Wakasa Bay Research Articles

Secular change in seaweed species composition and coverage of Sargassaceae on the artificial reef in Wakasa Bay, Japan.

The threat of declining seaweed beds has been a concern around the world. Seagrass and seaweed (brown algae) beds are essential habitats supporting fisheries. However, approximately 22% of these habitats have been lost in Japan due to increased coastal landfill sites and ports. This study aims to rehabilitate the depletion of these habitats by constructing an artificial reef in Wakasa Bay, Japan, and monitoring Sargassaceae succession in the second and fourth years after the construction was completed. In this study, we set up four sites on the artificial reef. Then we identified the seaweed species composition and coverage of the Sargassaceae using underwater visual observation by scuba divers. The seaweed coverage was already over approximately 80% in the second year after construction. The Sargassum horneri and S. confusum dominated during the first and second sampling in the second year after construction, and Myagropsis myagroides and S. patens during the third and fourth sampling in the fourth year after construction. Thus, the recovery of species composition takes longer than that of coverage. Therefore, observing species composition recovery is essential when constructing the artificial reef.

Deep subduction of the Philippine Sea slab and formation of slab window beneath central Japan

The geometry of the Philippine Sea slab (PHS) subducting beneath the Japanese islands has been imaged to 400 km depth beneath the Kyushu and Chugoku regions, whereas the PHS slab geometry beneath the Hokuriku region has only been determined to ~ 140 km depth, thereby indicating a large east–west asymmetry in the slab subduction. However, geologic evidence suggests that there was symmetrical east–west seafloor spreading along the axis of the Kinan seamount chain when the Shikoku basin was an active spreading center in the PHS plate. This inconsistency suggests that the PHS slab should be present beneath the Hokuriku region. Here we perform P-wave travel-time tomography across central Japan and conduct a two-dimensional plate subduction numerical simulation that reproduces the dual subduction of the PHS and Pacific (PAC) plates to elucidate the PHS slab geometry beneath central Japan. The tomography results reveal a high-velocity anomaly at ~ 150–250 km depth that extends from Wakasa bay to Noto peninsula and a slab window beneath the Hokuriku region. The numerical simulation results suggest that the PHS slab may have torn when it collided with the PAC slab, with the once leading edge of the PHS slab now present along the upper surface of the PAC slab beneath Noto peninsula. These results indicate that the PHS slab exists at ~ 250 km depth beneath the Hokuriku region, although it has been torn owing to its collision with the PAC slab, with this tear propagating westward to form a triangular slab window beneath the Hokuriku region.Graphical

A new species of the alpheid shrimp genus Athanas Leach, 1814 (Decapoda: Caridea) from the Sea of Japan.

A new species of the alpheid shrimp genus Athanas Leach, 1814 is described based on a holotype from Wakasa Bay, Sea of Japan side of Honshu, Japan, at a depth of 90 m. Athanas exilis n. sp. appears close to A. sydnyensis Anker & Ahyong, 2007, but is distinguished from the latter by some morphological features, including the different shape of the telson, the shorter antennular stylocerite, more strongly produced distal lamella of the antennal scaphocerite, and less developed armature of the merus of the major cheliped. Preliminary genetic analysis using the mitochondrial 16S rRNA gene was performed to compare interspecific genetic divergence within the genus.

A numerical study of lightning-induced NOx and formation of NOy observed at the summit of Mt. Fuji using an explicit bulk lightning and photochemistry model

This study coupled a meteorological model with explicit bulk lightning and chemical transport models to investigate the impacts of lightning-induced nitrogen oxides (LNOx) on nitrogen monoxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen oxide (NOy) measured on August 22, 2017, at the top of Mt. Fuji, Japan. Our simulation results indicated that the LNOx emitted around Wakasa Bay in the windward area of Mt. Fuji largely contributed to the NOy content measured at the top of Mt. Fuji. Furthermore, sensitivity experiments regarding the height of LNOx emissions indicated that the NOy content measured atop Mt. Fuji originated from LNOx emitted below 6 km. Our simulation assumed that a two-mode vertical distribution of LNOx emissions was more consistent with measured NOy at Mt. Fuji than a single-mode structure assumption in this case. A comparison of simulated NOx (= NO + NO2) and measured NOx at Mt. Fuji indicated that the reaction rates of the NO and NO2 cycles were well reproduced in our model; however, the ratio of NOz (NOy species other than NOx) to NOy estimated by the model were lower than the observed value, implying that the model either underestimated the reaction rate of LNOx or overestimated the wet removal of lightning-induced NOz. Finally, our results also suggest that the simultaneous observation of NOy and NOx is important for understanding LNOx emissions, subsequent atmospheric chemical reactions, and removal processes, as well as validating chemical transport models.

Genetic analysis distinguished new natural population and old plantations of Cryptomeria japonica

Natural forest is important not only for conserving genetic diversity, but also as a future breeding resource, especially for forestry tree species. Cryptomeria japonica is an important forestry tree species in Japan, but natural populations are limited. We discovered apparently natural C. japonica individuals on Mt Aoba, adjacent to Wakasa Bay in Fukui Prefecture, Japan. The area around Wakasa Bay was an important refugia for this species during the Last Glacial Maximum. To clarify whether these individuals are natural origin or not, we sampled 195 individuals with a diameter at breast height (dbh) greater than 60 cm (with an average dbh of 79 cm), and conducted genetic analyses with 249 SNP and 20 SSR markers. We found two genetic clusters identified as ura-sugi and omote-sugi lineages and the genetic diversity of the sample was similar to known natural populations. The ura-sugi lineage showed a clear correlation between age and dbh, whereas the omote-sugi lineage showed no correlation. The ura-sugi lineage was also genetically very similar to nearby natural populations. Most of the omote-sugi lineage trees were about 100 years old regardless of dbh, and located in one small valley close to a village. The results suggest that the ura-sugi lineage (124 individuals) represents a population of natural origin, whereas the omote-sugi lineage (60 individuals) population was probably planted about 100 years ago using trees of non-local origin. Seven individuals appeared to be hybrids, displaying both ura-sugi and omote-sugi lineages. In situ conservation of the ura-sugi individuals should be a priority, after removing the omote-sugi lineage, in order to conserve the natural genetic resources they represent. Ex-situ conservation strategies should also be implemented to protect the endemic gene pool from gene flow from the many C. japonica plantations in the surrounding area.

Seasonal variation in the community distribution of protists off Wakasa Bay, Southern Sea of Japan

There is a dearth of knowledge regarding the spatiotemporal distribution of protistan community composition and seasonal environmental changes. High-throughput sequencing of the 18S rRNA gene was performed to assess changes in the community composition of protists over four seasons at four sites in Wakasa Bay, located in the center of Japan's northern coast. The community composition varied seasonally rather than geographically, even among few local communities confined to the bay head. Throughout the year, Alveolata and Chlorophyta were widely distributed and represented the predominant groups. Groups I and II of Syndiniales and Dinoflagellata were significant taxa in terms of operational taxonomic unit richness and sequence read abundance. Although three lineages of prasinophyte Clade VII, Pycnococcus-related prasinophyte, and Ostreococcus-related Mamiellophyceae were common, prasinophyte Clade VII was dominant during summer–autumn, whereas others were dominant during winter and spring. These results indicate the differential dominance of Chlorophyta at the intrataxon level. In the protistan community, increased temperature exerted an effect on the summer–autumn composition, whereas increased nitrate concentration showed an effect on the winter composition, suggesting that seasonal environmental changes affect the protistan community composition with different fluctuation patterns being observed among taxa.

1. The prevention of infectious diseases on sea-cultured rainbow trout in Wakasa Bay

1. The prevention of infectious diseases on sea-cultured rainbow trout in Wakasa Bay

A new species of the ghost shrimp genus Callianassa Leach, 1814 (Decapoda: Axiidea: Callianassidae) from Wakasa Bay, western Japan: the first representative of the genus from the Pacific region.

The ghost shrimp genus Callianassa Leach, 1814 is currently represented by six taxa, of which five are known from the eastern Atlantic and only C. persica Sakai, 2005 from the Persian Gulf. In this study, a new species of Callianassa is described and illustrated on the basis of material from the subtidal soft sediments (at 2628 m depth) in Wakasa Bay, western Japanese coast of the Sea of Japan. Callianassa ogurai n. sp. is the first species of the genus from the Pacific region. This study discusses characters differentiating the new species and other five congeneric species. Molecular phylogenetic analysis using the mitochondrial 16S rRNA gene supports the close relationship between the new species and C. subterranea (Montagu, 1808), warranting the generic assignment of the new species to Callianassa sensu stricto. We also explore the contentious taxonomic status of C. timiris (Sakai, Trkay, Beck Freiwald, 2015).

Groundwater-surface water exchange affects nitrogen and phosphorus exports from tideless rivers to a ria coast in the sea of Japan

• Groundwater discharge in the downstream area of six tideless rivers was quantified. • Riverbed slope affected the relative contribution of groundwater to surface water. • Groundwater-derived nitrogen and phosphorus were critical for the coastal ecosystem. Groundwater discharge in downstream regions along the river continuum is considered a significant source of water and nutrients. However, the influence of groundwater discharge on the net export flux of surface water and nutrients from tideless rivers to coastal seas has not been thoroughly assessed. We conducted field surveys in the downstream region of six tideless rivers with different watershed properties along the ria coast of Wakasa Bay in the Sea of Japan during the summer. Mass balance models of water, salt, and 222 Rn were constructed to determine groundwater fluxes and associated fluxes of nitrogen and phosphorus. The model revealed that groundwater discharge ranged from 0.08 to 3.89 m d −1 , accounting for 1.3–14.8% of the export flux. This variability among the rivers correlated with the riverbed slope in each river, indicating that the local topographic gradient was a significant factor controlling groundwater-surface water exchange in tideless rivers. Groundwater discharge accounted for 0.8–16.7% of the nitrogen export and 0.9–27.4% of the phosphorus export to coastal seas. We concluded that the groundwater inflow driven by the hydrological and geographic properties of the watershed in the downstream region of tideless rivers was nonnegligible for nutrient dynamics and biological production in the coastal seas.

Preface: Functional biogeography in Japanese cedar

Preface: Functional biogeography in Japanese cedar

The Quest for an Ideal Culinary Hyperlocalism

The Quest for an Ideal Culinary Hyperlocalism

若狭湾沖海底堆積物コアに挟まる後期更新世から完新世テフラの層序と広域テフラとの対比

若狭湾沖海底堆積物コアに挟まる後期更新世から完新世テフラの層序と広域テフラとの対比

『諸国御客船帳』にみる近世の海運業 －讃岐国粟島と若狭国早瀬をめぐる海上文化史－

『諸国御客船帳』にみる近世の海運業 －讃岐国粟島と若狭国早瀬をめぐる海上文化史－

Genetic Diversity and Population Genetic Structure of Korean Black Scraper Thamnaconus modestus in Korea and Japan Based on the mtDNA Marker

Thamnaconus modestus is a commercially important species that is widely distributed in the Northwest Pacific region. To investigate the genetic diversity, demographic history, and population structure, 84 individuals were collected from two locations in Korea (Geomundo and Jumunjin) and one location in Japan (Wakasa Bay). Analysis of the mitochondrial DNA control region sequence of 373 base pairs from the 84 individuals revealed 39 haplotypes with 50 polymorphic sites. The haplotype diversity and nucleotide diversity of different populations ranged from 0.973 (0.018) to 0.981 (0.013) and from 0.020 (0.011) to 0.021 (0.011), respectively. Phylogenetic analysis revealed three distinct clades of which two were large (clade 1 and clade 2) and one was small clade (clade 3). However, there was no significant geographical clustering of the haplotypes according to the sampling locality. Demographic analysis suggested that both clades experienced Late Pleistocene population expansion. The pairwise FST and AMOVA analysis were insignificant among the populations investigated. This indicated high gene flow among the populations of Korea and Japan. The dispersal capacity of the larvae and juveniles by ocean currents and migration of adult individuals could explain the genetic homogeneity. Insufficient time to accumulate genetic variation might be another reason for the lack of genetic structure.

Long-term trends of oxygen concentration in the waters in bank and shelves of the Southern Japan Sea

While multiple studies have investigated oxygen decrease in Japan Sea Proper Water (JSPW; > 300 m in depth), oxygen variation in continental slope and shelf waters (< 300 m) must also be investigated in order to assess its socioecological impacts. In this study, historical oxygen data in the waters of three continental shelves and a bank of Japan Sea, off-Awashima area (AW), Wakasa Bay (WB), East of Tsushima Straight (ETS), and Yamato Bank (YB), were collected and analyzed to assess temporal variation of oxygen in each region from 1960 to 2000s. Significant decreasing trends of oxygen were detected in the waters below 150 m depth in WB and YB, and below 300 m in AW, in the summer season. In winter, a decreasing trend of oxygen was detected throughout the water column from 300 m to the sea surface in WB and YB. In ETS, a deoxygenation trend was detected throughout the water column from the bottom to the sea surface in the summer season, while no trend was detected in winter. The results suggested that oxygen decreases in AW, WB, and YB were the consequence of the upward propagation of the deoxygenation signal from JSPW, while that of ETS was caused by horizontal propagation of deoxygenation signal from the East China Sea. Assuming that the observed trend will continue in future, it is predicted that part of the water in Tsushima Strait area will reach the general sublethal threshold of oxygen (134 μmol kg−1) by the end of this century.

First records of Callogobius tanegashimae in Wakasa Bay, the Sea of Japan coast of central Japan

First records of <i>Callogobius tanegashimae</i> in Wakasa Bay, the Sea of Japan coast of central Japan

Kyucho in Wakasa Bay induced by Yura river flushing

Kyucho in Wakasa Bay induced by Yura river flushing

Genetic diversity and population structure of Pacific herring Clupea pallasii in the Northeast Asia inferred from mtDNA marker

Pacific herring ( Clupea pallasii ) is an important commercial species in the Northeast Asia including China, Korea, Japan, and Russia. To investigate the genetic diversity and genetic differentiation among populations based on mtDNA control region sequence, 122 individuals were collected from the three locations of Korea (Imwon, Pohang, Jinhae) and one location from Japan (Wakasa bay). In addition, 39 and 48 individuals sequence from China (Rongcheng) and Russia (Krasnogorsk) respectively, were downloaded from the Genbank. Analysis of nucleotide sequence of 419 bps revealed the haplotype diversity ranged from 0.9080 to 0.9646 and nucleotide diversity ranged from 0.0098 to 0.0133. Pairwise F ST comparisons evident no significant differentiation among the sampling localities from China, Korea, and Japan. However, Russia population showed significant differentiation from all the Korean populations. Both the neutrality test and mismatch distribution showed that C. pallasii populations experienced a demographic history of population expansion. The starlike minimum spanning tree and haplotype and nucleotide diversity also indicate demographic history of population expansion. • Clupea pallasii showed genetic homogeneity in Korea, Japan and China. • Comparatively low genetic diversity in China population than Korea and Japan. • Historical climatic changes and contemporary factors influence the genetic patterns. • Findings will play an important role in conservation.

若狭の海でIoTを活用した鯖養殖の挑戦 ～「鯖，復活」プロジェクト～

若狭の海でIoTを活用した鯖養殖の挑戦 ～「鯖，復活」プロジェクト～

オオクチイケカツオScomberoides commersonnianus （アジ科）の山口県日本海沿岸からの記録および 若狭湾とその周辺海域に出現するアジ科魚類目録

オオクチイケカツオScomberoides commersonnianus （アジ科）の山口県日本海沿岸からの記録および 若狭湾とその周辺海域に出現するアジ科魚類目録