Ariake Bay Research Articles

Histology and Nutritional Condition of the Pen Shells Atrina pectinata Protruded above the Sediment Surface during Summer in the Tidal Flat of Ariake Bay

Histology and Nutritional Condition of the Pen Shells Atrina pectinata Protruded above the Sediment Surface during Summer in the Tidal Flat of Ariake Bay

Occurrence and distribution of settling and newly settled spotted halibut Verasper variegatus and Japanese flounder Paralichthys olivaceus in shallow nursery grounds around Shimabara Peninsula, western Japan

The occurrence and distribution of settling and settled spotted halibut Verasper variegatus were compared with those of Japanese flounder Paralichthys olivaceus in shallow habitats around Shimabara Peninsula, western Japan, to elucidate the settlement and recruitment characteristics of spotted halibut, a rare pleuronectid flatfish in Japan. Push-net sampling conducted at nine sites in March and April 2003 collected spotted halibut from four nurseries located at eastern areas of Shimabara Peninsula in Ariake Bay; Japanese flounder were sampled from eight nurseries. Comparison of microhabitat distributions in a tidal-flat nursery during February–April in 2003–2007 revealed that metamorphosing larvae and juveniles of spotted halibut, which showed the drastic body coloration (black to brown) and behavioral changes (frequent swimming to settlement), were distributed mainly in the lower edge of the intertidal area, whereas Japanese flounder inhabited both intertidal and subtidal areas. Metamorphosing larvae of spotted halibut (12.6–16.5 mm standard length; n = 24) were collected in March when the highest densities were observed, whereas metamorphosing larvae of Japanese flounder (10.0–15.9 mm, n = 55) were observed during March–April. Our results suggest that spotted halibut has a narrower time/space window for recruitment to the specific nurseries compared with Japanese flounder.

Intertidal bare mudflats subsidize subtidal production through outwelling of benthic microalgae

An investigation of food web structures in the northwestern soft-bottom area, including the intertidal and subtidal zones, of inner Ariake Bay, suggests that resuspended BM are substantial for offshore secondary production, and the main source of BM would be outwelling from the intertidal mudflat. Carbon and nitrogen stable isotope ratios were measured for macrobenthos samples from the intertidal mudflats, subtidal fringe and offshore subtidal zones, together with their potential food sources. Carbon and nitrogen signatures indicated that most macrobenthos assimilated offshore particulate organic matters (POM) (δ13C: −23.9 ± 0.1‰; δ15N: 8.2 ± 0.1‰) and benthic microalgae (BM) (δ13C: −16.8 ± 1.5‰; δ15N: 8.0 ± 0.4‰) among other potential sources. The relative BM contribution to filter feeders significantly decreased seaward from about 50% in the mudflats to 25% in the offshore zone, and the 99% confidence intervals of the contribution did not include zero even in the offshore zone.

Morphological variation of pallial organs at sites of differing turbidity: a case study of an arcid bivalve

We investigated morphological differences in specimens of the arcid bivalve Scapharca kagoshimensis collected from two sites differing in turbidity in the inner part of Ariake Bay. First, we confirmed if the specimens collected from the two sites were the same species by comparing the sequences of their nuclear 18S ribosomal DNA (18S rDNA) and cytchrome c oxidase subunit I gene (COI) of mitochondrial DNA (mtDNA), since the closely related species S. inequivalvis could be distributed in one site. The results of DNA analyses showed that specimens from both sites belonged to the same species. Shell morphology, gill and posterior adductor muscle size did not differ between the two populations. However, the size of the labial palp was significantly larger in bivalves living in an area of high turbidity compared with those living in an area with low turbidity. This difference could not simply be attributed to differences in meat content because the total weight of the soft body parts did not differ between the two populations. The labial palp is an organ functioning in preingestive particle selection. Hence, the large palps would presumably be a response to high turbidity conditions in which the need for particle processes increases. To the best of our knowledge, this is the first study demonstrating palp size flexibility in arcid bivalves, and such flexibility could be a factor enabling S. kagoshimensis to successfully exploit a wide area of shallow water in the inner part of Ariake Bay.

Origins of Phosphorus and Nitrogen in Ariake Bay, Japan

Origins of Phosphorus and Nitrogen in Ariake Bay, Japan

Discovery of Halicyclops continentalis (Cyclopidae, Halicyclopinae) from Estuaries and Salt Marshes on the West Coast of South Korea

A cyclopoid species from several salt marshes and estuaries on the west coast of South Korea were identified as Halicyclops continentalis Ueda and Nagai, 2009, recently described from Ariake Bay at northwestern Kyushu, Japan. Detailed examination on the Korean specimens justifies Ueda and Nagai's proposition that the H. sinensis sensu Tai and Chen, 1979 formerly known from the Chinese coast of the Yellow Sea should be identical to H. continentalis. Furthermore, this report reinforces their assumption on the geographical distribution of H. continentalis, that is, the Ariake Bay population is a continental relict of the East Asia continent. Herein, a redescription of the species is provided on the basis of the Korean specimens, with a comment on the morphological comparison among three populations around the Yellow Sea.

諫早湾口北部周辺の流動特性について

Ten years or more have passed since large-scale poor cultured laver harvests which arose in the head of Ariake Bay in 2000 winter.However, except for cultured laver, fish catches including a bivalve has decreased and does not show even a sign of recovery. When the drainage gate is opened over a long period of time, it is thought indispensable towards the Ariake Bay reproduction to investigate the change and influence of the aquatic environment of Isahaya Bay and Ariake Bay before and after opening the drainage gate.In this study, the field observation on flow regime at the northern mouth of Isahaya Bay was carried out under the stratified and mixing condition twice in 2010. As a result, structure of cavity flow appeared at the mouth of Isahaya Bay in all condition of both flood and ebb tide. Now, various flow regime has produced on various conditions at the northern mouth of Isahaya Bay, if potential flow will be recovered by opening the gate, it is expected flow regime changes a lot.

有明海奥部底泥における栄養塩フラックスの季節変化

The seasonal variation of nutrient flux between sediments and water column in the inner area of the Ariake Bay was investigated during May, 2010-November, 2011. The supply amount of organic matter to sea bottom and sediment temperature had important effects on the seasonal variation of NH4+-N concentration in porewater. The seasonal variation of PO43--P concentration in porewater was strongly dependent on those of redox environments in sediments. We found that the sediments were an important supply source of nutrient for the water column in the inner area of the Ariake Bay during summer-autumn. In the Porphyra aquaculture period, the phosphorus release from the sediments was thought to play an important role in the Porphyra production in the Ariake Bay.

Mechanism and Causes of Large-Scale Red Tides in the Inner Part of Ariake Bay

Mechanism and Causes of Large-Scale Red Tides in the Inner Part of Ariake Bay

有明海湾奥西部海域の底質変動特性

有明海湾奥西部海域の夏季における短期的な底質変動を明らかにするために，2011年夏季に水質および底質調査を週1回行った．貧酸素水塊は，淡水流入，低水温・高塩分水の貫入，気象条件によって形成と消滅を繰り返した．硫化水素は貧酸素水塊が形成することによって生成し，台風の影響による時化によって低濃度化した．また，酸化還元電位（Eh）が-180mV程度の領域と高い硫化水素濃度が見られた領域とは対応していた．高い硫化水素濃度が見られた堆積物のpHは7.2程度であったことから7月下旬のサルボウの斃死要因は，貧酸素水塊の形成と硫化水素の生成であることが示唆された．

Proposal of a Method to Improve the Marine Environment of Ariake Bay by Decreasing Its Water Depth

Proposal of a Method to Improve the Marine Environment of Ariake Bay by Decreasing Its Water Depth

有明海北東部タイラギ漁場における海底堆積物中溶存硫化物の経月変化

有明海北東部タイラギ漁場における海底堆積物中溶存硫化物の経月変化

夏季の有明海北西部における海底堆積物の有機物組成の時系列変化と貧酸素水塊の消長

Time series survey of water column and sediments was conducted to clarify the cause of hypoxia at the northwestern part of Ariake Bay in summer. A freshet of the Chikugo River facilitated the stratification in water and phytoplankton bloom, and the phytoplankton was buried deep in the sediment down to ca. 20 cm at the neap tide after a strong mixing by the spring tide and the freshet. The large amount of buried phytoplankton cells rapidly consumed oxygen through the decomposition under the strong stratification which inhibits oxygen supply in water, resulted in the thick reducing condition of the sediment and the hypoxia in bottom water. Strong wind by the typhoon eliminated a hypoxia rapidly. On the other hand, a recovery from the reducing condition of the sediment occurred gradually by the usual tidal mixing.

Modification of the vertically generalized production model for the turbid waters of Ariake Bay, southwestern Japan

The vertically generalized production model (VGPM), which was designed for open ocean waters ( Behrenfeld and Falkowski, 1997a; henceforth BF), was evaluated using in situ measurements of primary productivity (PP) in the characteristically turbid coastal waters of Ariake Bay, southwestern Japan, to develop a regionally modified version of the model. The euphotic depth ( Z eu )-integrated PP (IPP) calculated from the VGPM using in situ chlorophyll a (Chl a) and sea surface temperature (SST) was significantly overestimated (by factors of 2–3), but 52% of the observed variability was explained. The weak correlation could have partially resulted from overestimations by the sub-models embedded in the original VGPM model for estimation of Z eu ( Morel and Berthon, 1989; henceforth MB) and the optimal Chl a-normalized PP ( p opt B ). The sub-model estimates of p opt B and Z eu with in situ p opt B and Z eu showed significant improvement, accounting for 84% of the variability and causing less overestimation. Z eu was the most important parameter influencing the modeled IPP variation in Ariake Bay. Previous research suggested that the Z eu model, which was based on surface Chl a, overestimated in situ Z eu by a factor of 2–3, resulting in weak correlation between the modeled and in situ IPP. The Z eu sub-model was not accurate in the present study area because it was basically developed for clear (case 1) waters. A better estimation of Z eu could be obtained from the in situ remote sensing reflectance ( R rs ) using a quasi-analytical algorithm (QAA) in this turbid water ecosystem. Among the parameters of PP models, p opt B is conventionally considered the most important. However, in this study p opt B was of secondary importance because the contribution of p opt B to the variation in modeled IPP was less than the contribution of Z eu . The modeled and in situ p opt B were weakly correlated with 50% of the data points that overestimated the in situ values. The estimation of Chl a was improved by optimizing the Chl a algorithm with in situ R rs data. Incorporating the QAA-based Z eu and the optimized Chl a and constant (median) p opt B value led to improved performance of the VGPM for the study area. Thus, even though the VGPM is a global open ocean model, when coupled with turbid water algorithms for Z eu and Chl a and constant (median) p opt B , it provided realistic estimates of IPP in the turbid water ecosystem of Ariake Bay.

Isolation and characterization of polymorphic microsatellite markers from Japanese grenadier anchovy (Coilia nasus)

We isolated and characterized 12 novel polymorphic microsatellite loci for the Japanese grenadier anchovy (Coilia nasus) using the method of PCR-based isolation of microsatellite arrays. Sixteen individuals of C. nasus from Ariake Bay in Japan were genotyped using 24 PCR primers to characterize the polymorphism at each locus. The average number of the observed alleles per locus was 11.08 (ranging from 8 to 20). The observed heterozygosity values ranged from 0.562 to 1.0, and the expected heterozygosity values ranged from 0.647 to 0.969. Only one of the twelve loci deviated significantly from Hardy–Weinberg equilibrium, and linkage disequilibrium was not found in any pairs of the loci. These markers can be used to investigate the genetic structure of the C. nasus population.

Clay mineral composition of the core sample from Ariake Bay

Clay mineral composition of the core sample from Ariake Bay

Clay Mineralogical Composition of the Quaternary Sediments Collected in the North Coast of Ariake Bay, and the Relation to Depositional Environment and Weathering in the Terrestrial Condition

Clay Mineralogical Composition of the Quaternary Sediments Collected in the North Coast of Ariake Bay, and the Relation to Depositional Environment and Weathering in the Terrestrial Condition

Differentiation between populations of Japanese grenadier anchovy (Coilia nasus) in Northwestern Pacific based on ISSR markers: Implications for biogeography

Northwestern Pacific provides unique scenarios for studying the roles of geography and ecology in driving population divergence and speciation. To elucidate the phylogeographic pattern of Coilia nasus in Northwestern Pacific, we examined ninety individuals from five localities along the coastal regions of China and the Ariake Bay of Japan by using seven ISSR markers. Analyses of molecular variance (AMOVA) showed that genetic differentiation among groups is relatively high (FCT = 0.1904; P = 0.000). Bayesian analysis of ISSR data also revealed significant population structuring between Chinese and Japanese locations. Phylogenetic reconstructions show reciprocal monophyly in populations between China and the Ariake Bay of Japan. We conclude that the present-day phylogeographic pattern is the result of genetic isolation between Japanese and Chinese populations in the Northwestern Pacific following the glacial retreat, and that life-history traits and ecology may play a pivotal role in shaping the realized geographical distribution pattern of this species.

Possibility of environmental improvement by revival of oyster farming in Ariake Bay

Possibility of environmental improvement by revival of oyster farming in Ariake Bay

Heavy Metal Runoff from a Low Farm Block on the Coastal Creek Area of Ariake Bay in Japan

Heavy Metal Runoff from a Low Farm Block on the Coastal Creek Area of Ariake Bay in Japan