CONSERVATION OF TROPICAL SEAGRASS BEDS WITH SPECIAL REFERENCE TO THEIR ROLE ON FUNCTION OF COASTAL ECOSYSTEM

在“热带海草床的保护及其对沿海生态系统功能的作用”的标题下进行了实地研究，以量化陆地营养物质、沉积物物质和海岸线的人类变化对海草生态系统的压力，包括面向泰国安达曼海一侧的底栖生物种群。以下是本项目的主要研究成果。1)分析了优势种海草对外界环境变化（如泥沙供给、光照强度降低）的适应情况。指出了海草形态适应的重要性，包括垂直根状茎的细根，以及光合产物在上下底间分布的调整。2)海草各部位氮、碳、硫稳定同位素比值可作为小尺度环境胁迫的良好指标。3)从大河口位置到无河流流入影响的不同环境背景下，海草物种多样性和生物量分布的比较表明，至少在本研究区，随着河流影响的增加，海草生物量和物种多样性都呈下降趋势。4)通过海草沉积物再悬浮的物理强迫观测，确定了海草沉积物再悬浮的3个因素，即潮流、风致再悬浮和入流或陆源固体。即使在较窄的海草床范围内，这三个因素的时空变化也会影响与海草床相关的底栖生物的代谢。5)研究了儒艮对不同类型海草的食物偏好，以及嗜盐菌床对该地区儒艮饮食的重要性。

Field studies were conducted under the title "Conservation of tropical seagrass beds with special reference to their role on function of coastal ecosystem" to quantify the stress of terrestrial nutrients, sediment materials and human changes of coastal line on seagrass ecosystem including benthic populations facing to the Andaman Sea side of Thailand. Followings are major research outcomes of this project.1) We analyzed how the dominated species of seagrass adapts to external environmental change such as sediment supply and decrease of light intensity. And we indicated the importance of morphological adaptation of seagrasses including the fine roots of vertical rhizomes, as well as adjustment of photosynthetic products distribution among upper and below bottom.2) Stable isotope ratios of nitrogen, carbon and sulfur within the various parts of seagrasses could be used as a good indicator of small scale environmental stress. on seagrass metabolisms3) Comparison of species diversity and biomass distributing different environmental setting, from the location of big river mouth to that of no river inflow influence, indicated that both biomass and species diversity of seagrass decreased with the increase of river influences at least in this study area.4) Based on the field observations of physical forcing causing re-suspension of seagrass sediments, we identified three factors, i.e., tidal current, wind induced re-suspension and inflow or terrestrial solids. Even within the rather narrow area of seagrass beds, spatial and temporal variation of these three factors were observed, also effecting on metabolisms of benthic organisms associated with seagrass beds,5) Food preference of dugong for different types of seagrass species was examined and importance of Halophila beds for the diet of dugong of this area.