We examined relationship between vocal behavior of dugongs (Dugong dugon) and (1) time of day and (2) tide around Talibong Island, using passive acoustical observation. Also, we compared the results of several data and investigate whether the same behavior can be observed over different time of year. We used underwater sound data recorded in February and March 2004, November 2006 and January 2008 off southeast of Talibong Island and analyzed the number of calls detected in unit time in relation to time and tide. We also compared the result of the analysis among three months and investigated whether there was any difference. In terms of the effects of time, more calls were detected in nighttime than in daytime (p<0.05). In terms of the effects of tide, there were significant correlation between maximum tidal range and many calls were detected when tidal range was narrow. Our findings suggest that vocalization pattern of the dugongs is influenced by such external factors as time and tidal range.
Recently, Methane Hydrate (MH) in the sea area of Japan has been attracting attention as a future energy resource. In order to promote the development of MH in the future, impact assessment of methane on marine species is necessary to grasp its influence, where methane is one of the decomposition products of MH. This study conducted the ecological effects test to evaluate the acute toxicity of methane on marine organisms, which were 2 species of phytoplankton (Prasinophyte; 1 species, Diatom; 1 species), 5 species of zooplankton (Copepod; 4 species, Decapod; 1 species), and nematode in the eastern Nankai Trough or their allied species. The test conditions were 1 atmoshperic pressure, seawater temperature of 20°C, salinity of 35.0, dissolved oxygen of ≥6.0 mg/L, and within seawater of these conditions, the methane concentration of 17.3 mg/L was set, which is the possible maximum dissolved concentration. Five test concentrations of methane were prepared below 17.3 mg/L at a geometric ratio of 2.1 maximum. For the each test endpoints of phytoplankton, zooplankton, and nematode, inhibition of growth at 72 h, immobility at 48 h, and mortality at 72 h, were set respectively. The result of the tests suggested the acute toxicity of methane on these organisms were not observed. This is because the values of test endpoints remained low level as the methane concentration increased, even at the maximum methane concentration of 17.3 mg/L.
Dead zones are described as areas where few organisms can survive. We estimated the material cycle in dead zones to study the adverse effects of such areas on the bay-wide ecosystem function in Mikawa Bay, Japan. Material cycles were analyzed using the ecosystem model, which incorporates information of macrobenthos biomass variation, reflecting fluctuations in the levels of dissolved oxygen. This study was conducted at an area which was chosen from four types of dead zone, that is, small-scale port, loch, borrow pit, and large-scale port and its associated waterway. The amount of PON (Particulate Organic Nitrogen) outflow from the dead zones in small-scale ports and lochs in Mikawa Bay was estimated to be 25.2 tons between June 6th and September 29th of 2009. This value indicates the amount of PON to be removed across 1.39 km2 of tidal flats in Mikawa Bay. The PON outflow from the small-scale port was estimated to decrease by 23% due to the addition of bivalves in the shallow parts of the small-scale port as a remedial measure. The loch changed from a PON source to a PON sink after an open-cut was made at the head of the loch and the subsequent addition of bivalves in the developed shallow areas as remedial measures. The maximum volume of hypoxic water accumulated in the dead zones at the borrow pits and the large-scale ports and its associated waterway, was estimated to be 6.9 × 107 m3 in total. This value is equivalent to 25% of the volume of coastal waters shallower than 5 m, in Mikawa Bay. The maximum volume of hypoxic water accumulated in the borrow pit decreased by 78% as a result of recontouring of the borrow pit as a remedial measure. The amount of oxygen demand units ODU (Mn2+, Fe2+, H2S, and CH4) upwelling from the bottom of the large-scale port and its associated water way was reduced by 12% by the installation of underwater dikes as a remedial measure. Our results suggest that environmental restoration of dead zones is essential to the recovery of the bay-wide ecosystem function.
The possibility of using the fragment of tile was investigated in the present study, because in the near future of Japan, it may become more difficult to obtain marine sand on a massive scale. This study was conducted at a Tidal Flat Mesocosm System. The effect of the fragment of tile was assessed on the basis of the structure of benthic community, and larval settlement, post-settlement survival of the Japanese littleneck clam (Ruditapes philippinarum). The effects were compared to the dam bank sand (sand accumulated at Yahagi Dam). There was no remarkable difference in the benthic community such as meiobenthos, macrobenthos and the larval settlement, post-settlement survival of Japanese littleneck clam between the fragment of tile and dam bank sand. From these results, the possibility to using the fragment of tile as an alternative material to marine sand was suggested.
The methods of environmental impact assessment are represented in the case of renewable energy in the marine environment. Intended technology covers wind farm, wave, current, and temperature difference. The concept of impact assessment on the fishery environment is recommended as a useful guideline.
We have evaluated major potential for wave energy, ocean thermal energy, ocean current energy, tidal current energy and tidal range energy in Japan. Potential values of these ocean energies were estimated in the form of marine physical energy, installable energy and annual energy production. At first, we have calculated marine physical energy by using only public domain data which were observed or simulated by national agencies. Secondly, we have calculated installable energy and annual energy production by assuming geographical constraint, utilizable energy constraint, power coefficient and capacity factor of power-generating facilities. Total marine physical energy in Japan is estimated to be 1,327 GW. And we have suggested that total annual energy production extracted from ocean energy is from 82 to 260 TWh/year within Japanese sea area where the distance from the shore is less than 30 km.
The activity of Japan on ROE has been evaluated as world top-level at the laboratory level, by the way, Japan is delayed in the actual large proof R&D in the sea area in the other countries more than ten years. Recently, Japan with a few resources has begun to be aimed at the innovation of the ROE development full-scale as the sixth useful area in world, so-called exclusive economic zone (EEZ). This year, the NEDO announced the technical road map toward 2030 of ROE including ocean thermal energy conversion(OTEC) and the wave power generation. Saga University has investigated on REO as only COE on REO in the whole country. Especially, OTEC has been researched as aim at the practical use for about 40 years. OTEC is a system generating electricity with temperature difference between warm sea water of the ocean surface and the cold sea water from depths 600 m to 1,000 m. The 30 kW OTEC device which Saga University has is evaluated on as the device that performance is the highest now in the world. The characteristic of OTEC is stable and multi-purpose, not only the electricity but also seawater water conversion, hydrogen production, lithium collection, the fishing ground reproduction is possible. Saga university has contributed to the development of sustainable energy and water resources that these Japanese technology is asset to the project in U.S.A., France, India, Taiwan now In this session, the current status and future prospect are presented on ROE, mainly on OTEC.
Renewable energy from the ocean is important to solve the global environmental issues as well as to supply for their own country. There are several types of energy resources of the ocean including the tidal energy utilization with long experience. In addition, research of the wave power generation is expected and progressing for large scale. The next stage is to reduce the electrical cost by means of improving energy conversion efficiency, reducing the cost of the device and improving durability of the device intended for more than 100 years.