Ariake Bay Research Articles

Sensitivity of Salt-leached Clay Sediments in the Ariake Bay Area, Japan

This study aims to determine whether the principle that “divalent cation predominance in the pore water precludes quick clay development” applies to the Ariake Bay sediments. The chemical and geotechnical properties of an Ariake clay sediment are presented, and sensitivity is discussed with a focus on pore-water salinity and cation composition. In recent years, reduction of pore-water salinity has occurred due to permeation of river water through the sediments because of overpumping of groundwater. Sodium remains the dominant pore-water cation in an upper zone, whereas divalent cations are dominant in the deeper zone. Divalent cation domination in the deeper zone is ascribed to Ca release from nearby cement-stabilized sediments and to Mg increase in response to a change in river water quality. The upper zone's sensitivity ranged from 15 to 77, and the remolded strength was mostly <0.5 kPa, such that quick clay was present over much of its depth. In contrast, the deeper zone's sensitivity was <40, and its remolded strength exceeded 0.5 kPa; quick clay was not present despite the <2 g/L salinity. The absence of quick clay is ascribed to the high remolded strength caused by the pore-water divalent to monovalent cation ratio being greater than 0.25.

Spatiotemporal occurrence and feeding habits of tonguefish,Cynoglossus lightiNorman, 1925, larvae in Ariake Bay, Japan

Summary Spatiotemporal occurrence and feeding habits of tonguefish (Cynoglossus lighti Norman, 1925) larvae were investigated in an offshore area (>5 m in depth) of the inner part of Ariake Bay, Japan. All specimens were symmetric, free-swimming larvae. Although their seasonal abundance and distribution in the study site varied from year to year, spawning started in June and the larval abundance was high in August and September with a wide distribution in the inner part of the bay. Both present and previous study results strongly suggest that larvae may settle primarily in the estuary and near-shore areas of Ariake Bay after their wide distribution in the offshore area of the bay during the free-swimming stage. Larvae showed a clear feeding rhythm in which they fed on prey mainly during the daytime. Larvae fed exclusively on copepods, and identified prey were mostly Paracalanidae (mainly Parvocalanus crassirostris), Microsetella norvegica, and Oithona davisae. Pre-metamorphosis larvae fed primarily on Paracalanidae and O. davisae, whereas O. davisae formed a smaller proportion of the early-metamorphosis diet. In early metamorphoses, larvae fed preferentially on Paracalanidae and M. norvegica.

Community assembly by limited recruitment in a hypoxia-stressed soft bottom: A case study of macrobenthos in Ariake Bay

Community assembly by limited recruitment in a hypoxia-stressed soft bottom: A case study of macrobenthos in Ariake Bay

Quick Clay Development and Cation Composition of Pore Water in Marine Sediments from the Ariake Bay Area, Japan

By analyzing the cation composition of pore water in the soil samples of Ariake Bay sediments, the present study assesses the development of quick clay by leaching in both the original and seawater-saturated soil samples. Divalent cations were dominant in the pore water of the original soil sample, whereas Na+ was the major cation in that of the seawater-saturated soil sample. The cation proportion in the pore water for both soil samples remained the same after leaching. The difference in pore water cation composition between the original and seawater-saturated soil samples affected how their geotechnical properties changed through leaching. The undisturbed shear strength of both soil samples remained almost the same, but a large disparity between the soil samples was observed in the remolded shear strength: it remained almost the same in the original soil sample after leaching. Hence, sensitivity was not increased and quick clay was not formed. However, in the seawater-saturated soil sample, the remolded shear strength decreased to a great extent, and quick clay with a sensitivity exceeding 700 developed. The lack of development of quick clay in the original soil sample is attributed to the dominance of divalent cations in the pore water, and the development of quick clay in the seawater-saturated soil sample is ascribed to the dominance of Na+ in the pore water.

A New Species of Eagle Ray Aetobatus narutobiei from the Northwest Pacific: An Example of the Critical Role Taxonomy Plays in Fisheries and Ecological Sciences

Recent taxonomic and molecular work on the eagle rays (Family Myliobatidae) revealed a cryptic species in the northwest Pacific. This species is formally described as Aetobatus narutobiei sp. nov. and compared to its congeners. Aetobatus narutobiei is found in eastern Vietnam, Hong Kong, China, Korea and southern Japan. It was previously considered to be conspecific with Aetobatus flagellum, but these species differ in size, structure of the NADH2 and CO1 genes, some morphological and meristic characters and colouration. Aetobatus narutobiei is particularly abundant in Ariake Bay in southern Japan where it is considered a pest species that predates heavily on farmed bivalve stocks and is culled annually as part of a ‘predator control’ program. The discovery of A. narutobiei highlights the paucity of detailed taxonomic research on this group of rays. This discovery impacts on current conservation assessments of A. flagellum and these need to be revised based on the findings of this study.

Evolutionary mechanisms shaping the genetic population structure of coastal fish: insight from populations of Coilia nasus in Northwestern Pacific

A number of evolutionary mechanisms have been suggested for generating significant genetic structuring among marine fish populations in Northwestern Pacific. We used mtDNA control region to assess the factors in shaping the genetic structure of Japanese grenadier anchovy, Coilia nasus, an anadromous and estuarine coastal species, in Northwestern Pacific. Sixty seven individuals from four locations in Northwestern Pacific were sequenced for mitochondrial control region, detecting 61 haplotypes. The length of amplified control region varied from 677 to 754 bp. This length variability was due to the presence of varying numbers of a 38-bp tandemly repeated sequence. Two distinct lineages were detected, which might have diverged during Pleistocene low sea levels. There were strong differences in the geographical distribution of the two lineages. Analyses of molecular variance and the population statistic ΦST revealed significant genetic structure between China and Ariake Bay populations. Based on the frequency distribution of tandem repeat units, significant genetic differentiation was also detected between China and Ariake Bay populations. Isolation by distance seems to be the main factor driving present genetic structuring of C. nasus populations, indicating coastal dispersal pattern in this coastal species. Such an evolutionary process agrees well with some of the biological features characterizing this species

Occurrence and Source of Chlorinated Polycyclic Aromatic Hydrocarbons (Cl-PAHs) in Tidal Flats of the Ariake Bay, Japan

In this study, we hypothesize that natural photochemical reactions of polycyclic aromatic hydrocarbons (PAHs) in tidal flats are responsible for the occurrence of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs). This study aims to survey the impact of photochemical reactions using a combination of field surveys and lab-scale experiments. Concentrations and profiles of PAHs and Cl-PAHs in road dust and sediments collected from seven tunnels and two watersheds, respectively, were determined. In the lab-scale experiments, anthracene was irradiated with ultraviolet (UV) light under various salinity conditions. No detectable Cl-PAHs were found in the road dust. However, Cl-PAHs were detected in the sediments from 700 to 6.1 × 10(3) pg g(-1) and specifically from downstream sites. 2-Monochloroanthracene (2-Cl-ANT) and 9,10-dichloroanthracene (9,10-di-Cl-ANT) were dominant in the sediments. In the Domen River watershed, the ∑Cl-PAHs and the salinity showed a significant positive correlation (p < 0.01) in the sediments, while such a correlation was not found for PAHs. 2-Cl-ANT, 9-monochloroanthracene, and 9,10-di-Cl-ANT were identified as transformation products in the UV irradiation experiments. Production of these Cl-PAHs was dependent on the solution salinity. These results support our hypothesis, and we conclude that photochemical reactions significantly contribute to the occurrence of Cl-PAHs in the studied tidal flats.

Seasonal variations of water column nutrients in the inner area of Ariake Bay, Japan: the role of muddy sediments

To investigate seasonal variations of nutrient distribution in the mudflat-shallow water system, we conducted field surveys once a month from August 2007 to July 2008 in the inner area of Ariake Bay (IAB), Japan. The NH4 (+)-N concentration of the water column increased in autumn because of the high NH4 (+) release from the sediments, ranging from 850 to 3,001μmol m(-2) day(-1). The NO3 (-)-N concentration was maximal in January, which was thought to be caused by NO3 (-) release from the oxic sediments and by NO3 (-) regeneration due to water column nitrification. The PO4 (3-)-P concentration of the water column was high in summer-autumn due to the high PO4 (3-) release from the reduced sediments, ranging from 22 to 164μmol m(-2) day(-1). We estimated the total amounts of DIN and PO4 (3-)-P release (R DIN and [Formula: see text], respectively) from the muddy sediment area of the IAB. In summer-autumn, R DIN and [Formula: see text] corresponded to about 47.7% of DIN input and about 116.6% of PO4 (3-)-P input from the river, respectively. Thus, we concluded that the muddy sediments were an important source of nutrients for the water column of the IAB during summer-autumn. In addition, we found that phosphorus necessary for the growth of Porphyra (Porphyra yezoensis, Rhodophyceae) would be insufficient in the water column when phosphorus during the Porphyra aquaculture period is supplied only from the river. Therefore, the phosphorus release from the muddy sediments was thought to play an important role in the sustainable production of Porphyra in Ariake Bay.

有明海奥部底質における吸着態NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;の季節変化とその影響因子

有明海奥部底質における吸着態NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;の季節変化とその影響因子

Characteristic features of the 1792 Shimabara Landslide Tsunami deposits in Ariake Bay

Characteristic features of the 1792 Shimabara Landslide Tsunami deposits in Ariake Bay

有明産タイラギの生物モデルによる大量へい死原因仮説

有明産タイラギの生物モデルによる大量へい死原因仮説

Estimation of Groundwater-Derived Nutrient Inputs into the West Coast of Ariake Bay

Estimation of Groundwater-Derived Nutrient Inputs into the West Coast of Ariake Bay

II-4. 有明海のクルマエビ放流におけるDNA 解析

II-4. 有明海のクルマエビ放流におけるDNA 解析

諫早湾奥からの物質輸送過程と有明海異変に関する考察

The largest change in the Ariake Sea before and after coffering by a closing levee in the Isahaya Bay are appearances of a regulating reservoir and intermittent discharge of deteriorated fresh water from it to the Isahaya Bay. People are prone to think that the water discharge from the reservoir flow straight out through the central and the mouth parts of the Ariake Bay and that its impact on the inner part of the Ariake Sea is slight. To make sure of this, we carried out numerical advection -diffusion simulations of conservative substance supplied steadily from the inner part of the Isahaya Bay and made it clear that it stayed in the inner part of the Ariake Sea at high concentration in a steady state. This fact is quite reasonable from the point of view of hydraulics and fluid dynamics. Therefore there is a strong possibility that the deterioration of water quality in the regulating reservoir extends widely over even the inner part of the Ariake Sea.

有明海北東部海域における溶存態ケイ素と珪藻類の変遷

沿岸生態系への溶存態ケイ素(DSi)の影響を把握するために有明海北東部海域のDSiを含む栄養塩濃度とプランクトンを調査した. 同海域では年二回のDSi濃度の減少がみられた. 特に毎年2-3月の濃度減少が大きく, 溶存無機態リン(DIP)濃度も枯渇する状況にあった.この減少は大型珪藻Eucampia spp.等の増殖によるものと考えられた. その際の栄養塩比DSi/DINについては1以下, DSi/DIPについては10以下と著しく低下していた. このような栄養塩比に空間的分布が生じていたが, 地点間の珪藻プランクトンの発生状況に大きな違いは見られなかった. 毎年2-3月の栄養塩濃度低下時には, DSi濃度は珪藻の増殖制限濃度に近つき, その後2ケ月程度は珪藻の繁殖が抑制されていた.

有明海北岸低地で新たに発見された中部更新統の年代と堆積環境

有明海北岸低地で新たに発見された中部更新統の年代と堆積環境

Effect of Embanking on the Sea water Exchange Rate and the Current Velocity into Ariake Bay’s Sea Algae Field

Effect of Embanking on the Sea water Exchange Rate and the Current Velocity into Ariake Bay’s Sea Algae Field

Discovery of an early Middle Pleistocene marker tephra around the Ariake Bay area, Southwest Japan

中部更新世前期のテフラが筑紫平野とその周辺の堆積物コアと露頭から発見された．鉱物の種類組成，屈折率，化学組成，フィッショントラック年代に基づき，このテフラは約0.6 Maに東九州から噴出した由布川火砕流堆積物（Yfg-pfd）に対比される．

Trends in Population Density and Shell Length of the Planktonic Larva Ruditapes philippinarum in Ariake Bay

Trends in Population Density and Shell Length of the Planktonic Larva Ruditapes philippinarum in Ariake Bay

Influence of Resuspended Sediments and Their Surface Accumulation on a Pen Shell Atrina pectinata in Ariake Bay, West Japan

Influence of Resuspended Sediments and Their Surface Accumulation on a Pen Shell Atrina pectinata in Ariake Bay, West Japan