Ariake Bay Research Articles

On the season for starting culture of Wakame, Undaria pinnatifida in the Ariake Bay

On the season for starting culture of Wakame, Undaria pinnatifida in the Ariake Bay

Late-stage metamorphosing Conger myriaster leptocephali collected in a river estuary of Ariake Bay, Japan

Little is known about where anguilliform fishes complete metamorphosis from the leptocephalus to juvenile stage. Conger myriaster leptocephali in the final stages of metamorphosing were collected from the estuarine portions of the lower Rokkaku River and in the northwest region of Ariake Bay. Three metamorphosing leptocephali with PAM/TM ratios of 0.27–0.34 were collected in the lower river, and five (PAM/TM, 0.30–0.46) were collected at sea stations in the bay. The collection of metamorphosing larvae of this species in a river estuary with lower salinity and high turbidity raises the question of how much these habitats are used by the metamorphosing larvae of this marine eel species.

Growth, survival and feeding of ark shell Scapharca kagoshimensis with hung and settled culture in Ariake Bay, Japan

Growth, survival and feeding of ark shell Scapharca kagoshimensis with hung and settled culture in Ariake Bay, Japan

Age, Growth and Hatching Dates Based on Otolith Increments of Larvae and Juveniles of the Roughskin Sculpin Trachidermus fasciatus (Scorpaeniformes : Cottidae) in Ariake Bay, Kyushu Island, Japan

Age, Growth and Hatching Dates Based on Otolith Increments of Larvae and Juveniles of the Roughskin Sculpin Trachidermus fasciatus (Scorpaeniformes : Cottidae) in Ariake Bay, Kyushu Island, Japan

The Relationship between Sexual Maturation and Glycogen Contents in Visceral Organs of the Pen Shell Atrina pectinata in Ariake Bay, Japan

The Relationship between Sexual Maturation and Glycogen Contents in Visceral Organs of the Pen Shell Atrina pectinata in Ariake Bay, Japan

Occurrence of “Suminori” Disease in Nori Culture Farms at Saga Prefecture Facing the Inland of Ariake Bay

Occurrence of “Suminori” Disease in Nori Culture Farms at Saga Prefecture Facing the Inland of Ariake Bay

Assessment of carbon- and fluorescence-based primary productivity in Ariake Bay, southwestern Japan

A comparative account of primary productivity (PP), in the characteristically turbid and highly dynamic waters of Ariake Bay, measured by 13C uptake and fast repetition rate fluorometer (FRRF) was conducted to ensure compatibility between the two methods. Estimates from both methods depicted strong linearity for both short-term (r 2 > 0.90) and daily (r 2 = 0.42–0.93) measurements, except in the near-surface (∼0 m) layer. 13C-based short-term (1 h; in situ) PP estimates showed similar magnitudes and trend with the instantaneous PP measured by FRRF concurrently. Whereas, unlike short-term measurements, the daily PP estimates from both methods showed large difference, with FRRF-based time integrated daily PP resulting in 1.09–1.82 times higher than the carbon-based daily (24 h; simulated in situ) PP. This difference between daily PP estimates was mainly due to: (1) the temporal variation of water column chlorophyll a (Chl a) because of frequent moving of water mass, and (2) the dissimilarity in ambient light field conditions between the two methods. Results revealed that considering the above two environmental factors invariable over a daylength, fairly close approximation of daily PP, compared to 13C-based daily PP, could be obtained from FRRF. Hence, FRRF-based daily PP can be considered as more realistic in this highly dynamic water body like Ariake Bay where water column parameters are subjected to strong temporal variation. The relationship between Chl a-specific photosynthetic rate ( P B ) and the corresponding photosynthetically active radiation (PAR) in the water column (PAR– P B relationship) was found to be linear for FRRF and curvilinear for 13C-based measurements in the near-surface layer, for the same intensities of incident PAR, and this is thought to be the primary basis for the higher difference in PP estimates at the near-surface layer. Considering the minor variations in FRRF-based time series of PAR– P B relationships, a combined and/or instantaneous PAR– P B relationship in combination with incubation Chl a and light field condition was used to obtain fairly close estimates of daily water column integrated PP from FRRF.

Temporal and Spatial Variation of Dissolved Oxygen in Ariake Bay

To remedy the various environmental degradations, it is necessary for its factor to clear widely in Ariake Bay. The cluster analysis as to the temporal variation pattern of dissolved oxygen and the principal component analysis as to its spatial variation pattern were carried out in order to group the dissolved oxygen at the bottom in summer, 2007 in Ariake Bay. As a result, the dissolved oxygen was grouped to 4 patterns by both analysises. The cluster analysis suggested that the continuance of hypoxic water differed from each groups. The principal component analysis suggested that the development- disappearance process of hypoxic water was captured widely.

Anthropogenic decline of the peculiar fauna of estuarine mudflats in Japan

Mudflats are formed in the upper littoral zones in estuaries, especially in the innermost part of macro-tidal embayments (upper reaches of estuaries), providing a habitat for peculiar fauna and flora. The peculiar fauna and flora of estuarine mudflats appear to have been extirpated in many estuaries in Japan, along with the mudflats that have been damaged or destroyed by thoughtless and drastic coastal reclamation. At present, Ariake Bay, which constitutes the largest area of mudflats remaining in Japan, also has the greatest variety of species. The mudflat-specific species are almost or completely restricted to Ariake Bay, while populations of the same (or closely related) species are distributed along Asian continental coasts, which suggests they are continental relicts. Some of the mudflat-specific species now restricted to Ariake Bay (e.g.,the bivalve, Tegillarca granosa, the polychaete, Hediste japonica, the salt marsh plant, Suaeda japonica) previously enjoyed a wide distribution in Japan. Even within Ariake Bay, huge mudflats in Isahaya Bay were recently lost to a reclamation project there. The high productivity of benthic organisms in mudflats seems to benefit carnivores such as birds and fishes (e.g., Japanese eel). Conservation and restoration of mudflats are needed to conserve endangered species and to maintain traditional human fisheries and culture. From this aspect, restoration of the largest mudflats in Isahaya Bay in Ariake Bay is highly desirable.

Spatio-Temporal Variations of Turbulent Energy Dissipation Rate during Stratification Period in Ariake Bay

In recent years in-situ measurements on microstructures are carried out to investigate turbulence structures in shallow sea areas. However it is difficult to figure out turbulent structures near interfaces, such as sea beds, sea surfaces and pycnocline, because of the measuring principle of a commonly-used shear sensor. In this study, field observations on microstructures were carried out in Ariake Bay by using the microstructure profiler which acquires fine-scale temperature gradients. As a result of these observations, spatio-temporal variations of turbulent energy dissipation rate in the northern area of Ariake Bay were observed and it is clarified that the way to estimate turbulent energy dissipation rate from temperature gradients in shallow sea areas is valid especially under strongly stratified condition.

Field Demonstration of "Recovery of Shoreline" in Kumamoto Port

Recently, the various environmental problems such as red tide, anoxic water and etc. occurred in Ariake Bay. Tidal flats in Ariake Bay were reclaimed from pre-Edo era to the post-WWII food shortage period for the main purpose of increasing farmland. In the process, the revetments were constructed to protect farmland existing around the supratidal zone (shoreline). In this study, the field demonstration of rehabilitation technologies for Ariake Bay recovery of was done in Kumamoto Port. As the result, the number of benthos species increased more than those before the shoreline construction.

Analysis of dominant factors of hypoxia generation mechanism in Ariake Bay, using pelagic - benthic coupled ecosystem model.

Analysis of dominant factors of hypoxia generation mechanism in Ariake Bay, using pelagic - benthic coupled ecosystem model.

Field Observation on Suspended Sediment Transport Process off Tidal Flat in Upper Ariake Bay

A field measurement was carried out to elucidate fine sediment transport processes off the north-western shore of the Ariake Bay, Japan. Time series data analysis of hydrodynamic forcing and suspended sediment properties shows that the increments of suspended sediment concentration during a tidal cycle under spring tide condition are due to multi processes including both local resuspension by strong tidal current and advection effect of turbid water from near shore region. The field data also shows the variability in the suspended sediment properties such as settling velocity and particle size over a tidal cycle indicating relatively higher settling velocity during ebbing tide and finer median grain size during low tide.

Cryptic Species and Historical Biogeography of Eel Gobies (Gobioidei: Odontamblyopus) Along the Northwestern Pacific Coast

Cryptic species are common in gobioid fishes, as revealed by recent molecular studies. This study collected molecular and morphological data to delimit species boundaries and to reveal the historical biogeography of Odontamblyopus lacepedii sensu lato by sampling 87 specimens from 16 locations in the northwestern Pacific. Phylogenetic trees based on mitochondrial NADH dehydrogenase subunit 5 sequences identified three major clades. Clear morphological separations among these clades were detected by examining morphological characters used in taxonomic diagnosis. Therefore, these clades were delineated as three separate species: O. lacepedii sensu stricto (in the East China Sea, Yellow Sea, Gulf of Bohai, and Ariake Bay); O. sp. (in the southern East China Sea and southern Yellow Sea); and O. rebecca (in the Gulf of Tonkin, northern South China Sea, and southern East China Sea). Estimated divergence times were 0.61 +/- 0.15 Ma between O. lacepedii and O. sp., and 2.31+/-0.36 Ma between O. rebecca and O. lacepedii+O. sp. These findings indicate that isolation of marginal seas and habitat fragmentation during major falls in sea level in the late Pliocene and Pleistocene may have been responsible for genetic breaks among Odontamblyopus species in the northwestern Pacific.

Mechanism of the Oxygen-Depleted Water Formation near the Head of the Ariake Bay and its Numerical Modeling

A mechanism of the oxygen-depleted water formation near the head of the Ariake Bay is presented based on the field observation data taken by Seikai National Fisheries Research Institute (2009). The first formation of oxygen-depleted water occurred just after big discharges from rivers due to strong salinity stratification and massive Skeletonema sp. growth. The second formation was occurred in August when thermal stratification was developed and Chattonella sp. grew rapidly by taking nutrients in the bottom with vertically migration. A numerical model to simulate these processes was constructed using DELFT3D. The model reproduced the field data very well and revealed that degradation of detritus derived from phytoplankton in the water column and sediment was the most important for the oxygen consumption process.

A Simple in situ Extraction Method for Dissolved Sulfide in Sandy Mud Sediments Followed by Spectrophotometric Determination and Its Application to the Bottom Sediment at the Northeast of Ariake Bay

We developed a simple in situ extraction method for dissolved sulfide (H2S, HS−, S2−) in sandy mud sediments. All analytical procedures were performed in a sealed system of glass syringes to prevent the volatilization of hydrogen sulfide and the oxidation of sulfide by air. An adequate amount of sandy mud sediment was put in a graduated glass syringe on site immediately after sampling. This procedure was performed using a unique and useful tool ; a plastic syringe had its front portion cut, so as to avoid the attachment of sediment to the inside wall of the syringe. To the sediment sample in the syringe, distilled water, deoxygenated by babbling with nitrogen gas, was injected via a three-way stopcock with another syringe. After mixing well, the sample was filtrated into the other syringe through a filter (0.45 μm). In addition, zinc acetate solution was added to the filtrate in the syringe, and was then spectrophotometrically determined by the methyleneblue method after being brought back to laboratory. The proposed method was successfully applied to bottom sediment samples taken from northeast of Ariake Bay. A high concentration of dissolved sulfide was detected in a warmer season. This method should be useful to evaluate sediment quality and to assess the influence of dissolved sulfide on benthos such as bivalves.

有明海北東部流入河川の溶存態ケイ素濃度の予測

Dissolved silicate (Si(OH)4-Si; DSi) concentration was examined at 38 sampling sites in influent rivers of the northeastern Ariake Bay, and estimated on the basins of a numerical geological map of the sites' watershed. The multiple regression model was used for predicting DSi concentration at the sampling sites using the geological area ratio in their watersheds. The coefficient of determination (R2) obtained was 0.931, indicating that DSi concentration was strongly associated with its geological condition. The geological categories which contribute to DSi concentration in rivers are quaternary volcanic rocks (non-alkali, felsic), volcanic rocks (debris) and quaternary volcanic rocks (non-alkali, pyroclastic flows). This result suggests that the DSi concentration of an arbitrary station in an influent river of the northeastern Ariake Bay can be predicted on the basins of a geological map of the station.

Occurrence and Physiological Condition of the Green Mussel, Perna viridis, in Ariake Bay, Japan

Occurrence and Physiological Condition of the Green Mussel, Perna viridis, in Ariake Bay, Japan

Erratum to: Comparison of the early life histories of two Cynoglossus species in the inner estuary of Ariake Bay, Japan

The larval distribution and feeding habits of Cynoglossus abbreviatus and Cynoglossus lighti were investigated around the Rokkaku estuary in Ariake Bay during October 2004 and March and April 2005. Cynoglossus abbreviatus started and completed metamorphosis at larger sizes than C. lighti. Developmental phases consisted primarily of individuals at metamorphosis and postmetamorphosis, which were mainly distributed inside and just outside the Rokkaku River in March–April for C. abbreviatus and October for C. lighti. Tidal changes in vertical distribution just outside the river mouth differed between the closely related species; C. abbreviatus was distributed in the surface and middle layers at flood tide, and aggregated near the bottom (where the current speed was lowest) at ebb tide. Cynoglossus lighti stayed mainly near the bottom during all tidal phases. Larvae of both Cynoglossus species selectively fed on copepods (Pseudobradya sp.), which were scarce in the waters. These facts suggest that the nursery grounds of the two Cynoglossus species were different in terms of their tidal vertical distribution patterns.

Selective mortality of larval Japanese seabass in Ariake Bay, Japan

This article describes the growth, mortality, and selection patterns in early larval stage of Japanese seabass Lateolabrax japonicus in Ariake Bay, Kyushu, Japan. Japanese seabass larvae were collected from the spawning ground in December 2007, and juveniles were collected from the nursery ground in March 2008. Otoliths were analyzed to produce back-calculated daily records of size-at-age and growth rate. Back-calculated growth rates and sizes were compared between larvae and juveniles to determine whether selective mortality occurred. A weight-specific growth coefficient (G) and instantaneous mortality coefficient (M) were computed, and the recruitment potential was evaluated from the ratio of M:G. Selection for fast-growing and bigger larvae was evident during the 5–14 days after hatching (DAH). Selective mortality acted to preferentially remove fish that were slow growing and/or relatively small members of the cohort at least during the period examined. Trends in the growth rate differences between larvae and juveniles suggested that the selection process continued beyond 14 DAH although the exact duration over which selective mortality occurred was unknown. Survivors of Japanese seabass exhibited traits consistent with all aspects of the ‘growth–mortality’ hypothesis: faster growth, larger size-at-age, and shorter larval stage duration (LSD), i.e., larvae with faster growth, bigger size-at-age and a shorter LSD selectively survived the larval period. Larvae had higher M (0.323) than G (0.159), resulting in the M:G ratio of >1.0 (M:G = 2.031), suggesting that the larval cohort was rapidly losing biomass. Future studies should look to determine the duration over which selective mortality occurs and the timing of transition between M and G (M = G) and accumulation of cohort biomass.