三方湖では,アオコの種組成としてMicrocystis属とPlanktothrix属が交代に優占していることが確認されている。この2種類は,これまで塩分に対して各々の増殖特性を持っていることが知られている。そこで,この論文では,三方湖で見られる2種類の藍藻の遷移過程を数値モデルで表現することを試みる。塩分に対する耐性に関する培養実験では,M.aeruginosaは塩分が5以上では増殖されないことを確認した。この現象は、現地の調査でも塩分が5以上となる三方湖の北部入り口で同種が観測されなかったことと一致した。しかし,P.agardhiiは三方湖の全域で観測された。培養結果に基づき塩分と水温による内的自然増殖率(μ)と環境収容力(Κ)および種間競合係数(γ_<i,i>)を定式化した。そして,Boxモデルで再現した数値計算結果と現地観測結果を比較した結果,モデルの妥当性を証明することができた。

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The mega-infaunal community of an artificial tidal flat in Mikawa Bay was investigated for two years in order to evaluate its biological production and water purification function. A total of 47 species were identified, which was comparable to natural tidal flat in Mikawa Bay. The dominant species were the bivalves, such as Mactra chinensis, Ruditapes philippinarum and the crustaceans, Portunus trituberculatus. During the first six months of the research period, the abundant biomass of bivalves at the artificial tidal flat resulted in higher removal rate of particulate organic nitrogen, which fell within the range of a natural tidal flat in Mikawa Bay. However, the biomass of bivalves drastically decreased in accordance with the appearance of diving ducks and mass fishery. This study suggests that the biomass of mega-infaunal community in artificial tidal flats may drastically decrease by predation or fishery if the areas of created tidal flats are small.

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日本海のソデイカ立縄漁具は,箱形のブイ,幹縄(loom),錘,および枝糸(8mおよび15m長)を介した2個の擬似餌で構成されている。本研究では,小型水深計を錘部と擬似餌部の計3箇所に装着し,水深や三者の位置関係から挙動を計測した。投入された漁具は,錘,擬似餌部の順で沈降し,最大水深に達するまでの平均沈降速度は40〜51cm/secであった。錘部と擬似餌部は,3.5〜4分間で最深帯に到達した後,安定状態に到った。漁具位置関係(相対角度)は,漁具の沈降中だけでなく,安定状態時でも絶えず変化していた。漁獲水深帯は,海流が弱い条件下では幹縄の全長よりもわずかに小さい程度であったが,海流が強い時には幹縄の全長よりも20〜30m浅く,想定した水深帯で漁獲されていない可能性が示唆された。

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Concerning the appropriate plan and site for the creation of fishing ground. function of water purification. network between tideland and zostera bed and present ecological value of site should be considered based on material cycle. The achievement of sustainability and effective productivity of the created fishing ground and the balance of ecosystem around the created fishing ground are realized through the imitating natural ecosystem analyzed by material cycle. The accuracy of ecological index. theoretical intelligibility. calculating profit, convenient measuring and effective management method are needed for management of bivalve fishing ground by fisher and fisheries cooperative association. There are obtained studying material cycle.

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The sudden decrease of catch of corbicula calm in Lake Hinuma was caused by overfishing of corbicula, progress of desalination and formation of anoxic waters. In order to achieve both restoration of corbicula fishery and water quality conservation, the environmental assessment in brackish lake was carried out by ecosystem model that assess the function of purification and biological production. The effect and influence on the water route making in Hinuma River as case study was examined. By the water route making in Hinuma River, the seawater exchange was promoted and the salinity in Lake Hinuma was risen. On the other side, the reduction of dissolved oxygen and the rise of nutritive salts density was caused in the upper Lake Hinuma. The rise of dissolved oxygen and the reduction of nutritive salts density was caused from the lower Lake Hinuma to Hinuma River. The rise of corbicula resource was caused in Lake Hinuma. The reduction of corbicula resource was caused in Hinuma River.

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Lake Ogawara, located in Northern Japan, is a brackish lake with the surface-area of 63km^2. The maximum depth is about 25m, and approximately 12psu of salt water exists in a lower layer under the depth of 20m throughout the year. Lots of Corbicula Japonica are living in the lake, and about 2500 tons are taken out as fishery product. We develop an ecological model to consider the biochemical processes of the bivalve, that calculates water temperature, salinity, chlorophyll-a, inorganic nitrogen and phosphorous, organic nitrogen and phosphorous, COD and dissolved oxygen. We make one-dimensional calculations to clarify the seasonal variabilities in water qualities and nutrients cycle, and use a three-dimensional hydrodynamic model coupled with the ecological model to clarify the spatial distributions of water qualities. It is found that an increase of nutrient supply from the lower layer, caused by the intense vertical mixing, makes phytoplankton blooming active, and that the spatial distribution of the phytoplankton greatly depends on the habitat distribution of Corbicula Japonica. The calculation results for the nutrients cycle show that the amount of phosphorous consumed at primary production is more dependent on the biochemical and physical processes occurred in the lake than the inflow load supply. About 20% of primary production is ingested by Corbicula Japonica, and its purifying function is about 30% for COD. Because Corbicula Japonica stores nitrogen internally, the concentration of total nitrogen in the lake water is restrained and decreases in October in spite of the time of the maximum primary production.

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In order to discuss the optimum future management plan for sustainable fishery, the numerical ecosystem model has been applied to Lake Saroma, which is one of the major sources of farmed scallops in Japan. The model includes the pelagic ecosystem, the benthic ecosystem and the scallop growth model. These factors were dynamically linked each other in the model. This structure provided the model with an ability to predict future water quality and production of scallops with sediment changes. As the preliminary step of discussion about the future management plan, the material flows during/after the spring bloom period in the lake were evaluated using the model. Then, the influences of the scallop aquaculture on the material cycle were evaluated quantitatively by comparing the cases-with and without the scallop aquaculture. The results show the followings. 1) The spring bloom had a great influence on scallop juvenile's growth, and the subsequent lower trophic level period didn't have a bad influence on the growth due to the rational farming cycle. 2) Since the farmed scallops kept 30% of N in the pelagic system in their body and were finally harvested, the aquaculture generally purified the water quality in the lake. However, the aquaculture would generate worse water quality at the bottom in the summer. Because the aquaculture has also the function like a pump that transfers the particle organic matter from the water to the sediment, the increased organic matter in the sediment would cause more release of nutrients and consumption of DO in the summer.

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It is known that the short-necked clam play an important role on the matter cycle in the tidal flats in Mikawa Bay. Therefore, even when modeling suspension feeder that the short-necked clam represented was described in detail based on the indoor experiment results and applied to some tidal flats, excellent reproducibility was obtained. However, we could not obtain the good reproducibility about the Mesocosm data set reproduced by an existing model and the parameter set applied to the tidal flats. Therefore, it verifies and accuracy of an existing tidal flat ecosystem model has improved by using the continuous data set obtained with Mesocosm, and the in existence data set of Isshiki tidal flat in Mikawa Bay calculated in the past was calculated again, and both were compared. In the results of the calculation by the modified model, a higher primary production and a faster matter cycle in the tidal flats are expressible compared with a past model, and, the characteristic of the dynamic matter cycle in the tidal flats is being reproduced. It is become clear that the ecosystem model and the parameter to who improved it by using the data of Mesocosm being able to reproduce the biomass of a different annual in a real sea area, and being able to do the nitrogen circulation analysis.

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The purpose of pearl farming is the pearl production that is a jewel. The healthy growth of pearl shell is important for production of high quality pearls. Therefore the environmental evaluation of pearl farming fishing ground was carried out as follows. Firstly the environmental items of pearl farming fishing ground such as water temperature, salinity, tidal flow, nutritive salts, feeds density, growth & survival rate of pearl shell and so on were examined. Next the relation between growth of pearl shell and quality of cultured pearl were examined. Thirdly the quality assessment of cultured pearl which used HEP (Habitat Evaluation Procedure) method was suggested. Fourthly the ecosystem model that considered pearl farming was applied to Asou bay in Tsushima Island, and was verified its appropriateness on the basis of pearl faming examination.

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