Mikawa Bay Research Articles

FIELD MEASUREMENT OF SAND MOVEMENT ON RIVER-MOUTH TIDAL FLAT USING COLOR SAND TRACING

The color sand tracing to investigate the characteristics of sand movement on the tidal flat (Rokujo-gata in Mikawa Bay, Japan) was conducted in the winter season. Field measurements of currents and water level were also conducted on the flat to grasp the driving factors of currents and sand movement. Currents on Rokujo-gata were affected by wind in alongshore direction which is the north-south direction, and by a tidal oscillation in cross-shore direction. In the winter season, the southward currents are dominant. However the strong northward currents are occasionally generated. It is supposed that these strong currents move sand actively on the tidal flat. The color sand was placed on Rokujo-gata. The sand tracing was conducted during 6 months by sand sampling at 18 locations in the tidal flat and color sand grain counting was also conducted. The color sand was scattered soon after the placement. However it was demonstrated that the color sand remained on the tidal flat even after 6 months.

三河湾奥部での高潮発生に伴う知多湾での高水位領域の形成機構

The severe storm surge was occurred at the eastern part (Atsumi Bay) of Mikawa Bay due to Typhoon 0918. The high water level region was simultaneously induced in the western part (Chita Bay) of the bay. The formative mechanism of the region was investigated in this study. The high water level condition around Chita Bay occurred prior to the storm surge in Atsumi Bay by easterly winds of typhoon approaching. Strong currents, which are a part of counter-clockwise circulation in Mikawa Bay, were generated at the mouth of Chita Bay during the surge. It is inferred the currents pushed sea water into Chita Bay and weakened that the water flows out of the bay. Consequently, the high water level condition in the bay persisted during the surge in Mikawa Bay.

愛知県三河湾における海岸植物の種多様性に影響する要因

愛知県三河湾における海岸植物の種多様性に影響する要因

Erratum: Adverse effects of dead zones in the coastal waters on the bay-wide material cycle and its remedial measures ―An analyze with the ecosystem model in Mikawa Bay, Japan― [Journal of Advanced Marine Science and Technology Society Vol. 19 No.2 (2014) p. 27

Erratum: Adverse effects of dead zones in the coastal waters on the bay-wide material cycle and its remedial measures ―An analyze with the ecosystem model in Mikawa Bay, Japan― [Journal of Advanced Marine Science and Technology Society Vol. 19 No.2 (2014) p. 27

Distribution of Virulence Markers among Vibrio vulnificus Isolates of Clinical and Environmental Origin and Regional Characteristics in Japan

Background Vibrio vulnificus is an opportunistic human pathogen that is widely distributed in estuarine environments and is capable of causing necrotizing fasciitis and sepsis. In Japan, based on epidemiological research, the incidences of V. vulnificus were concentrated in Kyusyu, mainly in coastal areas of the Ariake Sea. To examine the virulence potential, various genotyping methods have recently been developed. This study aimed to investigate the distribution of virulence markers among V. vulnificus isolates of clinical and environmental origin in three coastal areas with different infection incidences and to determine whether these isolates have the siderophore encoding gene viuB.Methodology/Principal FindingsWe examined the distribution of genotypes of the 16S ribosomal ribonucleic acid (rRNA) gene, vvhA, vcg, and capsular polysaccharide (CPS), and the presence of viuB in 156 isolates collected from patients and environmental samples in Japan. The environmental samples were collected from three coastal areas: the Ariake Sea, Ise & Mikawa Bay, and Karatsu Bay. The results showed disparity in the ratios of genotypes depending on the sample origins. V. vulnificus isolates obtained from patients were classified into the clinical type for all genotypes. In the environmental isolates, the ratios of the clinical type for genotypes of the 16S rRNA gene, vvhA, and vcg were in the order of the Ariake Sea>Ise & Mikawa Bay>Karatsu Bay. Meanwhile, CPS analysis showed no significant difference. Most isolates possessed viuB.ConclusionsMany V. vulnificus belonging to the clinical type existed in the Ariake Sea. Three coastal areas with different infection incidences showed distinct ratios of genotypes. This may indicate that the distribution of clinical isolates correlates with the incidence of V. vulnificus infection.

三河湾に発生する‘想定外’高潮とその発生機構

三河湾に発生する‘想定外’高潮とその発生機構

三河湾における高潮の特性に関する一考察

Three events of storm surge which yielded different tidal departures in the head of Mikawa Bay are compared and discussed from the viewpoint of response to the wind forcing. The mechanism of sudden sea level rise is investigated based on the data of wind, sea level and velocity obtained in the period of three different Typhoons which passed near the bay. The magnitude of preceding east wind which gives rise to the sea level in Ise Bay and quick change in wind direction from east to west are key factors to the development of large tidal departure in the head of Mikawa Bay. The propagation of surge waves as a free long wave is confirmed through the velocity profile data and also tested using a 2D simple numerical model.

温暖化シナリオA1Bの下での最大級台風による三河湾の高潮とその特性解明

温暖化シナリオA1Bの下での最大級台風による三河湾の高潮とその特性解明

三河湾における貧酸素水塊の消長過程に関する数値的研究

The long-term variations of density structure and hypoxia were examined numerically with a quasi three-dimensional numerical ocean model in order to elucidate the dynamic process of hypoxia in Mikawa Bay. The numerical results revealed that the bottom water was isolated by density stratification due to the increase in temperature and river inflow in summer season and the dissolved oxygen in the isolated bottom water was consumed, resulting in the formation of hypoxia. Moreover, the MODIS SST and the observation data were assimilated into the numerical simulation by the nudging method to furthermore improve the computation accuracy. The validity of data assimilation in Ise Bay area was confirmed from the comparison of the numerical results and the observation data.

Quantification of a Macrobenthic Community's Response to Hypoxia Around a Borrow Pit in the Inner Part of Mikawa Bay, Japan

Quantification of a Macrobenthic Community's Response to Hypoxia Around a Borrow Pit in the Inner Part of Mikawa Bay, Japan

三河湾奥での貧酸素水塊の発達特性と港湾域の影響について

三河湾奥での貧酸素水塊の発達特性と港湾域の影響について

Development of an Air–Water Temperature Relationship Model to Predict Climate-Induced Future Water Temperature in Estuaries

To predict climate-induced change in aquatic environments, it is necessary to understand the thermal constraints of various fish species and to understand the timing of current and projected coastal temperatures. This paper presents a newly developed model of the relationship between air and water temperature that was constructed on the basis of harmonic analysis. The model is novel because it requires only a single variable (air temperature) to predict water temperature and captures the hysteresis patterns of the rising and falling limbs and their historic memories. The model was calibrated and validated with data collected from monitoring buoys in Mikawa Bay, Japan between 2005 and 2009. The model validation showed a good performance with a root mean squared error (RMSE) in the range of 0.8–1.0°C. It is especially encouraging that the suggested model can predict water temperature with a reasonable level of accuracy once an acceptable relationship between air temperature and water temperature has been constructed from previously measured data.

The Nautical Chart, “Ise Sea and Mikawa Bay” in 1893

The Nautical Chart, “Ise Sea and Mikawa Bay” in 1893

Distribution of ephyrae and polyps of jellyfish Aurelia aurita (Linnaeus 1758) sensu lato in Mikawa Bay, Japan

We surveyed the distribution of colonies of polyps of Aurelia aurita sensu lato (s.l.) in Mikawa Bay, Japan. First, we surveyed the distribution of ephyrae of A. aurita s.l. at 75 stations encompassing the whole of Mikawa Bay in early 2008. A total of 37 ephyrae were sampled mostly from fishing ports. Ephyrae were most abundant around the islands located near the mouth of the bay, and decreased from the western part to the eastern part of Mikawa Bay. Next, we selected five fishing ports in Mikawa Bay where ephyrae occurred and surveyed the underside of floating piers and underwater overhangs of wharfs. We found dense colonies of polyps of A. aurita s.l. under nearly all of the floating piers at the two islands located near the mouth of the bay. Fitting a logistic regression model to the dataset showed that the percentage coverage of Aurelia polyps was significantly greater at the two islands compared with the other locations. In addition, the coverage of Aurelia polyps was greater when the coverage of other fouling organisms was in the range of 65–90%, and the coverage of Aurelia polyps was lower on floating piers with a vinyl surface and on concrete wharfs. The combined distribution of polyp colonies of A. aurita s.l. in Ise Bay and Mikawa Bay suggested that A. aurita s.l. in the two bays probably forms a single population and shoals of medusae mainly originate from protected harbors along the mouth-part of the bays.

Specific accumulation mechanism of marine particles in a borrow pit in Mikawa Bay

Specific accumulation mechanism of marine particles in a borrow pit in Mikawa Bay

Behavior on Production Form of Clam Ruditapes Philippinarum Fishing with Active Clam Fry-released Methods in the Three Bays (Tokyo bay, Mikawa bay and Hiroshima bay) in Reduction Period of Clam Fry Supply from Other Prefectures

Behavior on Production Form of Clam <i>Ruditapes Philippinarum</i> Fishing with Active Clam Fry-released Methods in the Three Bays (Tokyo bay, Mikawa bay and Hiroshima bay) in Reduction Period of Clam Fry Supply from Other Prefectures

Influence of Hypoxic Water on Early Growth of the Ark Shell Scapharca kagoshimensis in Mikawa Bay, Japan

Influence of Hypoxic Water on Early Growth of the Ark Shell Scapharca kagoshimensis in Mikawa Bay, Japan

Structures of Water Mass and Current in Shallow Waters off River Mouth Located in a Bay

Intensive field measurements of water quality and current were carried out in summer 2010 off the Toyogawa river mouth located at the head of Mikawa Bay. Structures of water density and dissolved oxygen concentration and their variations were discussed based on the data. The residual currents were compared with wind data and freshwater discharge from the river. The estuarine circulation observed in the measurement seemed to be caused mainly by wind action, but large amount of freshwater discharge may cause current toward the river mouth near the bottom. Dissolved nutrients especially phosphorus may be transported upstream by the bottom flow and used in the primary production in shallow waters.

A model for measuring leaf growth rate of vegetative shoot in the seagrass, Zostera marina

A new model for determining leaf growth in vegetative shoots of the seagrass Zostera marina (eelgrass) is described. This model requires the weights of individual mature and immature whole leaves and leaf plastochrone interval ( P L) as parameters, differing from the conventional leaf marking technique (CLM) that requires cutting and separation between new and old tissue of leaves. The techniques required for the model are the same as for the plastochrone method, but the parameters differ between both methods in use of the weight of individual immature leaves. In a mesocosm study, eelgrass growth was examined, and parameters for the new model and plastochrone method (the weights of individual mature and immature leaves and P L) were measured. Leaf growth rate was measured using the CLM and determined by the new method and the plastochrone method. The results were then compared between the CLM, the new model, and the plastochrone method. The results obtained with the new model were similar to those obtained with the CLM. However, the results of the plastochrone method differed from those of the CLM, while the weight of immature leaves varied seasonally. The new model was also used to determine leaf growth in a natural eelgrass bed in Mikawa Bay, Japan, and revealed the growth rates in all shoots and those of different ages. This method would be advantageous as an accurate means of direct measurement in fieldwork, and should therefore be a useful tool for monitoring seagrass growth.

Carbon and nitrogen stable isotope analysis on the diet of Jomon populations from two coastal regions of Japan

We report on a stable isotope paleodietary reconstruction of Jomon populations in Japan during the Middle to Final Jomon period (ca. 5000–2300 years BP), focusing on dietary differences within and among populations and between regions. Carbon and nitrogen isotope analysis was performed on human and faunal bone collagen from six coastal sites along the Inland Sea in the Sanyo (Ota, Funamoto, and Tsukumo) region and along Mikawa Bay and the Pacific Ocean in the Tokai (Kawaji, Yoshigo, and Inariyama) region. We found that carbon and nitrogen isotope ratios were positively correlated, indicating that the Jomon people consumed a mixed diet of marine (shellfish and marine fish) and terrestrial (C 3 plants and terrestrial mammals) protein. In the Ota samples (n = 25, during the Middle Jomon period, 5000–4000 years BP), sex was one of the main reasons for the intra-population dietary variation. Ota males consumed greater amounts of marine food, while Ota females consumed greater amounts of terrestrial food; these dissimilar diets may have been related to the sexual division of labor. Significant inter-population dietary differences were found, which may have been related to differences in age or site location. Notably, the two coastal regions showed clear isotopic differences. Nitrogen isotope ratios of individuals from the Sanyo region were significantly higher than ratios of individuals from the Tokai region. The individuals in the Sanyo region might have consumed a diet high in aquatic foods, particularly high trophic level marine fish, whereas the individuals in the Tokai region might have consumed a lot of marine shellfish. Another possible reason for the regional isotopic difference might have been different baseline of nitrogen isotope ratios of the marine ecosystems.