Restoration Technique for Eutrophied Sea Environment by using Circulation Function of Organic Matter in Ecosystem

内海湾和港口的底泥恶化，水质富营养化。在封闭海域普遍采用的垂直筑堤降低了海洋生物生境的复杂性，造成了上层和底层生态系统之间物质循环功能的不平衡。我们的目标是设计一种新型的防波堤，为底栖生物提供空间，并促进水生生态系统中的物质循环。我们还通过生活在海底的普通海参Stichopus japonicus的摄食行为对沉积物进行了改造。1999年12月，在日本德岛市冲绳岛港防波堤前建立了钢铁工厂。我们进行了一些调查，以阐明该植物的特征，包括群落结构和环境条件。在小松岛港和大阪府临库公园泻湖两个地点也进行了使用海参的实地试验。一种普通贻贝（Mytilus galloprovincialis）在工厂和防波堤的垂直壁上都占主导地位。8月份，底部溶解氧浓度在株内降至2 mg/1以下，而株外仍维持在4 mg/1。沉降量在植株外部大于植株内部。相对较低的溶解氧浓度是由于贻贝在植物壁结构上的过量生物量造成的。我们需要改善植物的结构，以便为海参等底栖生物提供栖息地。由于海参的存在，两个试验点的沉积物特征不同。海参存在时AVS含量降低，表明S.japonicus在封闭水体环境下的沉积物再加工中起着重要作用。

Deterioration of bottom sediment and eutrophication of water quality have proceeded in inner bay and harbor. A vertical construction of breakwater which prevails in an enclosed sea area had reduced the complexity of habitats for marine organisms, causing unbalance of material cycle function between pelagic and bottom ecosystems. We aimed to devise a new type of breakwater that would provide a space for benthic organisms and facilitation of material cycle in an aquatic ecosystem. We also focussed on sediment reworking by feeding behavior of a common sea cucumber Stichopus japonicus inhabiting the bottom.A preliminary steel plant was set in the front of the breakwater at the Okinosu harbor located in Tokushima city in December 1999. We conducted several investigations to elucidate the characteristics of the plant including community structures and environmental conditions. Field experiments using sea cucumbers were also carried out at the two sites, Komatsushima port and the lagoon of Rinku Park in Osaka Prefecture.A common mussel Mytilus galloprovincialis dominated at both the plant and the vertical wall of breakwater. Dissolved oxygen concentration at the bottom was decreased below 2 mg/1 inside the plant whereas that outside the plant was remained 4 mg/1 in August. The amount of deposited seston was greater outside the plant than inside it. Relatively low concentrations of dissolved oxygen were resulted from the excessive biomass of mussels on the wall structure of the plant. We need to improve structure of the plant in order to provide habitats for benthic organisms such as sea cucumbers.The characteristics of sediment were different due to the presence of a sea cucumber in both experimental sites. The fact that AVS contents were decreased in the presence of sea cucumbers suggested that S.japonicus had an important role in sediment reworking in a closed aquatic environment.