Part Of Ariake Bay Research Articles

Weekly Observations of Estuarine Microbial Assemblages during Summer in the Inner Part of Ariake Bay, Japan; Microbial Water-sediment Coupling in Turbid Shallow Waters.

Estuarine microbial assemblages are altered by a number of environmental factors, and knowledge of these changes is essential for understanding the functions of microbes in estuarine ecosystems. The aims of the present study were to examine the relationship between microbial assemblages in the water column and sediment surface, and to identify the environmental factors that influence the short-term dynamics of microbial assemblages in these two zones in summer in the inner part of Ariake Bay. The microbial assemblage of each sample consisted of a mean of 71.1% operational taxonomic units (OTUs), which commonly occurred in the water column and sediment surface, although their relative composition markedly differed between the two zones. In the water column, spatiotemporal changes in microbial assemblages correlated with several environmental factors, such as the nitrogen content in suspended particles, turbidity, and salinity. On the other hand, temporal changes in the sediment’s microbial assemblages were governed by a single environmental factor, namely, the oxygen reduction potential. These results suggest that the composition of microbial assemblages in the water column and sediment surface differed even in highly turbid brackish waters with high sediment resuspension, and the environmental factors contributing to the change in the assemblage composition also differed between the water column and sediment.

Population dynamics of a hypoxia-tolerant bivalve: A comparison of two sites in the inner part of Ariake Bay, Japan

Population dynamics of a hypoxia-tolerant bivalve: A comparison of two sites in the inner part of Ariake Bay, Japan

A relationship between the mechanisms of the environmental crisis in the inner part of Ariake Bay and the reclamation project of the tidal flats conducted in Isahaya Bay

A relationship between the mechanisms of the environmental crisis in the inner part of Ariake Bay and the reclamation project of the tidal flats conducted in Isahaya Bay

Contribution of the development of the stratification of water to the expansion of dead zone: A sedimentological approach

To test a hypothesis that the development of the stratification of water enhances the phytoplankton blooming and hypoxia without any increase in the nutrient loading in an enclosed bay, the present study examines the spatial relationship among the hydrographic structures, physico-chemical conditions of the sediments, and macrobenthic communities at 21 stations in the inner part of Ariake Bay, Kyushu, Japan in August 2010, and compares the distribution of the mud content of the sediment in 2014 with those of last few decades focusing on the succession of sedimentary environment. The stratification of water developed in the innermost part of Ariake Bay, and hypoxia occurred below the well-stratified water. The distribution of the muddy bottom with high content of organic matter derived from phytoplankton almost overlapped with the stratified water. Cluster analysis concerning the grain size composition of the sediment corresponded greatly to that of the macrobenthic communities. These results indicate that the development of the stratification of water strongly influences the sedimentary environments and the community structure of macrobenthic animals in the inner part of Ariake Bay. Comparison with the past distribution of mud content revealed eastward expansion of the muddy sediment, and it suggests the distribution of the well-stratified water has expanded recently. The results of the present study show the possibility that the development of the stratified water causes a series of phenomena, which closely resemble ones following the development of the eutrophication of the water, without any increase in the nutrient loading in an enclosed bay or estuary.

Life history of Sternaspis costata (Sternaspidae: Polychaeta) in Ariake Bay, Japan

The life history of the Japanese sternaspid polychaeteSternaspis costatavon Marenzeller, 1879 was investigated in the inner part of Ariake Bay from May 2010 to May 2011, with additional sampling in July and September 2011. All the worms were measured by the width of the ventral shield (WS) as an indicator of body size, and their coelomic contents were also examined. Ovigerous females occurred throughout the year, except during October and March, with the highest ovigerous rate (number of ovigerous females/number of adults with a WS larger than that of the smallest ovigerous female, i.e. 1.8 mm) noted in September (43.8% in 2010, 34.7% in 2011). The ovigerous rate was less than 10% in the other months, except in April 2011 (30%). Although the coelomic oocytes ranged from 90 to 160 μm in diameter, the diameters of most of the oocytes were 140–160 μm in September. The number of adults drastically decreased from September to October, suggesting that most of the adults died after spawning in the major reproductive period, although a small fraction of adults seemed to reproduce earlier or later. A cohort of recruits with an approximately 1.2 mm WS was identified in March and April. Most of the recruits grew to adult size in July–September, when many ovigerous females occurred. These results indicated that this species is fundamentally semelparous, with longevity around 1 year, and they mostly reproduce in September, with a few adults reproducing almost throughout the year.

Implications of changes in the benthic environment and decline of macro-benthic communities in the inner part of Ariake Bay in relation to seasonal hypoxia

Implications of changes in the benthic environment and decline of macro-benthic communities in the inner part of Ariake Bay in relation to seasonal hypoxia

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.

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.

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

Effects of hypoxia and organic enrichment on estuarine macrofauna in the inner part of Ariake Bay

In the inner part of Ariake Bay, Japan, hypoxia frequently occurs in summer at the organically enriched bottom with salinity stratification caused by flooding after the rainy season. Sediment organic enrichment can work as a stressor for macrobenthos. To investigate the effects of both hypoxia and sediment organic enrichment on macrobenthos, samples were collected at 20 stations by grab sampling in May and August, representing the situation before and after hypoxia, respectively. Although sediment grain size did not change, sediment TOC increased significantly in August. Multivariate analyses showed that the community structure changed significantly in August. The variation in the community structure among stations also increased, which indicated disturbance by stressors during the study period. Similarly, the species richness and total abundance of macrobenthos decreased significantly after hypoxia even after the TOC effect was removed. In addition, the amount of TOC change and the abundance of the main species did not correlate in any case. These results suggest that the community changes during the study period are not caused by stress from the increased sediment TOC but are mainly from the subsequent hypoxic stress.

Primary Production and Decomposition Dynamics of Particulate Organic Matter in the Inner Part of Ariake Bay

In order to obtain the background information about characteristics of particulate organic matter (POM) in the inner part of Ariake Bay, oxygen consumption rate of bottom water including POM and primary production rate were investigated. Additionally, relationships between biochemical composition of POM and oxygen consumption capacity, controlling factor of primary production were examined. In summary, it was suggested that contribution of oxygen consumption by POM, especially originated from the marine phytoplankton, plays an important role for the formation of hypoxia in the inner part of Ariake Bay. Primary production rate were varied widely among observation dates and it was suggested that nitrogen is limiting nutrient in this are during summer.

有明海湾奥部干潟域のマクロベントス相

有明海湾奥部干潟域のマクロベントス相

Citrate-dithionite-bicarbonate extractable phosphorus (CDB-P) pool in the suspended and surface sediments of the tidal flat area in inner Ariake Bay, Japan

CDB-P (phosphorus extractable by the citrate-dithionite-bicarbonate extraction procedure) was used as the indicator of bio-available inorganic P in the suspended and surface sediments in the inner part of Ariake Bay. The CDB-P pool of suspended and surface sediments in the tidal flat area was estimated to be 10 ton and 90 ton, respectively (total of 100 ton), which corresponds to 1.5 times the average dissolved inorganic phosphorus standing stock. During the summer periods of hypoxia, the CDB-P concentration in the surface sediments decreased with the decline of Eh, losing 43–47% of the CDB-P observed in April. These results suggest that the phosphorus dynamics have been affected by the decrease of resuspended sediment concentrations brought about by the reduction of the tidal currents and phosphate release from the surface sediments during frequently occurring summer hypoxia events.

Benthic fauna of the inner part of Ariake Bay: long-term changes in several ecological parameters

We investigated the benthic fauna of the inner part of Ariake Bay in August 2006. We set 45 sampling stations including at 28 mud and 17 sand bottoms in subtidal areas. In each station, sediment samples were taken once with a Smith-McIntyre grab. The sediment samples were sieved with a 1 mm mesh, and the residue was fixed with 10% formalin solution. In the laboratory, benthic organisms were sorted, identified and weighed by their wet weight. The data obtained were compared to the samples collected in 1989. In both mud and sand bottoms, benthic fauna in 2006 was dominated by bivalves and polychaetes as in 1989. However, the abundance of polychaetes, bivalves, ophiuroidea, and the other taxa except crustaceans significantly or nearly significantly decreased from that in 1989 irrespective of bottom types, leading to an overall decrease in macrobenthos. The biomass of mud bottoms tended to decrease from that in 1989, though did not differ in the sand bottom. The distribution of bivalves dominating in 1989 also drastically decreased. The cause of the drastic decrease in macrobenthos may represent the consequence of the frequent occurrence of hypoxia in summer and/or change in sediment grain size, both of which have recently occurred in the inner part of Ariake Bay.

Tidal asymmetry of the sediment transport in estuaries and its amplification by the weir.

Vertical profiles of the velocity, turbidity and salinity were observed over one tidal cycle in the Hattae estuary in the inner part of Ariake Bay which contains wide tidal flat. The vertical pro-files are more uniform in the flood stage than those in the ebb stage. This tidal asymmetry causes net upstream transport of the suspended sediment. Closing the gate of the weir weakens the ebb currents but not the early flood current, thus will intensify the tidal asymmetry further.