Environmental dynamism in the complex ecosystem of coral reef, seagrass bed and mangrove forest

点击翻译按钮获取中文摘要

In order to evaluate the environmental dynamism in the complex ecosystem of coral reef, seagrass bed and mangrove forest, we conducted three types of research. One is the transect measurement of nutrient flux as well as physical movement of water between coral reef-seagrass bed-mangrove forest ecosystems.Second is the GIS of underwater environment, i.e. seagrass bed and coral reef. Using a remotely operated vehicle (ROV) equipped with a submersible digital camera and a quadrat, we obtained still and video images of these ecosystems. The data were arrange according to the ship records. User can select any records from PC display, and can see the underwater scenery along the ship recordThird is to investigate how these ecosystems depend on one another from the viewpoint of organic geochemistry. We analyzed chief primary producers and sediment in each ecosystem for the distribution of lipid biomarkers and the ^<13>C content of total organic carbon. Lipids in the terrestrial higher plants … More were characterized by the distribution of n-alkanes high at C29/C31, high content of diterpenes (e.g., phyllocladene), high content of triterpenones (e.g., friedelin), and the predominance of triterpenols (e.g., b-amyrin) over sterols. Lipids in the seagrasses were characterized by the distribution of n-alkanes high at C21, C23, and C25, lowcontent of triterpenones, and the predominance of sterols (e.g., b-sitosterol) over triterpenols. Lipids in corals were characterized by the presence of sterols (e.g., gorgosterol) and the absence of n-alkanes, triterpenones, and triterpenols. Lipids in the sediments from mangrove forest were found to resemble those in the terrestrial higher plants. Lipids in the sediments from seagrass bed were characterized by high content of triterpenones, and the predominance of triterpenols over sterols, reflecting a major input of organic matter from mangrove forest. Lipids in the sediment from coral reef did not include triterpenones nor triterpenols.The data of ^<13>C content of TOC also suggested that the contribution of terrestrial organic matter was large to the sediments from seagrass bed, but little to the sediment from coral reef. We therefore conclude that seagrass bed works as a barrier against terrestrial input, and protects coral reef from eutrophication in the subtropical ecosystems in Ishigaki Island. Less