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Population outbreaks of the coral-eating starfish, Acanthaster planci, are hypothesized to spread to many localities in the Indo-Pacific Ocean through dispersal of planktonic larvae. To elucidate the gene flow of A. planci across the Indo-Pacific in relation to ocean currents and to test the larval dispersal hypothesis, the genetic structure among 23 samples over the Indo-Pacific was analysed using seven highly polymorphic microsatellite loci. The F-statistics and genetic admixture analysis detected genetically distinct groups in accordance with ocean current systems, that is, the Southeast African group (Kenya and Mayotte), the Northwestern Pacific group (the Philippines and Japan), Palau, the North Central Pacific group (Majuro and Pohnpei), the Great Barrier Reef, Fiji, and French Polynesia, with a large genetic break between the Indian and Pacific Oceans. A pattern of significant isolation by distance was observed among all samples (P = 0.001, r = 0.88, n = 253, Mantel test), indicating restricted gene flow among the samples in accordance with geographical distances. The data also indicated strong gene flow within the Southeast African, Northwestern Pacific, and Great Barrier Reef groups. These results suggest that the western boundary currents have strong influence on gene flow of this species and may trigger secondary outbreaks.

A numerical wave-absorption filter has been developed for an open boundary condition in the analysis of nonlinear and irregular wave evolution. The filter is composed of a simulated sponge layer and Sommerfeld's radiation condition at the outer edge of the layer. The wave-absorption characteristics of the filter have been investigated by applying the linear potential theory and a two-dimensional nonlinear boundary element model. In both cases, the filter is found to he applicable for a wide range of wave parameters. In order to realize an idealized “numerical wave tank”, the present model also incorporates a nonreflective wave generator in the computational domain composed of a series of vertically aligned point sources. Numerous numerical experiments demonstrate that the present approach is effective in generating an arbitrary wave profile without reflection not only at the open boundaries but also at the wave generator.

A new simple model to evaluate quasi-3-D suspended sediment transport in a non-equilibrium state has been developed through a formulation based on a kind of weighted residual concept. The model includes only two unknown variables to be solved in a horizontal 2-D domain ( x , y ); i.e., the sediment concentration at the bottom C b ( x , y , t ) and the shape factor A ( x , y , t ) in the assumed exponential curve for the vertical profile of the concentration, both of which are the most important factors governing the nonequilibrium sedimentary process. From the computational results for the 1-D deposition and erosion problems, the model has been confirmed to give satisfactory results in accuracy and in computational time. The present model has also been applied to the 3-D suspended sediment transport problem in the nearshore region including the surf zone. The comparison between the computational results by the present model and those by the conventional models assuming the local equilibrium concentration profile and the nonequilibrium but vertically uniform profile, have demonstrated the importance of taking the effect of the nonequilibrium 3-D condition into the consideration for such problems.

自由表面近傍に大きな渦度を伴った波・渦共存場の基本的な力学過程の解析を目的として, 境界要素法と離散渦法に基づいた解析法を新たに開発した. 次に, 自由表面近傍に単一渦や渦対が存在する基本的なヶースの解析例を示し, それらの特性を明らかにした. 最後に, 砕波帯内の波動場を念頭において, 正弦波の前面から一定の割合で渦素子を供給した場合の計算結果を示し, 砕波帯内では波の非線形性や分散性の効果に加えて渦度流速成分の存在が波形変形に有意な大きさの影響を及ぼし得ることを明らかにした.

It was shown through a questionnaire survey that sounds of breaking waves on a beach axe one of indispensable natural factors to constitute beach amenity. Analyses of sounds recorded on several bea...

Sound of breaking waves on beaches is one of the important factors affecting amenity of beach environment. To incorporate the auditory factor int θ the design process for beach, physical characteri...

As one of powerful tools for the design in coastal space, where waves and their sounds have significant roles as factors constituting amenity of the space, a dynamic simulator of landscape and auditory environments has been developed, being based on Computer-Graphics techniques and incorporating a sound processing system, To realize the simulator system on a work-station (20MIPS, 32Mb), several inventions to reduce computational time and storage domain are introduced in the software system both in themethod of the CG expression and of the calculation of waves. The validity and availability of the present system have been confirmed through an application to a specific plan of construction of artificial beaches.

Recently the Tokyo urbanized area becomes more vulnerable to thunderstorm-like heavy rain rather than the rain acompanied with typhoon (Tamashima et al.1990). Hence in the present study an attempt has been made to analyze the characteristics of the generation and evolutional process of cloud cells in the Tokyo metropolitan area by using of a 3D radar system. The results of the analyses for typical three cases of 31 July 1987, 13 August 1988, and 17 August 1988 suggest that in addition to the heat island effect due to the urbanized area, the existence of Tokyo Bay as a cool island and a source of water vapor also affects the evolutional process of cloud cells.

Microalgal-based indicators were used to assess terrestrial influence on Shiraho coral reef of Ishigaki Island (Okinawa, Japan). A typhoon occurred on 4–5 August 2005 and sampling were made on three occasions thereafter (6, 8, and 11 August). Pre-typhoon sampling was conducted on 26 July. The typhoon-enhanced terrestrial discharges increased reef nutrient levels (e.g. average NO 3 - -N: 0.088 mg/L pre-typhoon to 0.817 mg/L post-typhoon). This elevated chlorophyll-a concentrations by four times and shifted phytoplankton composition (spectral class-based) from an initial dominance of diatoms and green microalgae to the dominance of bluegreen microalgae (cyanobacteria) and cryptophytes. Cyanobacteria later increased by more than 200% and accounted for as much as 80% of total chl-a (∼0.29 μg/L), possibly assisted by favorable nutrient availability. In outer reef waters, diatoms and green microalgae predominated whereas cyanobacteria and cryptophytes were nearly undetectable. Due to detrital decomposition and river discharge, the CDOM was much higher in the inner reef than in the outer reef. Benthic bluegreen microalgae were relatively more abundant in areas close to the river mouth and coastal agricultural fields. At these locations, nutrient concentrations were much higher due to river discharge and potentially significant groundwater discharge. Thus, phytoplankton and benthic microalgae can serve as indicators of terrestrial influence on coral reefs.

[1] We measured the gas-transfer velocity (k) and analyzed factors regulating k at coral reefs and an estuary at Ishigaki Island, Japan, using the floating-chamber method and the measured energy-dissipation rate (ɛ) to represent turbulence in a small-eddy model. We confirmed the validity of the floating-chamber method quantitatively for the first time by the comparing ɛ values inside and outside the chamber device. We also compared k to ɛ and empirical parameters such as wind and current speeds. Measured k had a low correlation with the empirical parameters and a high correlation with ɛ, as indicated by the small-eddy model. The high ɛ values may have been regulated by topographic conditions, e.g., corals or seagrasses that generate wakes, and complex coastlines or large-scale (on the order of kilometers) topographic factors that generate horizontal current shear. Our measurements indicate that coastal k is regulated by ɛ and cannot be accurately determined using wind or current speeds. Topographic conditions in coastal regions are important factors that regulate ɛ; thus, a quantitative analysis of the effects of these conditions is necessary to accurately determine coastal air–water gas flux.

Background The crown-of-thorns starfish, Acanthaster planci (L.), has been blamed for coral mortality in a large number of coral reef systems situated in the Indo-Pacific region. Because of its high fecundity and the long duration of the pelagic larval stage, the mechanism of outbreaks may be related to its meta-population dynamics, which should be examined by larval sampling and population genetic analysis. However, A. planci larvae have undistinguished morphological features compared with other asteroid larvae, hence it has been difficult to discriminate A. planci larvae in plankton samples without species-specific markers. Also, no tools are available to reveal the dispersal pathway of A. planci larvae. Therefore the development of highly polymorphic genetic markers has the potential to overcome these difficulties. To obtain genomic information for these purposes, the complete nucleotide sequences of the mitochondrial genome of A. planci and its putative sibling species, A. brevispinus were determined and their characteristics discussed. Results The complete mtDNA of A. planci and A. brevispinus are 16,234 bp and 16,254 bp in size, respectively. These values fall within the length variation range reported for other metazoan mitochondrial genomes. They contain 13 proteins, 2 rRNA, and 22 tRNA genes and the putative control region in the same order as the asteroid, Asterina pectinifera. The A + T contents of A. planci and A. brevispinus on their L strands that encode the majority of protein-coding genes are 56.3% and 56.4% respectively and are lower than that of A. pectinifera (61.2%). The percent similarity of nucleotide sequences between A. planci and A. brevispinus is found to be highest in the CO2 and CO3 regions (both 90.6%) and lowest in ND2 gene (84.2%) among the 13 protein-coding genes. In the deduced putative amino acid sequences, CO1 is highly conserved (99.2%), and ATP8 apparently evolves faster any of the other protein-coding gene (85.2%). Conclusion The gene arrangement, base composition, codon usage and tRNA structure of A. planci are similar to those of A. brevispinus. However, there are significant variations between A. planci and A. brevispinus. Complete mtDNA sequences are useful for the study of phylogeny, larval detection and population genetics.

To efficiently perform the numerical simulation in a R-type mangal, in which the horizontal scales of the creek and the swamp are quite different, we attempt to apply a nesting procedure to the highly resolved current simulation in the mangrove area at Fukido River of the Ishigaki Island, Okinawa, Japan. In the computation, we introduce three computational domains with the different grid resolutions. The results indicate that the numerical performance of the nesting procedure used here is confirmed for the tidal current simulation in the mangrove estuary through the comparison of the observed and computed results. It should be also found that the present numerical model can simulate complicated flow structures around the creeks.

One of the key concerns in coral reef monitoring by remote sensing is to determine the effects of various optically-active constituents (i.e. suspended sediments, chlorophyll-a and yellow substances) present in the coastal waters to the observed reflectance produced by remote sensors. Quantification of these constituents is important since they serve as primary indicators of coral health and their probable waterborne environmental stressors. This paper describes the coupling of coral canopy bidirectional reflectance models previously developed by the authors with a two-flow radiative transfer solution specific to coastal waters to study the sensitivity of spectral reflectance of coral reef areas with combinations solid suspended matter and chlorophyll-a concentrations at various viewing and illumination conditions. Spectral field measurements including surface and subsurface reflectance profiles of coral-bottomed waters were obtained. Chlorophyll-a concentration and turbidity data were gathered from the field by deployment of field instruments. Results indicate comparable reflectance profiles produced by the computational model relative to field data, especially at shallower depths with weaker influence of chlorophyll-a concentration, more so at high concentration of suspended sediments. Inversion methods applied to coral reef reflectance modeling is likewise discussed, particularly its performance in the estimation of coral morphological parameters given variations in suspended sediment concentration and chlorophyll-a values.

A method based on a four flux model has been developed to accurately estimate multiple-substance concentrations in seawater for the case the backscattered light from the sea bottom is not ignored because of the shallow depth. Three selected substances were assumed to be in the sample area, and the concentration of each substance was estimated from an aerial MSS image. The results estimated were compared with sea data, and the concentrations were estimated much better than that of our previous model in which the sea bottom was ignored.

This paper presents a simple and highly accurate stability estimation method for armor units covering breakwater rubble mounds against tsunami overflow. In this method, overflow depth is used to represent the external force. This enables an easier and more robust estimation of the required mass of the armor units than the conventional method based on flow velocity. This method takes into account the influence of the impingement position of the overflow jet and the influence of harbor-side water depth, both of which are important factors for armor stability. Numerical computation is also carried out aiming at the establishment of a stability analysis method for armor units. The validity of the computation method is confirmed by comparing the measured current field. The stability of armor units is investigated by computing the hydraulic force acting on each armor unit.

A method based on a four flux model has been developed for a more accurate estimation of multiple-substance concentrations in the water. The results estimated by real Landsat TM for the northern part of Tokyo Bay were in good agreements with the sea truth data, assuming that chlorophyll-(alpha) , suspended mineral, and dissolved organic matter exist in the area.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

With the focus on the characteristics of temporal and spatial fluctuations of the bottom-sediment properties and their vertical distributions around the mouth of the Tama River in Tokyo Bay, the properties of surface sediments, such as grain-size distributions and water contents, had been monitored by taking bottom-sediment core samples from several sampling stations around the river mouth with the intervals of 3 month for a period of five years from 2006 through 2010. Based on the monitored data, the impact of flood events which occurred during the survey period on bottom sediment properties and the recovery processes after the flood event were evaluated. This study clarified that seasonal fluctuations of surface bottom sediment qualities clearly appear on river mouth shoals and tidal wetlands and the impact of the river flood was relatively slight and the damages were restored over relatively short period of time after the flood event. On the other hand, the flood event remarkably caused rapid decline of the water content of bottom sediments at offshore of the river mouth, and it took about three years for their bottom sediments to return to its normal as before the flood event. This paper also discusses the recovery process of the sediment properties at the offshore region and shows that the long-term evolution of the sediment properties was caused by the constant settling of new deposition of suspended particles from the water column and accumulation rate was estimated at 2.5 cm per year.

Dadhich, A.P., and Nadaoka, K., 2012. Analysis of terrestrial discharge from agricultural watersheds and its impact on nearshore and offshore reefs in Fiji. The coral reef ecosystems are rapidly deteriorating due to intense anthropogenic perturbations in the river basins in northwest Viti Levu Island, Fiji. This study aimed to assess the change in benthic cover as influenced by terrestrial loadings from the 14 adjoining agriculturally dominated (especially sugarcane) coastal watersheds using remote sensing, a geographic information system (GIS), and a physically based, distributed hydrological model. An integrated modeling framework with land-use change was constructed to simulate the runoff, sediment yield, and nutrient discharge using the Soil and Water Assessment Tool (SWAT) model. The impact of terrestrial discharge on the coastal ecosystem was investigated by spatio-temporal analysis (1992–2007) of the benthic cover using Landsat TM/ETM+ data. Due to the cropland expansion, a significant amo...

Temporal variability of carbon and nitrogen stable isotope ratios (δ13C and δ15N) in bivalves were investigated from May 2007 to February 2009 at two different stations in Tamagawa River estuary, Japan, together with chemical and isotopic compositions of potential food sources, such as suspended particulate matter and surface sediment. δ13C and δ15N in bivalves were enriched in the downstream station irrespective of the species. δ13C and δ15N of bivalves in both stations showed seasonal cycle, in which they were enriched in summer and depleted in winter. At both stations, remarkable decrease of clam δ13C was observed after a high flood discharge, indicating strong influence of terrestrial organic matter inflow. In conclusion, it is revealed that δ13C and δ15N in bivalves are useful markers to trace time-integrated information of estuarine environments.

Modeling of key processes for fine sediment transport dynamics near the sea bed with fluid mud layer has been studied for the inner Tokyo Bay considering the mud characteristics of the site. Field monitoring data have revealed some specific features of the muddy sediment around the study site such as high water content at the bottom surface and fluid mud transport. Resuspension flux is estimated as turbulent diffusion flux between the sea water and fluid mud layer and estimation results show fairly good agreement with observed data. For the estimation of horizontal mass flux in the fluid mud layer, velocity profiles are analytically calculated using the relationship between shear stress and deformation rate for Bingham fluids considering the vertical structure or yield stress profile in the observed fluid mud layer.

We monitored temporal variations of a bottom sediment quality and benthic species diversity based on sediment sampling and analysis around the Tama river mouth in the Tokyo Bay. The monitoring started in 2006 and we focused on the impact of the extensive flood event in September 2007 on the benthic environment. As a result, the diversity and biomass of the benthic species were increased after the flood especially in the off shore of the river mouth. The re-colonization of the benthic biota is considered to be related with the favorable change in the sedimentary environment for the species with disappearance of fluff layer on the bottom surface by the flood event.