega cusps, especially long-term data, making it challenging to acquire comprehensive insights. In this study, the morphodynamic characteristics of mega cusps such as mega cusp cross-shore extent and length were analyzed using data collected from Hasaki Beach in Japan over the period of 2007 to 2020. The analysis aimed to address the lack of accurate formulation and numerical models for simulating mega cusp morphological characteristics, which poses another obstacle in mega cusp prediction. To overcome this, different Artificial Neural Networks (ANNs) were employed to predict the horn-to-horn and horn-to-embayment distances of mega cusps following storm events. Storm wave parameters, including significant wave height, wave period, and wave direction, along with additional data such as cumulative energy flux and storm event duration, were utilized as input variables for the ANNs. The accuracy of the predicted results was assessed using the Pearson correlation coefficient, which was calculated based on a comparison with field data. The findings of this study demonstrated that the inclusion of significant wave height, wave period, wave direction, cumulative energy flux, and storm duration in the ANNs yielded satisfactory accuracy in predicting mega cusp characteristics. Overall, this investigation contributes to advancing our understanding of beach mega cusp dynamics and offers a viable approach for predicting mega cusp characteristics by utilizing artificial neural networks and incorporating relevant storm wave parameters.

Nagisavelia hikarui, a new genus and species of Mesoveliinae (Hemiptera: Heteroptera: Mesoveliidae) inhabiting shingle beaches in Japan.

A new genus and species of Mesoveliinae, Nagisavelia hikarui n.gen. and n.sp., is described from rocky intertidal beaches in Japan. The new taxon is compared to the other 10 genera of Mesoveliinae, and a character matrix for the identification of eight genera is provided. A key to facilitate the identification of the seven species of Mesoveliidae now reported from Japan is also provided.

STUDY OF DETERMINING RISK LEVEL REGARDING SWIMMING CONDITION ON BATHING BEACH USING AI

In Japan, 2,000 to 3,000 drowning accidents occur every summer season at major bathing beaches. In order to prevent drowning accidents, beachgoers themselves need to be aware of the dangers and avoid them. As a way to do this, bathing beaches provide daily risk levels regarding swimming conditions to beachgoers using three levels of beach safety flags. However, the risk levels are determined subjectively and empirically by lifesavers and beach administrators based on weather and sea conditions. The characteristics of past drowning accidents are not taken into account. In this study, we suggest an objective method of determining the risk levels based on the probability of drowning accidents. We have created an AI model that can predict the probability of drowning accidents with high accuracy using a total of 53 features such as usage, weather and sea conditions of a study beach in Japan. This method enables appropriate judgment of swimming conditions to prevent many drowning accidents. The reliability of the model was examined using XAI, and it was found that time series of rescue factors were important in predictions. On the other hand, the accuracy decreased when the created AI model was applied to other beaches. It was thought to be caused by differences in the natural environment such as waves and wind.

STUDY OF METHODS FOR DETECTING OCCURANCE OF RIP CURRENT USING IMAGE ANALYSIS

There are from 2,000 to 3,000 rescues every summer at bathing beaches in Japan, and the main cause of drowning accidents is rip currents. To analyze the rip current, a method for visualizing rip currents with average images can be used. However, in case of the investigation over a long period, such as several months, it is necessary to confirm the occurrence of rip currents through thousands of averaged images by human eyes. In this study, we suggested a new method for detecting the occurrence of rip currents automatically by analyzing the pixel values of averaged images. Images for the analysis were created from video data recorded in March and April 2021 by a camera overviewing the study beach located on the west coast of Japan. The accuracy results of this method were 99 percent for the validation dataset and 57 percent for the verification dataset, respectively. When the wave height was 0.5 m and higher for the verification dataset, the accuracy was 75percent. Therefore, it was considered that this method can detect the occurrence of rip currents when the wave height is 0.5 m and higher. As a result of applying this method to the 3-month image data recorded from October to December 2021, it was found that wave steepness was occurring lower under the conditions of rip currents. In conclusion, this method was able to automatically detect the rip currents from the images, and the conditions of waves when the rip currents that occurred could be investigated using this method.

Cross-sectional microstructural analysis to evaluate the crack growth pattern of weathered marine plastics

Fragmentation of degraded plastics and release of smaller secondary microplastics is usually attributed to the growth of environmental stress cracks. Analysis of crack patterns derived from chemical degradation can be useful not only for assessing the cause of plastic fracture and evaluating the useful lifetime of a product, but it can also potentially provide valuable information on the generation of microplastics. However, the literature with respect to microplastics generation is generally limited to surface observations of polypropylene and polyethylene. Here, we used ion-beam milling to prepare cross-sections of fragments of 15 plastic products made from five commodity plastics (polypropylene, polyethylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate) that were collected at two beaches in Japan, and then we examined the microstructures of those cross-sections by means of scanning electron microscopy and energy dispersive X-ray spectroscopy. Crack growth in the depth direction was examined to provide insights into microplastic generation behavior. In all of the polypropylene samples, and some of the low-density polyethylene and polystyrene samples, cracks with a depth exceeding 100 μm from the sample surface were observed. Considering that crack growth causes fracture of degraded plastic and microplastic release, these observations suggest the release of sharp-edged microplastics from the crack fracture surface. In contrast, in the high-density polyethylene and polyvinyl chloride samples, crack growth was limited to within 20 μm of the sample surface, suggesting the release of irregularly shaped microplastics and additive particles. The present results suggest that the degradation behavior of plastic products in the depth direction is dependent on the type of plastic.

Pseudothinusa sunahama, a new genus and species of the tribe Athetini (Coleoptera, Staphylinidae, Aleocharinae) from sandy beaches in Japan

Pseudothinusa sunahama Tasaku & Maruyama gen. et sp. nov. (Aleocharinae) is described based on specimens collected from sandy beaches on the islands of Hokkaidô, Honshû, Shikoku, and Kyûshû, Japan. Pseudothinusa sunahama is the first Japanese athetine species discovered with spines on the front and middle tibiae.

Climate change driven shoreline change at Hasaki Beach Japan: A novel application of the Probabilistic Coastline Recession (PCR) model

Low elevation coastal zones around the world are increasingly threatened by the effects of climate change, and adaptation in these areas is becoming urgent. One of these threats, especially to sandy beaches, is the slow chronic landward movement of the coastline, known as coastal recession. The Probabilistic Coastline Recession (PCR) Model is a physics-based approach that is specifically designed to support modern day risk informed coastal zone management. Here, the PCR model is applied at the highly monitored Hasaki Beach in Japan, which presents challenges that have hitherto not been experienced in previous applications of the model elsewhere in the world (e.g. lack of a clear correlation between high wave events and beach erosion, no storm erosion of dunes but only of the beach strong seasonal variation in erosion events). Therefore, the model is here applied following a novel approach to derive projections of coastal recession (here indicated by shoreline retreat) at Hasaki, under the two end-member IPCC scenarios (RCP 2.6, RCP 8.5.)Shoreline retreat is computed in two different ways that may be useful for two different management purposes; method (a) for computing the probability of erosion reaching and damaging an infrastructure or settlement at any time, and method (b) for computing the average shoreline retreat by a certain future time horizon. Projections for the end of the 21st century obtained with PCR method (a) indicate median shoreline retreats of 17 m (RCP 2.6) and 29 m (RCP 8.5), while those obtained with PCR method (b) are −15 m (RCP 2.6) and −7 m (RCP 8.5) (positive values indicate retreat and negative values indicate progradation). Bruun rule projections, which are comparable with those obtained from PCR method (b), indicate end-century shoreline retreats of 36 m and 66 m at Hasaki, for RCP 2.6 and RCP8.5 respectively. These projections fall at around 34% and 21% exceedance probability PCR method (b) projections respectively, consistent with several previous studies which also show that Bruun rule provides larger coastal recession projections compared to the PCR model. Furthermore, the Bruun Rule appears to provide increasingly conservative (relative to the PCR model) recession projections with increasing time horizons.

Evaluating XBeach performance for extreme offshore-directed sediment transport events on a dissipative beach

ABSTRACT The performance of the process-based nearshore model XBeach for predicting extreme offshore-directed sediment transport was investigated using field observations at a dissipative beach in Japan. Three extreme erosion events were identified from a record of 6,209 observations of the cross-shore profile change at Hasaki, Japan, from 1987 to 2003. The analysis considered the sensitivity of the wave nonlinearity of short waves that could be tuned using the parameter, fua , to the observed bed profile change. The comparisons revealed that for extreme offshore-directed sediment transport events, fua = 0.0 is the best fit for predicting these extreme beach profile changes. In the nearshore zone, erosion was underestimated, and the BSS exhibited low values. Peak sediment deposition occurred in the bar-offshore zone with sediments transported from the nearshore zone and was estimated by the model reasonably well. In addition to the three extreme events, 14 other large events were identified, and the trends of beach profile change could be estimated with sufficient tuning of the fua parameter. After analyzing the correlation between fua and wave and morphology-related parameters, the fua value could be correlated to the observed volume change. This suggested that if there were a rough estimate of the expected total volume change, this may help in setting fua value.

Can the visualization of rip currents prevent drowning accidents? Consideration of the effect of optimism bias

Drowning accidents at beach in Japan are caused by rip currents. To reduce these accidents, a new technology that can detect rip currents and notify beachgoers by using the Internet of Things (IoT) and Artificial Intelligence (AI) was proposed. However, studies on the effect of visualizing rip currents or considering the effect of optimism bias have not been conducted. This study investigates if visualization of rip currents might help in preventing drowning accidents, while considering the effect of optimism bias. The participants were 90 Japanese beachgoers. They were asked to answer questions based on their knowledge of the beach and rip currents, their optimism bias regarding rip currents, and awareness with or without visualization. The results of the analyses suggest that despite optimism bias, the visualization of rip currents increases the tendency of beachgoers to perceive and avoid rip currents. As described above, it was found that by visualizing the rip current, beachgoers were able to perceive and avoid rip currents. In addition, an understanding of rip currents is positively related to the intent to avoid rip currents even when rip currents are visualized. Therefore, it is necessary not only to enhance the avoidance tendency by visualizing rip currents, but also to further enhance knowledge of beachgoers to deepen the understanding of rip currents including the danger associated and methods to avoid them.

Analysis of the contributing factors to infragravity swash based on long-term observations

Predicting the runup heights from the offshore waves and beach characteristics has been one of the most important issues in coastal engineering. Various parameters are considered potential contributing factors, but some of them have not been verified in the field. This study discusses the characteristics of infragravity (IG) swash and its relationship with the offshore wave parameters by analyzing the nine-month field observation data of waves and their runup at a sandy beach in Japan. In particular, the contribution of the frequency spread and directional spread was investigated using field data. IG waves developed as bound waves in a shoaling zone, while they caused frequency-dependent dissipation in the surf and swash zone, which affected the IG swash. The lower frequency components of incoming IG waves generated a larger swash than the higher frequency components when IG wave dissipation was not negligible, but the latter was higher without the dissipation. The integrated IG swash was roughly proportional to H0L0, where H0 is offshore wave height and L0 is offshore wavelength. Furthermore, the inclusion of the frequency spread and directional spread improved the IG swash prediction. An increase in the frequency spread and decrease in the directional spread tended to increase the IG swash, which is in qualitative agreement with the bound wave characteristics. The contribution of the directional spread becomes prominent under energetic conditions. The definition of the offshore wave period also affected the swash prediction, and the spectral mean period gave better performance than the peak period during multimodal wave conditions.

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.

Plant debris are hotbeds for pathogenic bacteria on recreational sandy beaches

On recreational sandy beaches, there are guidelines for the management of bacterial pollution in coastal waters regarding untreated sewage, urban wastewater, and industrial wastewater. However, terrestrial plant debris on coastal beaches can be abundant especially after floods and whilst it has rarely been considered a concern, the bacterial population associated with this type of pollution from the viewpoint of public health has not been adequately assessed. In this study, microbes associated with plant debris drifting onto Kizaki Beach in Japan were monitored for 8 months throughout the rainy season, summer, typhoon season, and winter. Here we show that faecal-indicator bacteria in the plant debris and sand under the debris were significantly higher than the number of faecal bacteria in the sand after a 2015 typhoon. When we focused on specific pathogenic bacteria, Brevundimonas vesicularis and Pseudomonas alcaligenes were commonly detected only in the plant debris and sand under the debris during the survey period. The prompt removal of plant debris would therefore help create safer beaches.

CROSS-SHORE MODEL APPLICATION TO HASAKI BEACH, JAPAN: EVALUATION OF PARAMETER SETTING

Japan's coasts is being suffered by significant erosion. There is already a high demand to protect coasts from the erosion but climate change threatens further erosion. Udo and Takeda (2017) projected future beach loss in Japan due to sea-level rise using Bruun rule. However, its restrictive assumption that they probably do not exist in nature makes difficult to assess uncertainties of the projection results. In this paper, Cross-shore (CS) model developed by Larson et al. (2016), which is more realistic model considering the cross-shore sediment exchange, is applied to calibrate the parameter settings at Hasaki beach in Japan, and model applicability was evaluated.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/sOFr9Jb5a_s

A novel poly(3-hydroxybutyrate)-degrading actinobacterium that was isolated from plastisphere formed on marine plastic debris

Plastic debris surfaces in marine environments provide novel habitats for marine microbes. This type of microbial community is known as a “plastisphere”. Prior metagenomic analyses of plastispheres suggest that the surface of marine plastic debris contain plastic-degrading microbes. Here, we focus on plastisphere as a microbial source. We isolated strain OK12 from plastic bag debris collected from a beach in Japan. The strain grew on a mineral medium supplemented with poly(3-hydroxybutyrate) [P(3HB)] as the sole carbon source. Genetic and biochemical analyses demonstrated that the strain belongs to the genus Nocardioides. In addition, the average nucleotide identity value of the two genomes of the strain OK12 and Nocardioides marinisabuli DSM 18965, a marine species, was 98.3 %, above the 95 % threshold. The strain did not grow above 50 °C, and the optimum temperature for growth was 30 °C. The strain grew and degraded P(3HB) in a broad range of NaCl concentrations (0.01–2.4 M), whereas it did not grow without NaCl, suggesting that the strain is a marine species. The strain degraded the P(3HB) film at a fast rate, despite the fact that the P(3HB) degrading activity in the culture supernatant was low. The strain formed biofilms on the P(3HB) and polypropylene film surfaces. This biofilm formation may have helped the strain to degrade P(3HB).

De novo assembly and characterization of transcriptome in the medicinal plant Euphorbia jolkini

Euphorbia jolkini, a medicinal herb that grows on the warm beaches in Japan and South Korea, is known to be used for traditional medicines to treat a variety of ailments, including bruises, stiffness, indigestion, toothache, and diabetes. It is to analyze the whole transcriptome and identify the genes related to the phenylpropanoid biosynthesis in the medicinally important herb E jolkini. Paired-end Illumina HiSeq™ 2500 sequencing technology was employed for cDNA library construction and Illumina sequencing. Public databases like TAIR (The Arabidopsis Information Resource), Swissprot and KEGG (Kyoto Encyclopedia of Genes and Genomes) were used for annotations of unigenes obtained. The transcriptome of E. jolkini generated 139,215 assembled transcripts with an average length of 868bp and an N50 value of 1460bp that were further clustered using CD-HIT into 93,801 unigenes with an average length of 847bp (N50-1410bp). Sixty-three percent of the coding sequences (CDS) were annotated from the longest open reading frame (ORF). A remarkable percentage of unigenes were annotated against various databases. The differentially expressed gene analysis revealed that the expression of genes related to the terpenoid backbone biosynthesis pathway was higher in the flowers, whereas that of genes related to the phenylpropanoid biosynthesis pathway was both up- and downregulated in flowers and leaves. A search of against the transcription factor domain found 1023 transcription factors (TFs) that were from 54 TF families. Assembled sequences of the E. jolkini transcriptome are made available for the first time in this study E. jolkini and lay a foundation for the investigation of secondary metabolite biosynthesis.

Nia lenicarpa sp. nov. (Niaceae, Agaricales) from Red Sea mangroves in Saudi Arabia with comments on Nia vibrissa

An undescribed Nia species was recorded from intertidal decayed wood of Avicennia marina collected from Red Sea mangroves in Saudi Arabia. Nia lenicarpa sp. nov. is characterized by smooth basidiomes, growing singly or in groups of 2 to 10 confluent basidiomes, with a three-layered, thick peridium and 4-spored basidia. Nia lenicarpa differs from N. vibrissa by having smaller basidiomes without peridial hairs but with thick peridia, larger basidia and basidiospores. Phylogenetic analyses of SSU and LSU rDNA placed N. lenicarpa in a monophyletic clade with two N. vibrissa clades. There are no molecular data available for the other two Nia species; N. epidermoidea and N. globispora. The morphology of N. vibrissa from driftwood collected from a beach in Japan is illustrated. Vertical sections of basidiomes of the Japanese material showed the presence of an outer peridium that is formed by the tips of the peridial hairs which was not reported before. This supports the presence of several cryptic species in the N. vibrissa complex.

Effect of Climate Change on Beaches in Japan

Future beach loss in Japan are reported to be more than 90% due to sea level rise in the worst case. Beaches are affected not only by the sea level rise but also by rainfall and wave characteristic changes and others. This paper reviews past and future beach loss in Japan in a national scale and introduces projection method of future beach loss due to sea level rise and rainfall characteristic change. Even past beach loss and sediment budget are not easy to be quantitatively elucidated in coastal catchments in a national scale, then realistic future beach loss projection is much more challenging. Both further past data analysis and beach profile model improvement/development are necessary for better beach loss projections.

Projection of decrease in Japanese beaches due to climate change using a geographic database

ABSTRACTThis study models shoreline retreat due to sea level rise by using geographic data and applies the model to future projections of decreases in beach area for 806 beaches in Japan. The model uses a foreshore slope (angle) based on data from a digital elevation model, and influence of the present simplified method for estimation of the shoreline retreat is examined through comparisons with previous studies at typical locations. The proposed method gives a distance of shoreline retreat due to sea level rise similar to that predicted using the Bruun rule for minimal retreat less than 30 m, but the difference becomes substantial for more extensive decreases. The decrease in beach area is projected for different sea level rises based on four Representative Concentration Pathway (RCP) scenarios from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. The decrease in beach area becomes more severe for the RCP8.5 scenario, and the proposed method predicts that a third of current sandy beaches in Japan will disappear. The extent of the decrease depends not only on the sea-level-rise scenario but also on the SLR projection model.

Coastal Monitoring Program of Bathymetry Using Video Images Technique

The objective of this research is to investigate the capabilities of optical remote sensing to monitor bathymetry in nearshore area using video images. The technique is designed to extract wave number components based on variation of intensity of brightness at each pixel in the images using cross-spectral correlation approach. This approach is based on pixel array analysis that utilizes a nonlinear inverse method ‘Levenberg-Marquardt’. The technique is applied to the data collected at Hasaki beach in Japan from August to December 2006. The results indicate that the estimate of nearshore bathymetry is proved reasonable accurate near shoreline and breaking area where the differences between estimated and survey water depth are less than 10-30 cm.